A chip-type light-emitting semiconductor device includes: a substrate 4; a blue LED 1 mounted on the substrate 4; and a luminescent layer 3 made of a mixture of yellow/yellowish phosphor particles 2 and a base material 13 (translucent resin). The yellow/yellowish phosphor particles 2 is a silicate phosphor which absorbs blue light emitted by the blue LED 1 to emit a fluorescence having a main emission peak in the wavelength range from 550 nm to 600 nm, inclusive, and which contains, as a main component, a compound expressed by the chemical formula: (Sr1-a1-b1-xBaa1Cab1Eux)2SiO4 (0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1). The silicate phosphor particles disperse substantially evenly in the resin easily. As a result, excellent white light is obtained.
|
0. 1. A luminescent layer comprising phosphor particles, ultra-fine particles and a translucent resin,
wherein the phosphor particles are dispersed within the translucent resin and primary particles of the ultra-fine particles have an average particle size in the range from 3 nm to 50 nm, both inclusive.
0. 2. The luminescent layer of
0. 3. The luminescent layer of
0. 4. The luminescent layer of
0. 5. The luminescent layer of
0. 6. The luminescent layer of
0. 7. The luminescent layer of
0. 8. The luminescent layer of
9. A light-emitting semiconductor device utilizing the, comprising:
a luminescent layer of
phosphor particles;
ultra-fine particles including primary particles, the primary particles having an average particle size of equal to or greater than 3 nm and equal or less than 50 nm; and
a translucent resin;
a light-emitting device in combination,; and
a supporter, wherein:
the phosphor particles are dispersed in the translucent resin,
the light-emitting device is disposed on the supporter,
the light-emitting device has a bottom surface facing the supporter, and a main light-extracting surface from which a light is extracted and opposite to the bottom surface,
the luminescent layer is in contact with the light-emitting device only at the main light-extracting surface,
the luminescent layer covers an entirety of the main light-extracting surface, and extends beyond outer edges of the light-emitting device, and
the light-emitting semiconductor device emits mixed light mixed with from light emitted from the light-emitting device and a fluorescence emitted from the phosphor particles.
10. The light-emitting semiconductor device of
0. 11. The light-emitting semiconductor device of
0. 12. The light-emitting semiconductor device of
13. The light-emitting semiconductor device of
14. The light-emitting semiconductor device of claim 13 9, wherein a portion of an upper surface of a portion of the luminescent layer is flat and substantially parallel to the main light extracting surface, and when viewed in plan, the portion of the upper surface is located on a light-extracting surface of inside the outer edges of the light-emitting device is flat and substantially parallel to the light-extracting surface.
15. The luminescent layer of
0. 16. The luminescent layer of
0. 17. The luminescent layer of
0. 18. The luminescent layer of
0. 19. The luminescent layer of
20. The luminescent layer of
the ultra-fine particles include at least one of silicone silicon dioxide and aluminum oxide,
the translucent resin is a silicon silicone resin, and
the luminescent layer has a substantial thickness in the range from equal to or greater than 50 μm to and equal to or less than 1000 μm both inclusive.
21. The luminescent layer of
0. 22. The luminescent layer of
0. 23. The light-emitting semiconductor device of claim 9, wherein a thickness of the luminescent layer is equal to or greater than 100 μm and equal to or less than 700 μm.
0. 24. The light-emitting semiconductor device of claim 9, wherein, when viewed in plan, a part of the supporter is exposed from the luminescent layer.
0. 25. The light-emitting semiconductor device of claim 24, wherein the supporter covers a side surface of the luminescent layer.
0. 26. The light-emitting semiconductor device of claim 9, wherein a space is formed between the supporter, the light-emitting device and the luminescent layer.
|
This application
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1).
Considering the fact that the blue-light-emitting device can achieve a light-emitting semiconductor device emitting excellent white light, the blue-light-emitting device preferably emits light having a main emission peak in the wavelength range greater than 430 nm and less than or equal to 500 nm, more preferably in the wavelength range from 440 nm to 490 nm, both inclusive, and still more preferably in the wavelength range from 450 nm to 480 nm, both inclusive. The yellow/yellowish phosphor preferably emits a fluorescence having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, more preferably in the wavelength range from 560 nm to 590 nm, both inclusive, and still more preferably in the wavelength range from 565 nm to 585 nm, both inclusive.
In terms of crystal stability to heat in the phosphor, heat resistance in light-emitting characteristics, luminous intensity of yellow/yellowish emission and color of light, the values a1, b1 and x in the chemical formula are preferably in the ranges 0<a1≤0.2, 0<b1≤0.7 and 0.05<x<0.1, respectively, more preferably in the ranges 0<a1≤0.15, 0<b1≤0.6 and 0.01<x<0.05, respectively, and most preferably in the ranges 0.01≤a1≤0.1, 0.001≤b1≤0.05 and 0.01<x≤0.02, respectively.
Now, a relationship among the composition range, the crystal structure and the color of emitted light of the silicate phosphor, the characteristics of the silicate phosphor emitting yellow/yellowish light, for example, are described in further detail. As a first case, if both of the values a1 and b1 in the chemical formula of the silicate phosphor are close to zero, the silicate phosphor is likely to have a monoclinic structure or a crystal structure in which an orthorhombic system and a monoclinic system are mixed. As a second case, if the value a1 deviates to larger values from the most preferable range and the value b1 is close to zero, the crystal field around Eu2+ ions is weak. As a third case, if the value a1 is close to zero and the value b1 deviates to larger values from the most preferable range, the silicate phosphor is likely to have a monoclinic structure. As a fourth case, if both of the values a1 and b1 deviate to larger values from the respective most preferable ranges and the value 1-a1-b1-x is close to zero, the silicate phosphor is likely to have a hexagonal structure. In any of the first through fourth cases, the silicate phosphor might be a greener phosphor and emit light with low color purity for yellow. If the value x deviates to smaller values from the most preferable range, the concentration of Eu2+ luminescent centers is low, resulting in low luminous intensity of the silicate phosphor. If the value x deviates to larger values from the most preferable range, the luminous intensity is low because of concentration quenching (of luminescence) or self-absorption caused by Eu2+ ions and, moreover, thermal quenching that the luminous intensity decreases as the ambient temperature of the silicate phosphor increases might occur.
Comparison in excitation spectrum between the silicate phosphor and the YAG-based phosphor shown in
The blue-light-emitting device is a device selected from the group consisting of a blue-light-emitting diode, a laser diode, a surface emitting laser diode, a resonant cavity light emitting diode, an inorganic electroluminescence device and an organic electroluminescence device. In terms of increasing the output power and the lifetime of the light-emitting semiconductor device, diodes such as a light-emitting diode, a laser diode, a surface emitting laser diode and a resonant cavity light emitting diode are superior to other devices.
The Ca mole fraction b1 of the yellow/yellowish phosphor is preferably a mole fraction b2 in the range 0≤b2≤0.6.
In terms of crystal stability to heat in the phosphor, heat resistance in light-emitting characteristics, luminous intensity of yellow/yellowish emission and color of light, the mole fraction b2 is preferably in the range 0<b2≤0.4, more preferably in the range 0<b2≤0.3, and most preferably in the range 0.001≤b2≤0.05.
The orthorhombic silicate phosphor within any of the composition ranges emits yellow/yellowish light highly efficiently with high color purity for yellow when excited the blue excitation light. As a result, light emitted by the light-emitting semiconductor device not only has a high luminous flux but also is white or whitish light with a high color purity for white.
In the light-emitting semiconductor device, the blue-light-emitting device may be a blue-light-emitting inorganic device made of a semiconductor selected from the group consisting of a gallium nitride-based compound semiconductor, a zinc selenide semiconductor and a zinc oxide semiconductor. Such a blue-light-emitting inorganic device, especially a blue-light-emitting device including a light-emitting layer made of a gallium nitride-based compound semiconductor, exhibits a high luminous efficacy. Accordingly, if such a blue-light-emitting inorganic device, especially a blue-light-emitting device including a light-emitting layer made of a gallium nitride-based compound semiconductor, is combined with the silicate phosphor, a light-emitting semiconductor device emitting light with a high luminous flux is obtained.
In the light-emitting semiconductor device, the color of light emitted by the light-emitting semiconductor device may have an emission chromatically point (x, y) in the ranges 0.21≤x≤0.48 and 0.19≤y≤0.45, respectively, in a CIE chromaticity diagram.
This chromatically range includes a large part of the white range. Accordingly, if the color of light emitted by the light-emitting semiconductor device is set within the chromatically range, a highly-demanded white-light-emitting semiconductor device is obtained.
A red/reddish phosphor having an emission peak in the red/reddish wavelength range greater than 600 nm and less than or equal to 660 nm may be provided.
Then, the red/reddish phosphor compensates for a red spectrum which cannot be compensated by the yellow/yellowish phosphor alone, so that the light emitted by the light-emitting semiconductor device includes a wide range of the red spectrum.
Further, a green/greenish phosphor having a main emission peak in the green/greenish wavelength range greater than or equal to 500 nm and less than 550 nm may be provided.
Then, the green/greenish phosphor compensates for a green spectrum which has a high luminous efficacy and which cannot be compensated by the yellow/yellowish phosphor alone, so that the light emitted by the light-emitting semiconductor device includes a wide range of the green spectrum. Accordingly, the light emitted by the light-emitting semiconductor device is white light with a high luminous efficacy with respect to white. The red/reddish phosphor and the green/greenish phosphor may be combined with the yellow/yellowish phosphor.
The green/greenish phosphor is preferably a silicate phosphor containing, as a main component, a compound expressed by the chemical formula:
(Sr1-a3-b3-xBaa3Cab3Eux)2SiO4
(where 0≤a3≤1, 0≤b3≤1 and 0<x<1).
Then, the composition and crystal structure of the green/greenish phosphor are made similar to those of the silicate phosphor emitting yellow/yellowish light. Accordingly, the color unevenness in the light-emitting semiconductor device including the green/greenish phosphor becomes relatively small, and in addition, a new technique is no more required in a process for fabricating the light-emitting semiconductor device, resulting in a simple fabrication process.
The luminescent layer may include a plurality of such silicate phosphor made of compounds mutually differing in composition and each emitting yellow/yellowish light having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive. Then, it is possible to control the color of white light obtained by adding the colors of blue light emitted by the blue-light-emitting device and of yellow/yellowish light emitted by the silicate phosphors.
The luminescent layer preferably includes a translucent resin as a base material; and the yellow/yellowish phosphor is preferably present in the form of dispersed particles in the base material.
Since such a luminescent layer includes substantially neither light absorption factor nor light scattering factor, the luminescent layer exhibits improved light transmissivity. Accordingly, the blue light from the blue-light-emitting device either passes through the luminescent layer without being absorbed and attenuated or contributes to excitation of the phosphor. In addition, since the luminescent layer is in the state that a larger part of the surfaces of the phosphor particles can be irradiated with the blue light, the cross-sectional area of the phosphor particles to be excited increases substantially, so that the phosphor particles in the luminescent layer emit light effectively.
Moreover, since the phosphor in which the phosphor particles are dispersed has its substantial thickness increased, the influence of variation in thickness of the luminescent layer becomes small, thus reducing emission unevenness caused by the variation in thickness of the luminescent layer. As the translucent base material, a resin or like materials may be used. As the resin, a resin such as an epoxy resin, an acrylic resin, a polyimide resin, a urea resin or a silicone resin may be used, and an epoxy resin or a silicone resin is preferably used.
The luminescent layer may be made by forming (sintering) the silicate phosphor.
The light-emitting semiconductor device preferably has a structure in which blue light emitted by the blue-light-emitting device passes through the luminescent layer so that the color of the fluorescence emitted by the phosphor is added to the color of the blue light, thereby emitting white light.
The inventive light-emitting semiconductor device may have any of the structures including the following members.
A first structure is a structure in which a substrate is further provided, the blue-light-emitting device is flip-chip mounted on the substrate, and the luminescent layer functions as a molding resin for molding the blue-light-emitting device.
In such a case, the substrate preferably includes a Zener diode.
A second structure is a structure in which a mount lead with a cup is further provided, the blue-light-emitting device is mounted in the cup, and the luminescent layer is provided within the cup.
A third structure is a structure in which a casing for placing the blue-light-emitting device therein is further provided, and the luminescent layer may be provided within the casing.
The light-emitting semiconductor device with such structures is implemented as a light-emitting semiconductor device emitting white light with a high luminous flux. The light-emitting semiconductor device can be fabricated through a relatively simple process, so that the fabrication yield enhances.
Among the light-emitting semiconductor devices having the first through third structures, the light-emitting semiconductor device with the first structure has the characteristic that the color unevenness is inherently smaller than those in the other light-emitting semiconductor devices with the second and third structures. Therefore, the light-emitting semiconductor device with the first structure is preferably used because the color unevenness in the light-emitting semiconductor device is further reduced so that the production yield further enhances.
The luminescent layer preferably has a substantial thickness in the range from 50 μm to 1000 μm, both inclusive, where the light extraction surface of the blue-light-emitting device is located.
If the substantial thickness of the luminescent layer is set within the range from 50 μm to 1000 μm, both inclusive, and more preferably within the range from 100 μm to 700 μm, both inclusive, the cross-sectional area of the silicate phosphor to be excited by the blue light increases, as compared to the case of the known YAG phosphor. Accordingly, the luminous intensity of the yellow light emitted by the silicate phosphor increases, and the light-emitting semiconductor device emits white light with excellent color tone by adding the colors the yellow light and of the blue light emitted by the blue-light-emitting device together. Moreover, as described above, since the luminescent layer has substantially no light absorption and attenuation factor, blue light emitted by a blue-light-emitting device either passes through the luminescent layer without being absorbed and attenuated or contributes to excitation of the phosphor, thus increasing the luminous intensity of the yellow light emitted by the silicate phosphor. Accordingly, if an optimum phosphor concentration (weight ratio between resin and phosphor: phosphor weight/(phosphor weight+resin weight)) is selected, the light-emitting semiconductor device emits white light with a luminous flux higher than that of the known light-emitting semiconductor device using the YAG-based phosphor.
As compared to the known light-emitting semiconductor device using the YAG-based phosphor, the substantial thickness of the luminescent layer increase largely. Therefore, even if surface unevenness in the substantial luminescent layer is large to some extent, the thickness of the entire luminescent layer is less affected by the surface unevenness, so that apparent thickness variation is reduced. As a result, emission unevenness caused by the variation in thickness of the luminescent layer is also reduced.
If the substantial thickness of the luminescent layer is smaller than the preferable thickness ranges, the cross-sectional area of the silicate phosphor to be excited by the blue light is small so that the substantial luminous efficacy of the phosphor is low. Accordingly, the light-emitting semiconductor device emits bluer light in which the emission from the blue-light-emitting device is dominant, resulting in that there may be cases where white light with excellent color tone cannot be obtained or a high luminous flux cannot be obtained. On the other hand, if the substantial thickness is larger than the thickness ranges, the cross-sectional area of the silicate phosphor to be excited by the blue light is large so that the substantial luminous efficacy of the phosphor is high but most of the blue light is absorbed in the phosphor to be converted into yellow/yellowish light. Accordingly, the light-emitting semiconductor device emits yellower light in which the yellow/yellowish emission from the silicate phosphor is dominant, resulting in that there may be cases where white light with excellent color tone cannot be obtained. Further, there may also be cases where a high luminous flux cannot be obtained because the phosphor particles are prone to be partially in contact with each other to cause blue light from the blue-light-emitting device to be more and more absorbed and attenuated.
In the known light-emitting semiconductor device using the YAG-based phosphor, if the luminescent layer is made thick as in the inventive light-emitting semiconductor device, the YAG-based phosphor has an extremely high luminous efficacy when irradiated with blue light under a phosphor concentration condition (10 to 80 wt. %) in the luminescent layer including a general silicate phosphor. Accordingly, only yellower emission in which light emitted by the YAG-based phosphor is dominant is obtained and the luminous flux also decreases. If the phosphor concentration is reduced so as to secure a desired color of light and to obtain such a thick luminescent layer, YAG-based phosphor particles are liable to disperse unevenly in a base material (a resin). This results in that the chromaticity and the luminance of the resultant emission vary largely and, in addition, the light distribution characteristics are prone to deteriorate. For this reason, the light-emitting semiconductor device has only a small commercial value.
As is explicitly shown in the case where phosphor particles are unevenly distributed in the base material and which is herein described using the micrographs in
The upper surface of a portion of the luminescent layer located at least on the light-extracting surface of the blue-light-emitting device is preferably flat and substantially parallel to the light-extracting surface.
Most of the blue-light-emitting devices are fabricated to have flat light-extracting surfaces (especially flat main light-extracting surfaces) because of the easiness of the fabrication. Therefore, if the surface of the luminescent layer is formed to be parallel to the light-extracting surface (especially the main light-extracting surface), the distance from the outer contour surface of the light-extracting surface to the outer contour surface of the luminescent layer, i.e., the thickness of the luminescent layer, is made substantially uniform in almost every part of the luminescent layer located on the light-extracting surface, so that the variation in thickness of the luminescent layer is further suppressed and, therefore, emission unevenness of the light-emitting semiconductor device is reduced.
The blue-light-emitting device may be provided in a plural presence and the luminescent layer may be provided to cover respective light-emitting surfaces of the plurality of blue-light-emitting devices.
An inventive light-emitting system is a light-emitting system including: a blue-light-emitting device emitting blue light; a luminescent layer including a yellow/yellowish phosphor which absorbs blue light emitted by the blue-light-emitting device to emit a yellow/yellowish fluorescence; and a supporter for supporting the blue-light-emitting device and the luminescent layer. The yellow/yellowish phosphor is a silicate phosphor containing, as a main component, at least one type of a compound expressed by the chemical formula:
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1).
The inventive light-emitting semiconductor device including the blue-light-emitting device and the luminescent layer exhibits small color unevenness, resulting in a high production yield and a low production cost. Accordingly, if a light-emitting system is configured using the light-emitting semiconductor device, the light-emitting semiconductor system not only has reduced color unevenness but also is fabricated at a low cost. Moreover, since such a light-emitting semiconductor device exhibits a luminous flux higher than that of the known light-emitting semiconductor device using the YAG-based phosphor, the luminous flux of the light-emitting system enhances.
The blue-light-emitting device may be provided in a plural presence and the luminescent layer may be provided to cover respective light-emitting surfaces of the plurality of blue-light-emitting devices.
In this description, various kinds of display systems using light-emitting semiconductor devices (e.g., LED information display terminals, LED traffic lights, LED stoplights of vehicles, and LED directional lights) and various kinds of lighting systems (e.g., LED interior/exterior lights, courtesy LED lights, LED emergency lights, and LED surface emitting sources) are broadly defined as light-emitting systems.
An inventive method for fabricating a luminescent layer of a light-emitting semiconductor device is a method for fabricating a light-emitting semiconductor device including: a blue-light-emitting device emitting light having a main emission peak in the wavelength range greater than 430 nm and less than or equal to 500 nm; and a luminescent layer including a yellow/yellowish phosphor which absorbs blue light emitted by the blue-light-emitting device to emit a fluorescence having a main emission peak in the wavelength range from 550 nm to 600 mm, both inclusive. The method includes the steps of: a) covering at least a light-extracting surface of the blue-light-emitting device with a phosphor paste including the yellow/yellowish phosphor which has an absolute specific gravity in the range from 3.0 to 4.65, both inclusive, and emits light having a main emission peak in the wavelength range from 560 nm to 600 nm, both inclusive, at room temperature, and with a resin which has an absolute specific gravity in the range greater than or equal to 0.8 and less than or equal to the absolute value of the yellow/yellowish phosphor; and b) curing the phosphor paste, thereby forming the luminescent layer. In the step a), a phosphor including, as a base material, a compound containing at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y, lanthanoid, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Zn, B, Al, Ga, In, Si, Ge, Sn and P and at least one element selected from the group consisting of O, S, Se, F, Cl and Br is used as the yellow/yellowish phosphor. The component does not include an element having a large specific gravity such as Cd.
In this manner, if a yellow/yellowish phosphor having an absolute specific gravity smaller than that of a YAG-based phosphor is used in the method for fabricating the luminescent layer by curing the phosphor paste including the yellow/yellowish phosphor and the resin, the difference in specific gravity between the resin (generally having an absolute value smaller than that of the phosphor except for special cases) and the phosphor is reduced. Thus, the phosphor is less liable to sediment in the phosphor paste by gravity before or during the curing of the phosphor paste, resulting in that the resultant luminescent layer has a structure in which the phosphor particles are dispersed substantially evenly throughout the resin or a like structure. In addition, since a phosphor containing no noxious Cd, preferably a phosphor including an oxide, is used, fabrication, handling, storage, control and the like therefor are easy.
In the step a), a yellow/yellowish phosphor having a particle size in the range from 0.5 μm to 30 μm, both inclusive, may be used.
Then, it is possible to obtain a luminescent layer exhibiting a high luminous intensity and having a structure in which phosphor particles are dispersed.
In the step a), a silicate phosphor containing, as a main component, at least one type of a compound expressed by the chemical formula
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1)
may be used as the yellow/yellowish phosphor.
It should be noted that the values a1, b1 and x are preferably in the ranges 0<a1≤0.2, 0≤b1≤0.7 and 0.005<x<0.1. A silicate phosphor having a composition within the preferable ranges and emitting a fluorescence with a main emission peak in the wavelength range from 560 nm to 600 nm, both inclusive, has an absolute specific gravity smaller than that of a YAG-based phosphor in general, i.e., in the range from 3.0 to 4.65, both inclusive. In addition, the silicate phosphor also serves as a yellow/yellowish phosphor which emits yellow/yellowish light when excited by blue light. Therefore, if a luminescent layer is formed using the silicate phosphor in combination with a resin (e.g., an epoxy resin) having an absolute specific gravity in the range greater than or equal to 0.8 and less than or equal to the absolute value of the yellow/yellowish phosphor, the luminescent layer is implementable as a luminescent layer exhibiting a high luminous intensity and having a structure in which phosphor particles are dispersed in an actual process. In the case where the value a1 is larger than the preferable range, as the value a1 increases, the absolute specific gravity of the silicate phosphor increases so that the phosphor particles are more liable to sediment in the phosphor paste and, as a result, it might be impossible to obtain a luminescent layer with a structure in which the phosphor particles are dispersed. This action is due to the fact that a Ba atom is heavier than a Sr atom.
Now, a relationship among the composition, the absolute specific gravity, and the main emission peak wavelength of a YAG-based phosphor is simply described. Though the absolute gravity of a YAG-based phosphor varies largely depending on the composition, especially the amount of Gd substituting Y, a YAG-based phosphor having a main emission peak in the wavelength range from 560 nm to 600 nm, both inclusive, under room temperature has a large substitution amount of Gd in general, resulting in having an absolute gravity greater than 4.55, greater, moreover, than 4.60, 4.65, and even exceeding 4.7. That is to say, such a YAG-based phosphor is heavy.
Ultra-fine particles including primary particles having an average particle size in the range from 1 nm to 100 nm, both inclusive, may be included in the phosphor paste and a luminescent layer may be formed by curing the phosphor paste. The sedimentation speed of the ultra-fine particles in a resin is extremely low and is almost zero. Therefore, in this manner, the ultra-fine particles suspended in the resin act in such a manner as preventing the sedimentation of the yellow/yellowish phosphor, so that the sedimentation speed of the yellow/yellowish phosphor decreases. As a result, a luminescent layer with a structure in which phosphor particles are dispersed is easily obtained.
In addition, the device may be configured such that blue light emitted by a blue-light-emitting diode passes through the luminescent layer so that the color of a (yellow/yellowish, red/reddish or green/greenish) fluorescence emitted by the phosphor is added to the color of the blue light, thereby emitting white light. Then, the colors of the blue light and the (yellow/yellowish, red/reddish or green/greenish) fluorescence emitted by the phosphor are added together as intended, thereby obtaining white light.
Examples of methods for suppressing the sedimentation of the phosphor particles while the phosphor paste is curing include the following methods.
A first method is a method for fabricating a light-emitting semiconductor device including the steps of a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles; and b) curing the phosphor paste while applying a vibration to the phosphor paste.
A second method is a method for fabricating a light-emitting semiconductor device including the steps of: a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles; and b) curing the phosphor paste while turning over the phosphor paste.
A third method is a method for fabricating a light-emitting semiconductor device including the steps of a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles; and b) curing the phosphor paste, wherein the steps a) and b) are performed a plurality of times.
A fourth method is a method for fabricating a light-emitting semiconductor device including the steps of: a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles and having a viscosity in the range from 1 Pa·S to 100 Pa·S, both inclusive; and b) curing the phosphor paste, wherein the steps a) and b) are performed a plurality of times.
A fifth method for fabricating a light-emitting semiconductor device including the steps of: a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles; and b) curing the phosphor paste with ultraviolet radiation.
A sixth method for fabricating a light-emitting semiconductor device including the steps of: a) covering a light-extracting surface of a blue-light-emitting device with a phosphor paste including a resin and phosphor particles; and b) curing the phosphor paste while agitating the phosphor paste.
Examples of methods for obtaining a light-emitting semiconductor device with a structure in which a maximum amount of phosphor particles are made close to the blue-light-emitting device include the following methods.
A first method is a method including the steps of: a) covering at least a light-extracting surface of a blue-light-emitting device which emits light having a main emission peak in the wavelength range greater than 430 nm and less than or equal to 500 nm, with a first phosphor paste including a base material of a translucent resin and phosphor particles including a yellow/yellowish phosphor; b) covering the first phosphor paste with a second phosphor paste including at least a translucent resin and containing a yellow/yellowish phosphor at a concentration lower than that in the first phosphor paste, after the step a) has been performed; and c) curing the first and second phosphor pastes. In the step a), as the yellow/yellowish phosphors, a silicate phosphor which is a yellow/yellowish phosphor absorbing light emitted by the blue-light-emitting device to emit light having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, and which contains, as a main component, at least one type of a compound expressed by the chemical formula
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1) is used.
A second method is a method including the steps of a) attaching phosphor particles including a yellow/yellowish phosphor to at least a light-extracting surface of a blue-light-emitting device which emits light having a main emission peak in the wavelength range greater than 430 nm and less than or equal to 500 nm; b) covering at least the light-extracting surface of the blue-light-emitting device with a translucent resin, after the step a) has been performed and c) curing the resin. In the step a), as the yellow/yellowish phosphor, a silicate phosphor which is a yellow/yellowish phosphor absorbing light emitted by the blue-light-emitting device to emit light having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, and which contains, as a main component, at least one type of a compound expressed by the chemical formula
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1) is used.
In this method, in the step a), the yellow/yellowish phosphor particles may be sprinkled on the blue-light-emitting device. Alternatively, in the step a), the blue-light-emitting device may be immersed in a suspension containing phosphor particles including a yellow/yellowish phosphor and a volatile solvent, and then the solvent may be evaporated.
A third method is a method including the steps of a) covering at least a light-extracting surface of a blue-light-emitting device which emits light having a main emission peak in the wavelength range greater than 430 nm and less than or equal to 500 nm, with a phosphor paste including a translucent resin and phosphor particles, which includes a yellow/yellowish phosphor and to whose surfaces positively charged substances are attached; and b) curing the phosphor paste. In the step a), as the yellow/yellowish phosphor, a silicate phosphor which is a yellow/yellowish phosphor absorbing light emitted by the blue-light-emitting device to emit light having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, and which contains, as a main component, at least one type of a compound expressed by the chemical formula
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4
(where 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1)
is used.
Hereinafter, a first embodiment of the present invention relating to a light-emitting semiconductor device and a method for suppressing color unevenness in the light-emitting semiconductor device will be described with reference to the drawings.
In each of the first through third exemplary light-emitting semiconductor devices shown in
A blue-light-emitting device according to the present invention may be a device selected from among a laser diode, a surface emitting laser diode, an inorganic electroluminescence device and an organic electroluminescence device, as well as the blue LED (blue-light-emitting diode) of this embodiment. However, in terms of increase in the output and the lifetime of the light-emitting semiconductor device, diodes such as a light-emitting diode, a laser diode and a surface emitting laser diode are superior to other devices.
The inventive light-emitting semiconductor device is a light-emitting semiconductor device configured by combining the blue LED 1 and the luminescent layer 3 containing the yellow/yellowish phosphor particles 2 that absorbs blue light emitted by the blue LED 1 to emit a fluorescence having an emission peak in the wavelength range from 550 nm to 600 nm, both inclusive. The yellow/yellowish phosphor particles 2 contained in the luminescent layer 3 is excited by part of the light from the blue LED 1 to produce a fluorescence with a wavelength different from that of the light from the blue LED. Accordingly, the color mixture of the fluorescence from the yellow/yellowish phosphor and the light from the blue LED that has been output and does not contribute to excitation of the yellow phosphor is produced, thereby allowing emission of white or whitish light.
Now, the yellow/yellowish phosphor particles 2 are a silicate phosphor containing, as a main component, a compound expressed by the following Chemical Formula (1):
(Sr1-a1-b1-xBaa1Cab1Eux)2SiO4 (1)
In Chemical Formula (1), the values a1, be and x are in the range 0≤a1≤0.3, 0≤b1≤0.8 and 0<x<1, respectively).
This silicate phosphor can be in the three kinds of crystal structures of an orthorhombic system, a monoclinic system and a hexagonal system, as will be described later in detail using experimental data. In the inventive light-emitting semiconductor device, it is sufficient for the yellow/yellowish phosphor to emit a fluorescence having a main emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, by absorbing blue light emitted by the blue LED 1. The crystal structure of the silicate phosphor may be any one of the orthorhombic system, the monoclinic system and the hexagonal system.
An experiment done by the present inventors shows that such a yellow/yellowish phosphor is limited to a silicate phosphor containing, as a main component, a compound expressed by the following Chemical Formula (2):
(Sr1-a1-b2-xBaa1Cab2Eux)2SiO4 (2)
In Chemical Formula (2), the values a1, b2 and x are in the ranges 0≤a1≤0.3, 0≤b2≤0.6 and 0<x<1, respectively. It is preferable that the values a1, b2 and x are in the ranges 0<a1≤0.2, 0<b2≤0.4 and 0.005<x<0.1, respectively. It is more preferable that the values a1, b2 and x are in the ranges 0<a1≤0.15, 0<b2≤0.3 and 0.01<x<0.05, respectively. It is most preferable that the values a1, b2 and x are in the ranges 0.01≤a1≤0.1, 0.001≤b2≤0.05 and 0.01<x≤0.02, respectively.
With a composition in which the values a1 and b2 in Chemical Formula (2) are smaller than the ranges mentioned above, the silicate phosphor is liable to have an unstable crystal structure and to include a monoclinic crystal structure, resulting in that the emission characteristics change depending on the operation temperature. On the other hand, with a composition in which these values are larger than the ranges, even if the crystal structure is an orthorhombic system, the phosphor emits greenish light, proving to be not a desirable yellow/yellowish phosphor but a green/greenish phosphor. Accordingly, even if the phosphor is combined with a blue LED, a white-light-emitting semiconductor device exhibiting an excellent color of light is not achieved. With a composition in which the amount of addition of Eu x is smaller than the range, the luminous intensity is low. With a composition in which the amount is larger than the range, there arises noticeably not only a problem that the luminous intensity is low because of concentration quenching (of luminescence) or self-absorption caused by Eu2+ ions but also a problem of thermal quenching that the luminous intensity decreases as the ambient temperature increases. The yellow/yellowish phosphor used in the present invention is preferably a silicate phosphor having an orthorhombic crystal structure because the silicate phosphor emits the yellow/yellowish light which is excellent in color purity and, therefore, a light-emitting semiconductor device emitting white light with excellent color can be provided. Part of Sr, Ba or Ca may be substituted with Mg or Zn to stabilize the crystal structure of the silicate phosphor or to enhance the luminous intensity.
To control the color of light emitted by the silicate phosphor, part of Si may be substituted with Ge. That is to say, the inventive light-emitting semiconductor device may be a light-emitting semiconductor device using a yellow/yellowish phosphor containing, as a main component, a compound expressed by the following Chemical Formula (3):
(Sr1 a1 b1 xBaa1Cab1Eux)2Si1 zGezO4 (3)
where the values a1, b1, x and z are in the ranges 0≤a1≤0.3, 0≤b1≤0.8, 0<x<1 and 0≤z<1 (preferably 0≤z≤0.2, respectively). If part of Si is substituted with Ge, the tendency of the luminous intensity to greatly decrease is observed. However, if at least the substitution amount of Ge is 20 atomic percent (at. %) or more, the main emission peak shifts to shorter wavelengths, thus obtaining emission of greenish light. To hold luminous intensity, the substitution amount of Ge z is preferably as small as possible and the value z is preferably within the range lower than 0.2.
Further, a red phosphor that absorbs light such as blue light emitted by the blue LED or yellow/yellowish light emitted by the silicate phosphor and has a main emission peak in the red wavelength range greater than 600 nm and less than or equal to 660 nm may be additionally used in order to compensate for the red spectrum of the light emitted by the light-emitting semiconductor device. A green phosphor that absorbs light such as blue light from the blue LED and has a main emission peak in the green wavelength range greater than or equal to 500 nm and lower than 550 nm where the luminous efficacy is high may be also additionally used to enhance the luminous flux.
Materials for such red and green phosphors are not limited to the materials used in this embodiment. Such a red or green phosphor may be a phosphor made of an inorganic compound or a phosphor made of an organic compound.
Usages of such red and green phosphors are not limited to the method of this embodiment so long as the light-emitting semiconductor device further includes these phosphors (luminescence materials). These phosphors may be included in a luminescent layer or may be disposed apart from the luminescent layer so long as each of the phosphors absorbs the blue light to emit red or green light and the blue light passes through at least the luminescent layer.
Examples of the red phosphor include: phosphors such as a CaS:Eu2+ phosphor and an SrS:Eu2+ phosphor known as a cathodoluminescence material or an electroluminescence material; a rare-earth complex or a resin structure including the rare-earth complex disclosed in, for example, Japanese Laid-Open Publications Nos. 11-246510 and 2000-63682; and an LiEuW2O8 phosphor disclosed in, for example, Japanese Laid-Open Publication No. 2001-267632.
The use of such a red phosphor increases the intensity of red emission spectrum of the light-emitting semiconductor device, especially a white-light-emitting semiconductor device, resulting in enhancement of R9 recited in JIS Z 8726-1990 or color gamut ratio Ga recited in JIS Z 8726-1990 for reference, which are known as special color rendering indices representing faithfulness toward red in the field of illumination, thus allowing the light-emitting semiconductor device to exhibit the color of light in which these indices are high.
Examples of the green phosphor include: an SrGa2S4: Eu2+ phosphor known as a cathodoluminescence material or an electroluminescence material; and a silicate phosphor emitting a fluorescence having an emission peak in the wavelength range from 500 nm to 600 nm, both inclusive, and containing, as a main component, a compound expressed by the following Chemical Formula (4):
(Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 (4)
In the formula, the values a3, b3 and x are in the ranges 0≤a3≤1, 0≤b3≤1 and 0<x<1, respectively.
This (Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 silicate phosphor is a phosphor different from the above-described silicate phosphor emitting yellow/yellowish light, only in composition and crystal structure. Accordingly, the (Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 silicate phosphors have similar properties to those of the yellow/yellowish-light-emitting silicate phosphor. Therefore, the use of green-light-emitting silicate phosphor in combination with the yellow-light-emitting silicate phosphor is more preferable in terms of not only light-emitting semiconductor device characteristics but also the fabrication thereof.
To provide a light-emitting semiconductor device emitting a desired color of light, a plurality of such silicate phosphors having mutually different compositions and each emitting yellow/yellowish light having an emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, may be included in a luminescent layer. The silicate phosphors are phosphors which can emit light covering a large area of the yellow/yellowish wavelength range by changing the compositions. Therefore, if a plurality of types of such silicate phosphors are combined, it is possible to enlarge the color expression range of light which is emitted by the light-emitting semiconductor device, especially a light-emitting semiconductor device emitting white or whitish light, and determined by adding the colors of blue light from a blue LED and of yellow/yellowish light from the silicate phosphors.
In terms of color control for light, especially for white or whitish light, emitted by the light-emitting semiconductor device, it is effective to include, in a luminescent layer, at least one type of silicate phosphor containing a component expressed by Chemical Formula (4) as a main component and differing from a yellow/yellowish phosphor in composition. The silicate phosphor is a phosphor that emits light when excited by blue light with any of the composition ranges for the values a3 and b3 and, moreover, that has an emission peak wavelength variable in the wide wavelength range of about 505 to 598 nm by changing the composition of the phosphor. If such a phosphor is additionally included in the luminescent layer, the light-emitting semiconductor device emits light by adding the colors of blue light emitted by the blue LED and yellow/yellowish light emitted by the yellow/yellowish-light-emitting silicate phosphor emitting light and at least one of blue-green, green, yellow and orange lights emitted by an (Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 together, i.e., adding at least three colors together. Therefore, it is possible to enlarge the range of color control for light emitted by the light-emitting semiconductor device.
The light-emitting semiconductor device shown in any one of
It is sufficient for the silicate phosphor to have a particle size of 0.1 μm to 100 μm, both inclusive, in an evaluation of particle distribution with a laser diffraction particle size analyzer (e.g., LMS-30 produced by Seishin Enterprise Co., Ltd.). However, in terms of ease of the synthesis, availability of a phosphor or formability of a luminescent layer, the particle size preferably ranges from 0.5 μm to 30 μm, both inclusive, more preferably from 1 μm to 20 μm, both inclusive, and still more preferably from 2 μm to 10 μm, both inclusive. With respect to the particle-size distribution, it is sufficient for the silicate phosphor to include no particles smaller than 0.01 μm or greater than 1000 μm. However, for the same purpose as for the particle size, the particle-size distribution in the silicate phosphor is preferably close to the normal distribution in the particle-size range from 1 μm to 50 μm, both inclusive.
Such a silicate phosphor can be fabricated by a synthesizing method described in, for example, the above-mentioned literature (J. Electrochemical Soc. Vol. 115, No. 11(1968) pp. 1181-1184). A method for fabricating a silicate phosphor for the light-emitting semiconductor device of this embodiment will be described later. Hereinafter, properties of a silicate phosphor will be described in further detail.
As shown in
If the silicate phosphor has a composition in which the values a1, b1, b2 and x are within the respective given ranges shown in Formulas (1) and (2), the excitation light and emission spectra thereof are similar to those shown in
Now, characteristics of a luminescent layer using the silicate luminescent layer are described.
The exemplary excitation spectrum and emission spectrum shown in
Comparison in excitation spectrum between the silicate phosphor and the YAG-based phosphor shown in
If a luminescent layer is formed using the above-described silicate phosphor and a resin, distribution of phosphor particles in the luminescent layer is small, as compared to a known luminescent layer using a YAG-based phosphor. If a light-emitting semiconductor device is configured by using a YAG-based phosphor, phosphor particles are in contact with each other in a luminescent layer, thus arising a problem that the intensity of the resultant white or whitish light is low, as described above. Such a problem of low intensity because of this reason is caused not only in the case where a YAG-based phosphor is used but also in any case where the light-emitting semiconductor device has a luminescent layer in which phosphor particles are in contact with each other.
On the other hand, if conditions for forming a luminescent layer are selected as those for the light-emitting semiconductor device of this embodiment, phosphor particles are relatively evenly dispersed in the luminescent layer, thus obtaining a light-emitting semiconductor device that emits light with small color unevenness. The reason why the use of the silicate phosphor of this embodiment reduces distribution unevenness of the phosphor particles in the luminescent layer has been minutely investigated but has not clarified completely yet. However, the reduction in distribution unevenness of the phosphor particles definitely relates to at least the fact that the difference in specific gravity between the phosphor and the resin is smaller than that between the YAG-based phosphor and the resin.
Hereinafter, the point where the luminescent layer in the light-emitting semiconductor device of this embodiment has a structure in which phosphor particles are relatively evenly dispersed throughout a base material (a scattering structure) will be described with reference to
In the luminescent layer 3 shown in
The luminescent layer 3 of the inventive light-emitting semiconductor device may include a phosphor in addition to the yellow/yellowish phosphor or may include a substance other than a phosphor. Moreover, the luminescent layer 3 may contain a plurality of types of such yellow/yellowish phosphors.
In the light-emitting semiconductor device of this embodiment, so long as the luminescent layer 3 has a structure in which the yellow/yellowish phosphor particles 2 are dispersed in the base material 13 as shown in
The smaller the size of the yellow/yellowish phosphor particles 2 is, the more dispersed the particles in the luminescent layer 3 are. However, since small phosphor particles have a large specific surface area (of particles), the ratio of the surface area of the particles where a lot of lattice defects are present is high with respect to the volume of the phosphor particles, so that the luminous intensity of light from the luminescent layer 3 decreases. On the other hand, if the phosphor particles are large in size, the yellow/yellowish phosphor particles 2 readily sediment by gravity during the formation of the luminescent layer 3, so that the luminescent layer 3 has a structure in which the phosphor particles are less dispersed. In view of this, the particle size of the yellow/yellowish phosphor is preferably in the above-described range (i.e., the range from 0.5 μm to 30 μm, both inclusive), more preferably from 1 μm to 25 μm, both inclusive, and still more preferably from 3 μm to 20 μm, both inclusive.
A material for the base material 13 is not limited to the material described in this embodiment so long as the luminescent layer 3 has a structure in which phosphor particles are dispersed as shown in
In the case where the base material 13 is a resin, as the absolute specific gravity of the resin comes close to the absolute specific gravity of the yellow/yellowish phosphor particles 2, the phosphor particles are tend to disperse more and more in the luminescent layer 3. As will be described later, the absolute specific gravity of a resin is smaller than that of the yellow/yellowish phosphor particles 2 in general, the absolute specific gravity of the resin is preferably as large as possible within the range lower than the absolute specific gravity of the yellow/yellowish phosphor particles 2.
If the absolute specific gravity of the resin is small, the yellow/yellowish phosphor particles 2 readily sediment by gravity during the formation of the luminescent layer 3, so that the phosphor particles are less readily to disperse in the luminescent layer 3. In view of this, the absolute specific gravity of the resin is preferably set in the range greater than or equal to 0.8 and less than or equal to the absolute specific gravity of the phosphor particles, more preferably in the range greater than or equal to 1.0 and less than or equal to the absolute specific gravity of the phosphor particles, and still more preferably in the range greater than or equal to 1.5 and less than or equal to the absolute specific gravity of the phosphor particles
According to “Plastic Data Handbook” (edited by Kimimasa ITO and published by Kogyo Chosakai Publishing Co. Ltd.) or “Nonmetallic Material Data Book” (published by Japanese Standards Association), for example, the absolute specific gravity of an epoxy resin is between 1.0 and 2.1, inclusive, the absolute specific gravity of an acrylic resin is between 1.0 and 1.4, inclusive, the absolute specific gravity of a polyimide resin is between 1.3 and 1.5, inclusive, the absolute specific gravity of a urea resin is about 1.5 and the absolute specific gravity of a silicone resin is between 1.7 and 2.0, inclusive.
In each of the exemplary light-emitting semiconductor devices shown in
General Fabrication Method
Concrete examples for fabricating an inventive light-emitting semiconductor device will be described in detail later. Now, a summary of a method for fabricating a luminescent layer 3 having a structure in which phosphor particles are dispersed and preferred embodiments thereof are described.
A luminescent layer 3 with a structure in which phosphor particles are dispersed can be formed by placing a phosphor paste, in which yellow/yellowish phosphor particles 2 having an absolute specific gravity within a given range are dispersed in a base material 13 having an absolute specific gravity within a given range, in a position in a light-emitting semiconductor device through a process such as injection or application, and then by curing the phosphor paste.
The phosphor paste can be fabricated by weighing and mixing the yellow/yellowish particles 2 and the base material 13 such as a resin such that the phosphor paste has a given phosphor concentration. To mix these materials, various techniques may be used. Examples of the techniques include mixing using a mortar, stirring using an agitator and mulling using a roller.
In the mixing, the weight percentage of the yellow/yellowish phosphor particles 2 with respect to the base material 13 (i.e., the phosphor concentration) is preferably in the range from 10 wt % to 80 wt %, both inclusive, and more preferably in the range from 20 wt % to 60 wt %, both inclusive. If the phosphor concentration is lower than the ranges, the luminescent layer 3 exhibits weak emission of the yellow/yellowish phosphor so that the light-emitting semiconductor device configured by using the luminescent layer 3 emits bluer light, resulting in that it is difficult to obtain white light with excellent color tone. On the other hand, if the phosphor concentration is higher than the range, the luminescent layer 3 exhibits strong emission of the yellow/yellowish phosphor so that the light-emitting semiconductor device configured by using the luminescent layer 3 emits yellower light, resulting in that is difficult to obtain white light with excellent color tone.
In the inventive method for fabricating the luminescent layer, a technique for curing the phosphor paste is not limited to a specific technique. The phosphor paste may be cured by: using a material that cures by mixing two liquids such that the curing due to mixing of the two liquids occurs in the phosphor paste; heating the phosphor paste using a thermosetting material; or irradiating the paste with light using a photo-curing material. The luminescent layer 3 can be obtained with any one of the curing techniques for the phosphor paste.
To form the luminescent layer 3 in which phosphor particles are dispersed, it is preferable to suppress the sedimentation speed of the yellow/yellowish phosphor particles 2 in the base material 13.
Hereinafter, the sedimentation speed of phosphor particles being sedimenting in a solvent will be described for reference. According to Stokes' low, a ball having a radius r (unit: m) and a density ρ2 is being sedimenting in a fluid having a density ρ1 and a viscosity coefficient η (i.e., viscosity, unit: Pa·s or P (poise)) at a sedimentation speed μ (m/s) expressed by the following equation (5):
μ={2×r2×(ρ2−ρ1)×g}/(9×η) (5)
In Equation (5), g indicates a gravitational acceleration (unit: m·s−2).
Therefore, qualitatively, the sedimentation speed of phosphor particles being sedimenting in a resin as a solvent decreases as the particle size of the phosphor particles decreases, the speed also decreases as the difference in specific gravity between the phosphor particles and the resin narrows, and also decreases as the viscosity of the resin increases.
From Stokes' law described above, it is possible to reduce the sedimentation speed of the yellow phosphor 3 in the resin by using the following measures 1 through 4.
In the inventive method for fabricating the luminescent layer, each of the absolute specific gravity of the yellow/yellowish phosphor particles 2 that are limited in main emission peak wavelength range and in element and the absolute specific gravity of the resin are limited within a given range. As a preferred embodiment, the particle size of the yellow/yellowish phosphor is further limited to a given range. As a more preferred embodiment, the kind and composition of the yellow/yellowish phosphor are limited.
First, as the yellow/yellowish phosphor particles 2, used is a phosphor containing no Cd (cadmium) and emitting light having a main emission peak wavelength in the range from 560 nm to 600 nm, both inclusive, preferably in the range greater than 560 nm and less than or equal to 600 nm, and more preferably in the range from 565 nm to 600 nm, both inclusive, under room temperature. Next, the absolute specific gravity of the yellow/yellowish phosphor particles 2 is limited within the range from 3.0 to 4.65, both inclusive, preferably within the range from 3.0 to 4.60, both inclusive, and more preferably within the range greater than or equal to 3.0 and less than 4.55. In addition, the absolute specific gravity of the resin is limited within the range greater than or equal to 0.8 and less than or equal to the absolute specific gravity of the yellow/yellowish phosphor, preferably within the range greater than or equal to 1.0 and less than or equal to the absolute specific gravity of the yellow/yellowish phosphor, and more preferably within the range greater than or equal to 1.5 and less than or equal to the absolute specific gravity of the yellow/yellowish phosphor.
In this way, the difference in specific gravity between the yellow/yellowish phosphor particles 2 and the resin narrows so that the sedimentation speed of the phosphor particles in the resin decreases, as indicated by Stokes' low in Equation (5), resulting in that the luminescent layer with a structure in which the phosphor particles are dispersed is easily formed.
Especially, examples of yellow/yellowish phosphors containing no Cd include a phosphor including, as a base material, a compound containing at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Sc, Y, lanthanoid, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Zn, B, Al, Ga, In, Si, Ge, Sn and P and at least one element selected from the group consisting of O, S, Se, F, Cl and Br. These elements are relatively less noxious.
The reason why the main peak wavelength of the yellow/yellowish phosphor particles 2 is limited within the range from 560 nm to 600 nm, both inclusive, is to obtain white light having a desired color tone. The reasons why the absolute specific gravity of the resin is limited within the above-mentioned ranges and why the phosphor containing no Cd is exclusively used have been already explained.
In the inventive method for fabricating the light-emitting layer of the light-emitting semiconductor device, the yellow/yellowish phosphor particles 2 are not specifically limited in kind basically so long as the yellow/yellowish phosphor particles 2 contain no Cd, exhibits a main emission peak wavelength in the range from 560 nm to 600 nm, both inclusive, under room temperature and has an absolute specific gravity in the range from 3.0 to 4.65, both inclusive. The yellow/yellowish phosphor particles 2 may or may not be the silicate phosphor particles described above.
On the other hand, none of the known light-emitting semiconductor devices uses, as phosphor particles, such light yellow/yellowish phosphor particles 2 which contain no noxious substance, emit yellow/yellowish light when excited by blue light, and have an absolute specific gravity in the ranges described in this embodiment, so that the formation of the luminescent layer for the known devices requires a yellow-light-emitting YAG-based phosphor having a large absolute specific gravity. The yellow-light-emitting YAG-based phosphor particles have an absolute specific gravity in the range greater than 4.65 and less than or equal to about 4.98. The spectrum of emission from the yellow-light-emitting YAG-based phosphor particles shifts to longer wavelengths, as the absolute specific gravity thereof increases. Therefore, it is difficult for the known light-emitting devices to obtain excellent characteristics which are obtained in the light-emitting device of this embodiment.
In a preferred embodiment of the present invention, the particle size of the yellow/yellowish phosphor particles 2 is limited within the range from 0.5 μm to 30 μM, both inclusive, preferably within the range from 1 μm to 25 μm, both inclusive, and more preferably within the range from 3 μm to 20 μm, both inclusive. The reason why the particle size of the yellow/yellowish phosphor particles 2 is limited in this preferred embodiment has been already explained.
In a further preferred embodiment, a silicate phosphor containing, as a main component, a compound expressed by Chemical Formula (1), i.e., a compound expressed by (Sr1-a1-b1-xBaa1Cab1Eux)2SiO4, is used as the yellow/yellowish phosphor particles 2. Although the absolute specific gravity of the silicate phosphor varies to some extent depending on the composition, the absolute specific gravity of the yellow/yellowish phosphor particles 2 is easily set within the range from 3.0 to 4.65, both inclusive, thereby allowing a luminescent layer having a structure in which phosphor particles are dispersed to be formed easily. The specific gravity of the silicate phosphor containing a compound expressed by Chemical Formula (1) as a main component increases, as the substitution amount of Ba increases, while decreasing as the substitution amount of Ca increases.
Now, the absolute specific gravities of phosphors are supplementary described. True density measurements of phosphors by constant volume expansion with He gas replacement method using a Multivolume Pycnometer 1305 produced by Micromeritics Instrument Co. show that the absolute specific gravities of a YAG-based phosphor ((Y0.7Gd0.28Ce0.02)3Al5O12: main emission peak wavelength of 565 nm), a silicate phosphor ((Ba0.05Sr0.93Eu0.02)2SiO4 main emission peak wavelength of 575 nm) and a silicate phosphor containing a smaller amount of Si and having a composition different from the former silicate phosphor ((Ba0.24Sr0.74Eu0.02)2SiO4: main emission peak wavelength of 559 nm), are 4.98, 4.53 and 4.67, respectively (measurement accuracy: ±1%). As an example, with respect to the phosphor which emits light having a main emission peak around 565 nm, it was proved that the absolute specific gravity of the silicate phosphor is smaller than that of the YAG-based phosphor by about 10%.
Now, the viscosities of a resin and a phosphor paste are described. The inventive method for fabricating a luminescent layer of a light-emitting semiconductor device is not limited to fabrication methods which will be described later. However, if the viscosities of a resin and a phosphor paste are too low, phosphor particles sediment by gravity so that a structure in which the phosphor particles disperse in the resin cannot be achieved, as described above. On the other hand, if the viscosity of the resin is too high, there occurs a disadvantage that handling the light-emitting semiconductor device is cumbersome in a fabrication process. In view of these aspects, each of the viscosities of the resin and phosphor is in the range from 0.01 Pa·s to 10 Pa·s, both inclusive, preferably in the range from 0.03 Pa·s to 3 Pa·s, both inclusive, and more preferably in the range from 0.1 Pa·s to 1 Pa·s, both inclusive. However, the viscosity of a liquid fluid such as a resin or a phosphor paste varies depending on temperature and pressure, i.e., decreases as the temperature increases while increasing as the pressure increases. Therefore, it is difficult to define the viscosity simply. The viscosity of the resin or the phosphor paste may be adjusted within the ranges described above by adjusting conditions including pressure and temperature during the fabrication.
In the inventive method for forming the luminescent layer of the light-emitting semiconductor device, the phosphor paste may be formed by curing with ultra-fine particles whose primary particles have an average particle size in the range from 1 nm to 100 nm, both inclusive, preferably in the range from 3 nm to 50 nm, both inclusive, included in the phosphor paste.
As expressed by Equation (5), the sedimentation speed of ultra-fine particles with an extremely small particle radius is extremely low in a phosphor paste. Accordingly, if such ultra-fine particles are included in the phosphor paste, the ultra-fine particles, which sediment extremely slowly, act in such a manner as preventing sedimentation of the yellow/yellowish phosphor particles 2. As a result, by adding the ultra-fine particles to the phosphor paste, the sedimentation speed of the yellow/yellowish phosphor particles 2 in the phosphor paste decreases, so that the luminescent layer 3 having a structure in which the phosphor particles are dispersed in the resin is easily obtained.
Examples of such ultra-fine particles include a silicon dioxide powder known by the name of Aerosil (Degussa Co., Ltd.: Germany). Materials for ultra-fine particles which may be added to the phosphor paste is not limited to silicon dioxide and may be an ultra-fine particle material whose primary particles have an average particle size in the range from 1 nm to 100 nm, both inclusive. Instead of silicon dioxide, aluminum oxide, for example, may be used as the ultra-fine particle material.
Ultra-fine particles having a particle size of about 5 nm or less cannot be measured with the laser diffraction particle size analyzer as mentioned above. Therefore, the particle sizes (diameters) of ultra-fine particles are actually measured based on the object observed by an electron microscope observation, thereby defining an average value of the particle sizes as the average size of the primary particles.
As described above, with the method for forming the luminescent layer of the light-emitting semiconductor device, the luminescent layer 3 having a structure in which phosphor particles are dispersed is formed. The light-emitting semiconductor device including the luminescent layer having the structure in which phosphor particles are dispersed achieves remarkable effects with the following actions.
Specifically, such a luminescent layer contains substantially neither light absorption factor nor light scattering factor. Therefore, as compared to the known luminescent layer in which phosphor particles are in contact with each other, for example, phosphor particles are less likely to be in contact with each other, or even if these particles are in contact with each other, the contact area is largely reduced, so that the luminescent layer has substantially no light absorption and attenuation factor. Accordingly, the luminescent layer exhibits improved light transmissivity, thus allowing blue light emitted by a blue LED to pass through the luminescent layer without being absorbed and attenuated or to contribute to excitation of the phosphor. In addition, since the luminescent layer is in the state that the entire surface of the phosphor particles can be irradiated with the blue light, the cross-sectional area of the phosphor particles to be excited increases substantially, so that the phosphor particles in the luminescent layer emit light effectively. Part of the blue light which is applied to the phosphor particles but does not contribute to the excitation of the phosphor is reflected off the surfaces of the phosphor particles and then emitted as blue light to the outside of the luminescent layer. Since blue LEDs of the same type emit blue light with the same output, in a white-light-emitting semiconductor device that obtains white light by adding the colors of blue light emitted by a blue LED and yellow light emitted by a yellow phosphor together, the luminescent layer having fewer light absorption and attenuation factors and using a phosphor having a high internal quantum efficiency can exhibit a high luminous flux, even if the luminescent layer is made of a phosphor material having a low luminous efficacy (external quantum efficiency) in response to excitation by the blue light.
If the luminescent layer of the light-emitting semiconductor device of this embodiment and the known luminescent layer have the same surface area (e.g., the area of the uppermost surface of the luminescent layer 3 in the light-emitting semiconductor device shown in
Now, an embodiment of a light-emitting system according to the present invention is described with reference to the drawings.
Various kinds of displaying systems using light-emitting semiconductor devices (e.g., LED information display terminals, LED traffic lights, LED stoplights of vehicles and LED directional lights) and various kinds of lighting systems (e.g., LED interior/exterior lights, courtesy LED lights, LED emergency lights, and LED surface emitting sources) are herein defined broadly as light-emitting systems.
As shown in
The lighting system shown in
In the first exemplary lighting system, the color temperature is preferably in the range from 2000 K to 12000 K, both inclusive, more preferably in the range from 3000 K to 10000 K, both inclusive, and still more preferably in the range from 3500 K to 8000 K, both inclusive. However, the lighting system as the inventive light-emitting system is not limited to these color temperature ranges.
As shown in
As is the first exemplary lighting system, the image displaying system as an example of the light-emitting system is preferably configured using the light-emitting semiconductor devices 11 described in the first embodiment. Instead of the inventive light-emitting semiconductor devices, a device utilizing an LED which emits light such as blue, green, yellow or red light and a luminescent layer in combination may be used, for example. The color of light emitted by the light-emitting semiconductor devices 11, the size and the number of the devices 11, the shape of a light-emitting portion thereof, and the arrangement of the light-emitting semiconductor devices 11 are not specifically limited. In addition, external shape thereof is not specifically limited.
As shown in
The pattern displayed by the pattern displaying system is not limited to the numeral shown in
As is the first exemplary lighting system, the pattern displaying system as an example of the light-emitting system is preferably configured using the light-emitting semiconductor devices 11 described in the first embodiment. Instead of the inventive light-emitting semiconductor devices, a device utilizing an LED which emits light such as blue, green yellow or red light and a luminescent layer in combination may be used. The color of light emitted by the light-emitting semiconductor devices 11, the size and the number of the devices 11, the shape of a light-emitting portion thereof, and the arrangement of the light-emitting semiconductor devices 11 are not specifically limited. In addition, the external shape thereof is not specifically limited.
The light-emitting systems as shown in
If light-emitting semiconductor devices having substantially flat pixel surfaces are used for configuration of a light-emitting system, it is possible to obtain a light-emitting system whose entire light-emitting surface is substantially flat, e.g., a displaying system having a flat display surface or a surface-emitting lighting system, thus providing an image displaying system exhibiting excellent image quality or a well-designed lighting system.
In the case where the inventive light-emitting system is a lighting system or a displaying system, for example, the use of a light-emitting semiconductor device having a structure as described in the first embodiment suppresses color unevenness in the light-emitting system. The light-emitting semiconductor device of the first embodiment exhibits small color unevenness, resulting in a high production yield and a low production cost. That is to say, if the light-emitting system is configured using the light-emitting semiconductor device of the first embodiment, color unevenness as the light-emitting system is reduced and, in addition, the light-emitting system is fabricated at a low cost. Moreover, since the light-emitting semiconductor device of the first embodiment exhibits a luminous flux higher than that of a known light-emitting semiconductor device using a YAG-based phosphor, the luminous flux of the entire light-emitting system improves.
In this description, various kinds of display systems using light-emitting semiconductor devices (e.g., LED information display terminals, LED traffic lights, LED stoplights of vehicles, and LED directional lights) and various kinds of lighting systems (e.g., LED interior/exterior lights, courtesy LED lights, LED emergency lights, and LED surface emitting sources) are broadly defined as light-emitting systems.
Embodiment Relating to Method for Fabricating Light-Emitting Semiconductor Device
(Method for Fabricating Silicate Phosphor)
A method for fabricating a silicate phosphor for use in the inventive light-emitting semiconductor device is not limited to a fabrication method that will be described below. The silicate phosphor is fabricated by, for example, the following method.
The silicate phosphor can be obtained through the following processes, for example,
(First Process: Weighing and Blending of Phosphor Materials)
First, phosphor materials are weighed and blended. As the phosphor materials, various kinds of powders such as alkaline-earth metal compounds, silicon compounds and europium compounds may be used. Examples of the alkaline-earth metal compounds include alkaline-earth metal carbonates (strontium carbonate, barium carbonate and calcium carbonate), nitrates (strontium nitrate, barium nitrate and calcium nitrate), hydroxides (strontium hydroxide, barium hydroxide and calcium hydroxide), oxides (strontium oxide, barium oxide and calcium oxide), nitrates (strontium nitrate, barium nitrate and calcium nitrate), oxalates (strontium oxalate, barium oxalate and calcium oxalate). Halides (e.g., strontium chloride, barium chloride, calcium chloride, strontium fluoride, barium fluoride, calcium fluoride, strontium bromide, barium bromide and calcium bromide) may also be used. Examples of the silicon compounds include oxide such as silicon dioxide and silicon oxide. However, nonoxide such as silicon nitride may also be used under some conditions. To enhance the reactivity between the phosphor materials, silicon dioxide of an ultra-fine power such as an ultra-fine-powdery silica known by the name of “Aerosil” produced by Degussa Co., Ltd. (Germany) is preferably used. Examples of the europium compounds include europium oxide, europium fluoride and europium chloride. As a germanium material for the Ge-containing phosphor mentioned above, germanium compound such as germanium oxide may be used.
In the first process, these alkaline-earth metal compound, silicon compound and europium compound are weighed and blended such that the phosphor has a desired composition of elements such as alkaline-earth metal, silicon and europium.
To enhance the reactivity between the phosphor materials, a phosphor material or a temporary or primary fired phosphor material mixed with a flux may be used. As the flux, various kinds of halides and boron compounds may be used. Examples of the halides include strontium fluoride, barium fluoride, calcium fluoride, europium fluoride, ammonium fluoride, lithium fluoride, sodium fluoride, potassium fluoride, strontium chloride, barium chloride, calcium chloride, europium chloride, ammonium chloride, lithium chloride, sodium chloride and potassium chloride. Examples of the boron compounds include boric acid, boric oxide, strontium borate, barium borate and calcium borate. In the compound used as the flux, the number of moles is between 0.0001 and 1, both inclusive, and normally between 0.001 and 0.3, both inclusive, with respect to one mole of the phosphor.
(Second Process: Mixing of Phosphor Materials)
Next, the phosphor materials that have been weighed and blended to have specified mole fractions or weight percentages in the first process are mixed, thereby obtaining a phosphor material mixture. Various techniques may be used to mix the phosphor materials. Examples of mixing include mixing using a mortar, mixing using a ball mill, mixing using a V-shaped mixer, mixing using a cross rotary mixer, mixing using a jet mill and mixing using an agitator, all of which are well-known techniques. Dry mixing for mixing only the phosphor materials without using any solvent or wet mixing for adding the phosphor materials to a solvent such as water or an organic solvent so that the phosphor materials are spread and mixed in the solvent may be used as a method for the mixing. Ethanol or methanol may be used as the organic solvent. In the case of the dry mixing, the suspension made of the phosphor materials and the solvent is generally filtered using, for example, a Buchner filter, to obtain a phosphor material mixture, and then the filtered phosphor material mixture is dried at a temperature of about 60 to 200° C. for several to dozens of hours with, for example, a dryer, thereby obtaining a phosphor material mixture.
(Third Process: Firing of Phosphor Material Mixture)
Then, the phosphor material mixture is fired by the following procedure. A heater such as an electric furnace or a gas furnace is used for the firing. The heater is not specifically limited in type and may be of any type so long as the phosphor material mixture can be fired at a desired temperature in a desired atmosphere for a desired period of time. Examples of the electric furnaces as the heater include a tubular atmospheric furnace, a box-type controlled atmospheric furnace, a conveyor belt furnace, a roller-hearth furnace and a tray pusher continuous furnace. In general, the phosphor material mixture is put in a firing vessel such as a crucible or a boat with a lid put on the firing vessel in some cases, and then the phosphor material mixture is heated together with the firing vessel. Alternatively, only the phosphor material mixture may be fired. The firing vessel may be made of platinum, quartz, alumina, zirconia, magnesia, silicon carbide, silicon nitride, ceramic or carbon, or the firing vessel may be made by mixing these materials if necessary.
The silicate phosphor can be fabricated so long as the firing temperature is in the range from 800° C. to 1600° C., both inclusive. If the firing temperature is higher than the temperature range, phosphor particles are fired or dissolved, so that it is difficult to obtain a powdery silicate phosphor. On the other hand, if the firing temperature is lower than the temperature range, it is difficult to obtain intensive emission of light from the phosphor. To obtain a powdery silicate phosphor exhibiting a higher luminous efficacy, the firing temperature is preferably in the range from 1000° C. to 1500° C., both inclusive, more preferably in the range from 1100° C. to 1450° C., both inclusive, and still more preferably in the range from 1200° C. to 1400° C., both inclusive.
It is sufficient for the firing time to be in the range from 10 minutes to 1000 hours, both inclusive. However, to increase the efficiency in fabrication or to enhance the quality of the phosphor, for example, the firing time is preferably in the range from 30 minutes to 500 hours, both inclusive, and more preferably in the range from 1 hour to 100 hours, both inclusive. It is not specifically limited how many times the firing process is performed. However, to enhance the efficiency in fabricating the phosphor, the firing process is preferably performed less frequently and is most preferably performed only once.
The firing atmosphere may be freely selected from among air, a low-pressure atmosphere, a vacuum atmosphere, an inert-gas atmosphere, a nitrogen atmosphere, an oxygen atmosphere, an oxidizing atmosphere and a reducing atmosphere. However, since Eu2+ ions need to be formed as a luminescent center in the phosphor, it is necessary to perform firing in an atmosphere in which at least Eu2+ ions can be formed in the phosphor at the final stage or near final stages of firing. As this atmosphere, a reducing atmosphere using a mixed gas of nitrogen and hydrogen or using carbon monoxide, especially an ambient using a mixed gas of nitrogen and hydrogen, is preferably used for the purposes of simplifying the apparatus, reducing the cost thereof, and easily handling gases or materials for the atmosphere. In the case of the atmosphere using a mixed gas of nitrogen and hydrogen, the hydrogen concentration is preferably in the range from 0.1% to 10%, both inclusive, and more preferably in the range from 1% to 5%, both inclusive, in terms of securing minimum reduction power and safety of gas. To enhance the reactivity between the mixed phosphor materials, it is preferable that the materials are temporary fired in the air, for example, at a temperature between 400° C. and 1400° C. in advance.
(Fourth Process: Subsequent Process of the Fired Substance)
Lastly, the fired substance (phosphor) obtained by the firing process is subjected to a subsequent process, thereby obtaining a silicate phosphor. The subsequent process mainly includes a pulverizing step (which means a step of reducing the substance into a powder), a classifying step, a cleaning step and a drying step.
In the pulverizing step, the as-fired phosphor obtained by the firing (agglomeration of particles) is reduced into particles. To pulverize the fired substance, various techniques may be used. Examples of these techniques include pulverizing with a mortar, pulverizing with a ball mill, pulverizing utilizing a V-shaped mixer, pulverizing utilizing a cross rotary mixer, pulverizing with a jet mill and pulverizing with a crusher, a motor grinder, a vibrating cup mill, a disk mill, a rotor speed mill, a cutting mill and a hammer mill. As a method for pulverizing, dry pulverizing for pulverizing the fired substance without using any solvent or wet pulverizing for adding the fired substance to a solvent such as water or an organic solvent to pulverize the fired substance within the solvent may be used. As the organic solvent, ethanol or methanol may be used.
In the classifying step, the aggregation of phosphor particles obtained through the pulverizing is changed into an aggregation of particles having a given particle-size distribution. As the classification, various techniques may be used. Examples of these techniques include classification with a screen and classification utilizing sedimentation of phosphor particles in a solvent such as water or alcohol. In the classification with a screen, the use of a screen of about 50 to 1000 mesh can achieve a silicate phosphor having a particle size within the range (described in the first embodiment) suitable to application to a light-emitting semiconductor device. As a method for classification, dry classification using neither solvent nor wet classification for adding the pulverized substance to a solvent such as water or an organic solvent to classify the pulverized substance together with the solvent may be used. Two or more of these classifying techniques are used in some cases for the purpose of obtaining a sharp particle distribution.
In the cleaning step, a residual flux component contained in the fired substance after the firing and fine particles mixed in the product during the pulverizing or classification step are mainly removed. Various techniques may also be used as the cleaning step. Examples of these techniques include cleaning with acid, cleaning with alkali, cleaning with water such as distilled water or pure water, and cleaning with an organic solvent such as ethanol or methanol. The phosphor particles after the pulverizing or classification are cleaned by using a solvent appropriately selected according to the type or composition of the phosphor materials. The wet pulverizing step or the wet classifying step may be used such that the step also serves as the cleaning step. The cleaning step may be omitted depending on the type of the phosphor to be produced.
In the drying step, the aggregation of phosphor particles obtained through the pulverizing, classifying and cleaning steps is heated and a large or small amount of a solvent such as water or an organic solvent contained in the aggregation is evaporated and dried, thereby obtaining an aggregation of phosphor particles which is a final product or close to a final product. Various kinds of techniques may be used as the drying step. Examples of these techniques include drying with a thermostatic dryer or a vacuum dryer. If the thermostatic dryer is used, drying is performed at about 60 to 300° C. for about 30 minutes to 100 hours. The drying step as well as the cleaning step may be omitted for some types of a phosphor to be produced.
The pulverizing, classifying, cleaning and drying steps may be flexibly combined in any sequence and the number of times for performing each of the steps may also be determined flexibly according to the type and purpose of the phosphor.
Concrete Example of Method for Producing Silicate Phosphor
Hereinafter, a concrete example of a method for producing a silicate phosphor and effects of a flux will be described with reference to experimental data.
From the X-ray diffraction pattern of the primary fired substance, it is confirmed that a (Sr0.93Ba0.05Eu0.02)2SiO4 silicate phosphor having an orthorhombic structure is present in the primary fired substance fired at a primary firing temperature of 800° C. or more. It is also confirmed that each of the primary fired substances obtained by being fired at primary firing temperatures of 1000° C., 1200° C. and 1400° C., respectively, has an orthorhombic crystal structure, i.e., has substantially one kind of crystal structure.
From the X-ray diffraction pattern of the secondary fired substance, it is confirmed that every secondary fired substrate is a (Sr0.93Ba0.05Eu0.02)2SiO4 silicate phosphor having an orthorhombic structure, irrespective of the primary firing temperature. Specifically,
First Concrete Example of Method for Fabricating Light-Emitting Semiconductor Device
Now, a concrete example of a method for fabricating a light-emitting semiconductor device according to the present invention is described with reference to the drawings. As a first concrete example, a method for fabricating a white-light-emitting semiconductor device using a transfer technique and fabrication apparatus therefor are described.
First, a blue-light-emitting semiconductor chip 101 as a blue LED shown in
In a process step shown in
Next, in a process step shown in
Thereafter, the anode 102a of the Zener diode 102 is connected to an electrode terminal 104 provided on the substrate 103. In this embodiment, to establish this connection, the anode 102a is connected to the electrode terminal 104 using a gold wire 105. In this manner, the cathode 101b of the blue-light-emitting semiconductor chip 101 is electrically connected to the electrode terminal 104 of the substrate 103. The cathode 102b of the Zener diode 102 may be connected to the electrode terminal 104 provided on the substrate 103, or the anode 102a and cathode 102b of the Zener diode 102 may be connected to respective electrode terminals 104 provided on the substrate 103.
Then, in a process step shown in
In this way, the method for fabricating a white-light-emitting semiconductor device using the transfer technique includes: the process step of connecting the blue LED 101 as a blue-light-emitting device to the Zener diode 102 (substrate); and the process step of providing the phosphor particles 108 and the resin 106 such that the light emitted by the blue LED 101 passes therethrough.
More specifically, the method includes: the step of connecting, on a wafer 109 including a plurality of Zener diodes 102 as shown in
Such a fabrication method allows the fabrication of a white-light-emitting semiconductor device including a blue LED, a Zener diode (a substrate) to which the blue LED is electrically connected and a luminescent layer in which phosphor particles are dispersed in a resin and which is provided such that the light emitted by the blue LED passes through the luminescent layer.
In addition, it is also possible to fabricate a white-light-emitting semiconductor device including no Zener diode and including a blue LED and a luminescent layer in which phosphor particles are dispersed in a resin and which is provided such that the light emitted by the blue LED passes through the luminescent layer.
Examples of materials constituting the blue LED of this concrete example include a gallium nitride-based compound semiconductor, a zinc selenide semiconductor and a zinc oxide semiconductor. As a phosphor material, the phosphor used in the first embodiment may be used and, in particular, a silicate phosphor is preferably selected.
Second Concrete Example of Method for Fabricating Light-Emitting Semiconductor Device
Now, a method for fabricating a bulletlike light-emitting semiconductor device and fabrication apparatus are described as a second concrete example with reference to the drawings.
First, in a process step shown in
Thereafter, in a process step shown in
Then, in a process step shown in
Thereafter, in a process step shown in
Subsequently, the resin is cured, thereby obtaining a bulletlike white-light-emitting semiconductor device as shown in
In this case, it is sufficient for the frame 110 on which the blue LED 101 is placed to have a recessed shape in cross-section. Thus, the frame 110 includes: a mounting portion 112a (the bottom face of the recess in this case) for mounting the blue LED; a side 112b surrounding the mounting portion 112a; and terminals 112c and 113 such that a luminescent layer can be formed in a space (the recess 111) made by the mounting portion 112a and the side 112b. The shape of the recess 111 may be any one of a bottomless cylinder, a bottomless polygonal prism, a bottomless cone, a bottomless pyramid, a topless or bottomless truncated cone and a topless or bottomless truncated pyramid.
Thus, the side 112b is configured to reflect light emitted by the blue LED 101 placed on the mounting portion 112a (the bottom), so that it is possible to improve the external light extraction efficiency of the entire light-emitting semiconductor device.
It is preferable that the resin 115 in which the phosphor particles 116 are dispersed is supplied to the recess 111 to a level lower than the height of the side thereof. That is to say, the luminescent layer 119 is preferably lower than the upper edge of the recess 111. This is common among the cases where the shapes of the recess 111 are a cylinder, a polygonal prism, a cone, a pyramid, a truncated cone and truncated pyramid, respectively. In this manner, in the case where a plurality of white-light-emitting semiconductor devices are provided and lights emitted by the respective white-light-emitting semiconductor devices are to be utilized, it is possible to solve the problem of crosstalk that occurs between adjacent ones of the white-light-emitting semiconductor devices when blue light emitted by one excites phosphor particles included in a resin in the other. In particular, a device which emits white light by utilizing blue light from the blue-light-emitting semiconductor device and yellow light from a phosphor excited by the blue light has a structure with which the blue light is also emitted to the outside, so that such a problem of crosstalk is serious. However, if the luminescent layer 119 is lower than the height of the side 112b of the recess 111, such a problem of crosstalk can be eliminated.
As described above, the method for fabricating the light-emitting semiconductor device of the second concrete example is a fabrication method (or fabrication apparatus) including: a step of (means for) mounting a blue LED 101 on a mounting portion 112a; and a step of (means for) forming a luminescent layer 119 made of a mixture of phosphor particles 116 and a resin 115 such that light emitted by the blue LED passes through the luminescent layer 119.
Still more specifically, the fabrication method (or fabrication apparatus) includes: a step of (or means for) providing the blue-light-emitting diode on the mounting portion; a step of (or means for) providing a first resin including a phosphor in such a situation that light emitted by the blue-light-emitting diode passes through the resin; and a step of (or means for) providing a second resin including no phosphor in such a situation that light emitted by the blue-light-emitting diode passes through the resin. In this case, a resin which does not cure with heat is preferably selected as the first resin, while a resin which cures with heat is preferably selected as the second resin.
As a material constituting the blue LED, a nitride gallium-based compound semiconductor, a zinc selenide semiconductor and a zinc oxide semiconductor may be used. As a phosphor material, the materials used in the first embodiment may be used and, in particular, a silicate phosphor is preferably selected.
In this concrete example, the epoxy resin is used as the resin 115. Alternatively, any other resins such as a silicone resin may be used.
The anode and cathode of the blue LED are electrically connected to the respective terminals via the gold wires. However, the wires may be made of any material so long as electric connections are established. For example, aluminum wires may used.
Third Concrete Example of Method for Fabricating Light-Emitting Semiconductor Device
Now, a method for fabricating a side-view type white-light-emitting semiconductor device and fabrication apparatus are described as a third concrete example.
First, in a process step shown in
Thereafter, in a process step shown in
Then, in a process step shown in
Subsequently, the resin is cured, thereby obtaining a side-view type white-light-emitting semiconductor device as shown in
In this case, it is sufficient for the casing 120 on which the blue LED 101 is placed to have a recessed shape in cross-section. Thus, the casing 120 includes a base 120 for mounting the blue LED thereon, a side 121 surrounding the recess 128 on the base 120; and the externally connecting terminals 122 and 123 such that a luminescent layer can be formed in a space (the recess 128) made by the base 120 and the side 121. The shape of the recess 128 may be any one of a bottomless cylinder, a bottomless polygonal prism, a bottomless cone, a bottomless pyramid, a topless or bottomless truncated cone and a topless or bottomless truncated pyramid.
Thus, the side 121 is configured so as to serve as a reflecting plate for reflecting light emitted by the blue LED 101 placed on the base 120, so that it is possible to enhance the external light extraction efficiency of the entire light-emitting semiconductor device.
It is preferable that the resin 125 in which the phosphor particles 126 are dispersed is supplied to a level lower than the height of the side 121 (the side wall of the recess). That is to say, the luminescent layer 129 is preferably lower than the upper edge of the recess 128. This is common among the cases where the shapes of the recess 128 are a cylinder, a polygonal prism, a cone, a pyramid, a truncated cone and truncated pyramid, respectively. In this manner, in the case where a plurality of white-light-emitting semiconductor devices are provided and lights emitted by the respective light-emitting semiconductor devices are to be utilized, it is possible to solve the problem of crosstalk that occurs between one of the white-light-emitting semiconductor devices and an adjacent one of the white-light-emitting semiconductor devices when blue light emitted by the one excites phosphor particles included in a resin in the other. In particular, a device which emits white light by utilizing blue light from the blue-light-emitting semiconductor device and yellow light from a phosphor excited by the blue light has a structure with which the blue light is also emitted to the outside, so that such a problem of crosstalk is serious. However, if the luminescent layer 129 is lower than the height of the side 121, such a problem of crosstalk can be eliminated.
As described above, the method for fabricating the light-emitting semiconductor device of the third concrete example is a fabrication method including: a step of mounting a blue LED 101 (blue-light-emitting device) on a base 120; and a step of forming a luminescent layer 129 made of a mixture of phosphor particles 126 and a resin 125 such that light emitted by the blue LED passes through the luminescent layer.
More specifically, the fabrication method includes: a step of mounting the blue-light-emitting device on the base; a step of providing the luminescent layer such that light emitted by the blue-light-emitting device passes through the luminescent layer; and a step of providing a permeable resin including no phosphor such that the light emitted by the blue-light-emitting diode passes through the resin. In this case, a resin which does not cure with heat is preferably selected as the resin constituting the luminescent layer and a resin which cures with heat is preferably selected as the resin including no phosphor.
As a material constituting the blue LED, a nitride gallium-based compound semiconductor, a zinc selenide semiconductor and a zinc oxide semiconductor may be used. As a phosphor material, the materials used in the first embodiment may be used and, in particular, a silicate phosphor is preferably selected.
In this concrete example, the epoxy resin is used as the resin 125. Alternatively, any other resins such as a silicone resin may be used.
The anode and cathode of the blue LED are electrically connected to the respective terminals via gold wires. However, the wires may be made of any material so long as electric connections are established. For example, aluminum wires may be used.
In the processes for fabricating the light-emitting semiconductor devices according to the respective concrete examples, the phosphor particles are preferably dispersed as evenly as possible in the resin. In view of this, concrete examples for dispersing the phosphor particles evenly throughout the resin in the processes for fabricating a light-emitting semiconductor device will be described below.
First Concrete Example for Dispersing Phosphor Particles Evenly
As a first concrete example, a method for applying vibration during curing of a resin and an apparatus therefor are described.
In the same manner, in the step shown in
Second Concrete Example for Dispersing Phosphor Particles Evenly
As a second concrete example, a method and apparatus for turning over a mold while a resin is curing are described.
In this case, as the number of rotating the mold 107 increases, the phosphor particles 108 disperse more evenly in the resin 106. In addition, since about 90% of the whole of the resin cures for the first one hour, the mold 107, i.e., the resin 106, is preferably turned over within this first one hour.
In this case, as the number of rotating the mold 117 increases, the phosphor particles 116 disperse more evenly in the resin 115. In addition, since about 90% of the whole of the resin cures for the first one hour, the mold 117, i.e., the resin 115, is preferably turned over within this first one hour.
In the same manner, in the step shown in
Third Concrete Example for Dispersing Phosphor Particles Evenly
As a third concrete example, a method for performing, a plurality of times, a process of filling a recess or a mold with a resin and then curing the resin is described.
In this concrete example, in the step shown in
By thus pouring and curing the resin through the process repeated a plurality of times, the phosphor particles 108 disperse relatively evenly in the resin 106 without sedimenting in the bottom of the resin 106 in the luminescent layer 109 as shown in
In the same manner, in the step shown in
In this case, as the number of steps of pouring and curing the resin in the mold or recess increases, the phosphor particles disperse more evenly in the resin. However, since a larger number of the steps require a longer fabrication time, the number of the steps is preferably five or less, and most preferably about three.
Fourth Concrete Example for Dispersing Phosphor Particles Evenly
As a fourth concrete example, a method using a high-viscosity resin in forming a luminescent layer will be described.
In this concrete example, in a process for fabricating a light-emitting semiconductor device (e.g., the step shown in
By thus using the high-viscosity resin, the phosphor particles 108 disperse relatively evenly in the resin 106 without sedimenting in the bottom of the resin 106 in the luminescent layer 109 as shown in
In the same manner, in the step shown in
Fifth Concrete Example for Dispersing Phosphor Particles Evenly
As a fifth concrete example, a method using a resin which does not need heat for curing in forming a luminescent layer will be described.
In this concrete example, in a process for fabricating a light-emitting semiconductor device (e.g., the step shown in
As a result, it was found that the use of a resin which cures with heat causes the phosphor particles 108 to sediment to some extent because such a resin has its viscosity decreased in a certain period before curing, whereas the use of the ultraviolet-curing resin or two-liquid-curing resin which does not cure with heat allows the phosphor particles 108 to disperse relatively evenly in the resin 106.
In the same manner, in the step shown in
If the steps or means for dispersing the phosphor particles more evenly in the resin are provided as in the first through fifth concrete examples, the following effects are achieved. That is to say, as compared to the case where phosphor particles are unevenly distributed, if the phosphor particles are evenly dispersed, especially in a vertical direction, in the resin, it is possible to outwardly extract blue light (light whose emission spectrum has a peak between 450 nm and 560 nm) emitted by a blue LED, which is otherwise excessively confined in the unevenly distributed phosphor particles. As a result, appropriate white light can be obtained.
In addition, a problem that the fluorescence itself emitted by the phosphor particles is confined excessively in the unevenly distributed phosphor particles is eliminated. Therefore, it is possible to extract the fluorescence to the outside.
Moreover, as compared to the case where phosphor particles are unevenly dispersed in a resin, especially in the case where the phosphor sediments on the substrate 103 as shown in
The effects are obtained by using only one of the steps or means in the first through fifth concrete examples. However, further synergistic effects are created by using two or more of the steps or means.
Concrete Example Relating to Agitation for Luminescent Layer
In the phosphor paste 206 stored in the material tank 200 or the tank compartment 202, the phosphor particles 207 aggregate together with time and are likely to form a cluster of the phosphor particles 207. The formation of the cluster of the phosphor particles 207 causes the nozzle 203 to clog or the concentration of the phosphor particles 207 in the phosphor paste 206 to be ejected to vary, so that it is difficult to disperse the phosphor particles 207 evenly in the cavity CA in some cases. To avoid the difficulty, in the phosphor paste discharging apparatus of this example, the phosphor paste 207 stored in the material tank 200 or the tank compartment 202 is agitated, thereby suppressing the formation of the cluster of the phosphor particles 207. In the example shown in
A method for agitating the phosphor paste 207 in the material tank 200 or the tank compartment 202 is not limited to the method using the metal ball S as shown in
In addition, the phosphor paste discharging apparatus of this concrete example is provided with the dispersion nozzle 205 for controlling the flow rate of the phosphor paste 206. Accordingly, when the phosphor paste 206 passes through the dispersion nozzle 205, the cluster of the phosphor particles 207 in the phosphor paste 206 is separated into small pieces by a jet stream, thereby disassembling the cluster. If the neck diameter of the dispersion nozzle 205 is previously set to fit the nozzle diameter of the head 202, the cluster in the phosphor paste 206 created in the material tank 200 or in a supply path on the way to the material tank 200 is appropriately disassembled, thereby stabilizing the ejection from the nozzle 203. By suppressing the agglomeration of the phosphor in the head 202 via the dispersion nozzle 205, the nozzle 203 is prevented from clogging and, more over, the phosphor particles 207 are easily dispersed evenly in the cavity CA. The dispersion nozzle 205 is not necessarily provided and may be adaptively provided according to, for example, the viscosity of the silicate phosphor.
Electrification of Luminescent Layer
As described above, a large difference in specific gravity between a YAG-based phosphor and a base material is considered to be one cause of sedimentation of the phosphor. In addition, the fact that the YAG-based phosphor is always positively charged is considered another cause. That is to say, if a resin as the base material is positively charged, as is the YAG-based phosphor, the resin and the YAG-based phosphor repel each other in general, resulting in that the YAG-based phosphor sediments.
On the other hand, considering the fact that a silicate phosphor containing a component expressed by the chemical formula (Sr1-a1-b1-xBaa1Cab1Eux)2SiO4 as a main component does not sediment with respect to the same resin and the above-described relationship between electrification and sedimentation, the silicate phosphor particles are negatively charged, i.e., oppositely charged to the resin, so that the phosphor and the resin attract each other. As a result, it is concluded that the silicate phosphor particles disperse throughout the resin. Examples of such resins to be positively charged include an epoxy resin and a silicone resin.
In view of this, means for facilitating the dispersion of the YAG-based phosphor particles may be a method for coating the phosphor particles with an oxide to be negatively charged.
As a method for coating the surfaces of the phosphor particles with an oxide or a fluoride, a suspension of a phosphor paste and a suspension containing coating particles of a needed oxide or fluoride are mixed and agitated, and then subjected to suction filtration. Thereafter, the resultant substance is dried at 125° C. or higher and then is fired at 350° C. In order to enhance the adherability between the phosphor and the oxide or fluoride, a small amount of a resin, an organic silane or a liquid glass may be added.
As a method for applying a coating to the surfaces of the phosphor particles, a method utilizing the hydrolysis of an organic metal compound may be used. Then, a coating of SiO2, which is an oxide readily to be negatively charged, is applied to the surfaces of the phosphor particles. In forming an Al2O3 film, Al(OC2H5)3 which is aluminum alkoxide, is used for a phosphor so as to be mixed and agitated in an alcohol solution, thereby applying Al2O3 to the surface of the phosphor.
The present inventors found that by thus attaching or applying, as a coating, a member made of a material which is opposite to the resin in electrification polarity to the surfaces of the phosphor particles, resin particles surround the phosphor particles to which the member positively charged, i.e., oppositely charged to the resin, is attached or applied as a coating, resulting in suppressing agglomeration of the phosphor particles as well as preventing sedimentation of the phosphor particles. That is to say, the present inventors found that in either case of the YAG-based phosphor particles or the silicate phosphor particles, if members are selected such that at least the resin, in which the phosphor particles are dispersed, and the phosphor particles are charged oppositely to each other, such pronounced sedimentation of phosphor particles as observed in the known devices does not occur.
In this case, if the amount of an oxide of fluoride coating which is applied to the surfaces of the phosphor particles and is to be negatively charged is too small, only a small effect is achieved, whereas if the amount thereof is too large, the coating absorbs emission of light so that the luminance might decrease. Therefore, the present inventors have conducted various experiments to find that the amount of an oxide or fluoride coating which is applied to the surfaces of the phosphor particles and is to be negatively charged is preferably in the range from 0.05% to 2.0% of the phosphor particles in weight.
In this manner, as a further aspect of the present invention, provided is a structure in which an epoxy resin includes a YAG-based phosphor to which SiO2 is applied as a coating or attached. That is to say, the present invention provides a structure in which an epoxy resin includes a YAG-based phosphor to which an oxide or a fluoride to be negatively charged is attached or applied as a coating, and also provides a method for forming such a structure. More specifically, the present invention provides a structure in which a YAG-based phosphor to which an oxide or a fluoride to be negatively charged is attached or applied as a coating is included in an epoxy resin which is a resin causing the YAG-based phosphor to be negatively charged, and also provides a method for forming such a structure. Still more specifically, the present invention provides a structure in which light emitted by a blue LED passes through the epoxy resin and a method for forming such a structure, thereby making it possible to provide a white/whitish-light-emitting semiconductor device in which phosphor particles disperse evenly, as shown in
Example of Silicate Phosphor for Light-Emitting Semiconductor Device
Hereinafter, an implementation example of an inventive light-emitting semiconductor device will be described.
(Example of Procedure for Forming Silicate Phosphor)
First, silicate phosphor particles having a composition enough to emit yellow/yellowish light was formed. Powders of barium carbonate (BaCO3), strontium carbonate (SrCO3), europium oxide (Eu2O3) or silicon dioxide (SiO2) were used as materials for the phosphor. Calcium chloride (CaCl2) was used as a flux. Each of the materials has a purity of 99.9% or more and a particle size in the range from 10 nm to 5 μm, both inclusive. To eliminate errors in weighing caused by an adsorption gas, variation in weight of each of the materials before and after heating performed at about 900° C. in the air was previously examined and grasped.
After 9.9 g, 138.0 g, 2.6 g, 30.7 g and 1.7 g of powdery barium carbonate, strontium carbonate, europium oxide, silicon dioxide and calcium chloride, respectively, had been weighed with an electric balance, these powders were fully mixed with an automatic mortar, thereby obtaining a mixed phosphor material powder. Thereafter, an alumina boat was charged with the mixed phosphor material powder and then was placed in a given position within a tubular atmospheric furnace using an alumina as a core tube, and then firing was performed. The firing was performed at a heating temperature of 1400° C. in an ambient containing 5% hydrogen and 95% nitrogen for two hours.
After it was confirmed that the interior of the core tube was cooled to room temperature, the fired substance (silicate phosphor) was taken out and subjected to subsequent processes such as pulverizing, cleaning, classification and drying. In this manner, a silicate phosphor having an orthorhombic structure and emitting yellow/yellowish light was obtained.
Hereinafter, results of pre-evaluation performed on characteristics of the obtained silicate phosphor will be described. In this evaluation, the composition of the silicate phosphor, the excitation spectrum and emission spectrum of the silicate phosphor, the reflecting spectrum of blue excitation light, and the emission spectrum of a phosphor excited by blue light, were evaluated a sing a crystal component of the silicate phosphor particles obtained by an X-ray diffraction, a particle distribution and particle size of the silicate phosphor particles measured with a laser diffraction particle size analyzer, and an ICP spectroscopy.
Next, the composition of the silicate phosphor was evaluated using an ICP spectroscopy. As a result, it was found that the composition of the silicate phosphor is (Ca0.015Sr0.92Ba0.05Eu0.015)Si0.99Ox, which substantially coincides with the composition of an as-charged silicate phosphor.
Then, an excitation spectrum and an emission spectrum of the silicate phosphor were evaluated. A result of this evaluation is already shown with reference to
Various Characteristics of Silicate Phosphor
Hereinafter, the characteristics of the silicate phosphor formed by the above-described procedure will be described in detail.
Firstly, a relationship between the composition and the crystal structure of a silicate phosphor is described. The following descriptions are about a silicate phosphor obtained by setting the Eu concentration (which is defined as Eu/(Sr+Ba+Ca+Eu)) at a typical value of 2 at. % (i.e., Eu concentration=0.02) and by being fired at 1400° C. in a reducing atmosphere for two hours.
As has been described above, the silicate phosphor can be in at least three kinds of crystal structures such as an orthorhombic system, a monoclinic system and a hexagonal system depending on its composition. These kinds of crystal structures are described with reference to
These X-ray diffraction patterns show data measured at room temperature and atmospheric pressure.
The relationship between the compositions and the main crystal structures of silicate phosphors are shown in
With respect to the crystal structure, (Sr1-a1-xBaa1Eux)2SiO4 phosphors are worthy of special remark. A pure (Sr1-xEux)2SiO4 phosphor containing no Ba has a monoclinic structure at least in the Eu concentration range 0≤x≤0.1. However, if the (Sr1-a1-xBaa1Eux)2SiO4 phosphor contains about 1 at. % or more Ba in terms of substitution amount (=Ba/(Sr+Ba+Ca+Eu)), the phosphor has an orthorhombic structure at least in the Eu concentration range 0≤x≤0.3 (see
Next, a relationship between the composition and the emission characteristics of each silicate phosphor in this example is described. The following descriptions are also about silicate phosphors each obtained by setting the Eu concentration (which is defined as Eu/(Sr+Ba+Ca+Eu)) at a typical value of 2 at. % and by being fired at 1400° C. in a reducing atmosphere for two hours.
Comparison of the emission spectra under excitation by blue light, and excitation by ultraviolet radiation with a wavelength of 254 nm shows that the emission spectra are similar to each other, though the comparison was made for only part of the samples.
Although the excitation-light spectra of the respective silicate phosphors are not shown, it is confirmed through visual observations that the inventive (Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 silicate phosphor is a phosphor which can emit blue-green, green, yellow to orange light when excited by at least blue light with a main emission peak wavelength of 470 nm in the entire composition range in varying degrees and which has a main emission peak wavelength in the range from 505 nm to 598 nm.
Among the (Sr1-a3-b3-xBaa3Cab3Eux)2SiO4 silicate phosphors, a relatively high luminous efficacy is observed especially in those which contain a large proportion of Si.
As can be seen from the emission spectrum shown in
In summary, yellow/yellowish light is obtained from a silicate phosphor which is limited in composition range, i.e., the Ba substitution amount (a3) is in the range 0≤a3≤0.3 and the Ca substitution amount (b3) is in the range 0≤b3≤0.8. It is preferable that the Ba substitution amount (a3) is in the range 0<a3≤0.2 and the Ca substitution amount (b3) is in the range 0<b3≤0.7. As can be seen from
Next, a relationship among the Eu2+-luminescent-center concentration (=Eu/(Sr+Ba+Ca+Eu): equal to Eu concentration), the crystal structure and the emission characteristics of each silicate phosphor is described. The following descriptions are about silicate phosphors each having the composition of (Sr1-xEux)2SiO4 or (Sr0.95-xBa0.05Eux)2SiO4 and obtained by being fired at 1400° C. in a reducing atmosphere for two hours.
As can be seen from the experimental data, only orthorhombic silicate phosphors which are limited in composition as described above emit yellow/yellowish light observed when excited by ultraviolet radiation with a wavelength of 254 nm or the blue light.
From the foregoing experimental results, proper ranges of the respective elements of a silicate phosphor for achieving effects of the present invention are as follows.
Ba
Yellow light ranges between 550 nm and 600 nm, both inclusive, in wavelength. Therefore, from
Ca
Sr
Crystal Structure
Eu
Now, a Sr2SiO4:Eu2+ silicate phosphor and a (BaSr)2SiO4:Eu2+ phosphor recited as green phosphors in Japanese Laid-Open Publication No. 2001-143869 and herein mentioned as prior art are described
As has been described using the experimental data, so far as experiments done by the present inventors are concerned, the Sr2SiO4:Eu2+ silicate phosphor is a phosphor which can be in two crystal structures of an orthorhombic system and a monoclinic system, depending on an impurity such as Ba contained in trace amounts. At least as far as the amount of addition of Eu2+ luminescent centers practically used (=the number of Eu atoms/(the number of Sr atoms+the number of Eu atoms:x) is in the range 0.01<x<0.05 at room temperature and atmospheric pressure, an orthorhombic Sr2SiO4:Eu2+ (α′-Sr2SiO4:Eu2) is a yellow/yellowish phosphor emitting yellow/yellowish light at a main emission peak around the wavelength between 560 and 575 nm, and a monoclinic Sr2SiO4:Eu2+ (β′-Sr2SiO4:Eu2+) is a green phosphor emitting green light at a main emission peak around the wavelength between 535 and 545 nm (see
Experiments done by the present inventors also show that the main emission peak wavelength hardly varies if the Eu mole fraction (=Eu/(Sr+Eu) atomic percent) is in the practical range from 0.001 to 0.3, both inclusive (i.e., the range from 0.1 at. % to 30 at. %, both inclusive), especially in the range from 0.003 to 0.03, both inclusive. Therefore, the Sr2SiO4:Eu2+ green phosphor recited in Japanese Laid-Open Publication No. 2001-143869 can be considered a monoclinic Sr2SiO4:Eu2+ phosphor.
It is already publicly known that the crystal structure of a Sr2SiO4 compound can be in an orthorhombic system or a monoclinic system depending on a small amount of Ba contained (e.g., in G. PIEPER et al., Journal of the American Ceramic Society, Vol. 55, No. 12 (1972) pp. 619-622). It is also known that the crystal structure of a monoclinic Sr2SiO4 compound undergoes a reversible change into an orthorhombic system at about 383 K (see, for example, M. Catti et al., Acta Cryst., B39 (1983) pp. 674-679).
A compound in which the content percentage of Ba impurity atoms with respect to Sr atoms (Ba/(Sr+Ba) atomic percent, hereinafter referred to as Ba content) is about 1% or more, i.e., a compound having a Ba content higher than that of a (Sr0.9gBa0.01)2SiO4:Eu2+, has an orthorhombic structure and has a main emission peak wavelength varying from around 575 nm to around 505 nm as the Ba content increases (see
Another experiment done by the present inventors shows that the main emission peak wavelength hardly varies so long as the Eu concentration has a practical mole fraction in terms of luminous intensity, i.e., is in the range from 0.001 to 0.3, both inclusive, especially in the range from 0.003 to 0.03, both inclusive. Therefore, the (BaSr)2SiO4 Eu2+ green phosphor recited in Japanese Laid-Open Publication No. 2001-143869 can be considered a (Sr1-a3-xBaa3Eux)2SiO4 silicate phosphor (where the value x is in the range 0.001≤x≤0.3) having at least the composition range 0.3<a3≤0.98.
Lastly, comparison results in emission characteristics between a silicate phosphor ((Ca0.015Sr0.92Ba0.05Eu0.05)2SiO4 phosphor which has an orthorhombic structure and emits yellow/yellowish light and in which the Eu concentration is optimized, and a YAG-based phosphor ((Y0.7Gd0.28Ce0.02)3Al5O12), are described.
Luminance Characteristic Comparison Between YAG-Based Phosphor and Silicate Phosphor
First, the difference in luminance characteristic between a light-emitting semiconductor device using a YAG-based phosphor and a light-emitting semiconductor device using a silicate phosphor is described.
Then, weight percentages of the silicate phosphors are varied using samples F, G, H, I, J and K so as to measure effects on variations in luminance, chromaticity, total luminous flux and total radiant flux.
Addition of Thixotropy Improver
Now, described are effects obtained in the case where an ultra-fine-powdery silicon dioxide such as an ultra-fine-powdery silica (product name: “Aerosil” produced by Degussa Co., Ltd. (Germany)) is introduced, as a thixotropy improver (which is herein an agent having a function of improving a thixotropy index), in a silicate phosphor for a light-emitting semiconductor device.
Data shown in
The respective standard deviations of the luminance, chromaticity (value x), total luminous flux, total radiant flux for each of the samples are shown. The standard deviations of all the items for sample 3 are the smallest among the three samples, and therefore sample 3 is the most reliable. Although the values of the chromaticities differ to some degree among the samples and therefore the data therefore is used only as a reference, the luminance, luminous flux and radiant flux for sample 1 are high but the standard deviation of the chromaticity for sample 1 is the highest among the three samples, and thus it can be understood that the reliability of sample 1 is low.
From the foregoing, it is conjectured that as the amount of Aerosil to be added increases, the luminance, luminous flux and radiant flux increase as well as the reliability improves. This is because the thixotropy of the silicate phosphor paste is enhanced with Aerosil and therefore the viscosity of the phosphor paste is appropriately set. Specifically, while the silicate phosphor paste is introduced in the light-emitting semiconductor device, potting is smoothly performed with the viscosity kept appropriate, so that the silicate phosphor particles disperse relatively evenly in the phosphor paste. After the paste is placed in a cavity in the light-emitting device, the viscosity thereof shifts to higher levels than during the potting, thus keeping the state in which the silicate phosphor particles do not sediment but disperse relatively evenly in a base material. In this manner, the color unevenness as observed in YAG-based phosphors is suppressed, resulting in improvement in the luminance, luminous flux and reliability.
In this embodiment, a method for forming a thin luminescent layer is described. According to this embodiment, yellow/yellowish phosphor particles which are expressed by the chemical formula (Sr1-a1-b1-xBaa1Cab1Eux)2SiO4 where the values a1, b1 and x are in the ranges 0≤a1≤0.3, 0≤b1≤0.8 (more preferably 0≤b1≤0.6) and 0<x<1, respectively, and which emit light having an emission peak in the wavelength range from 550 nm to 600 nm, both inclusive, are densely distributed near a light-emitting diode, so that a luminescent layer is made thin, i.e., the thickness through which light passes is reduced, thereby reducing attenuation of light. For example, this embodiment is for a method for fabricating a light-emitting semiconductor device in which a luminescent layer has a substantial thickness in the range from 50 μm to 1000 μm, both inclusive, where a light extraction surface of a blue-light-emitting device is located.
Hereinafter, examples of the fabrication method will be described.
First Exemplary Fabrication Method
First, in a process step shown in
Next, in a process step shown in
Then, in a process step shown in
In this manner, it is possible to fabricate a white-light-emitting semiconductor device in which the phosphor particles 311 are densely distributed in a portion of the base material 310 located at least over the main light extracting surface of the light-emitting diode 302 and which exhibits small color unevenness. If such a light-emitting semiconductor device is installed in any of the light-emitting systems shown in
Second Exemplary Fabrication Method
First, in a process step shown in
Next, in a process step shown in
Then, in a process step shown in
In this manner, it is possible to fabricate a light-emitting semiconductor device in which the phosphor particles 411 are densely distributed in a portion of the base material 410 located at least over the main light extracting surface of the light-emitting diode 402 and which exhibits small color unevenness. If such a light-emitting semiconductor device is installed in any of the light-emitting systems shown in
Third Exemplary Fabrication Method
First, in a process step shown in
Next, in a process step shown in
Then, in a process step shown in
Then, in a process step shown in
In this manner, it is possible to fabricate a white-light-emitting semiconductor device in which the phosphor particles 511 are densely distributed in a portion of the base material 512 located at least over the main light extracting surface of the light-emitting diode 502 and which exhibits small color unevenness. If such a light-emitting semiconductor device is installed in any of the light-emitting systems shown in
(Fourth Exemplary Fabrication Method)
The difference in specific gravity between the phosphor and a base material is considered a cause of sedimentation of a YAG-based phosphor. The fact that the YAG-based phosphor is positively charged is also considered another cause of the sedimentation. Specifically, if a resin as the base material is positively charged, as is the YAG-based phosphor, the resin and the YAG-based phosphor repel each other in general, so that the YAG-based phosphor sediments.
On the other hand, considering the fact that silicate phosphor particles containing a compound expressed by (Sr1-a1-b1-xBaa1Cab1Eux)2SiO4 as a main component does not sediment in the same resin, and considering the relationship between the electrification and the sedimentation, the attracting relationship between the positively charged resin and the negatively charged silicate phosphor particles presumably contributes to substantially even distribution of the silicate phosphor particles in the resin. Examples of such resins to be positively charged include an epoxy resin and a silicone resin.
In view of this, means for sedimenting the silicate phosphor may be a method for coating the phosphor particles with, for example, an oxide to be positively charged.
Examples of the method for coating the surface of the phosphor with an oxide or a fluoride include the following methods. First, suspensions including phosphor particles and coating particles of a needed oxide or fluoride are mixed and agitated, and then subjected to suction filtration. Thereafter, the substance remaining after the filtration is dried at 125° C. or higher and then is fired at 350° C. In order to improve the adherability between the phosphor particles and the oxide or fluoride, a small amount of a resin, an organic silane or a liquid glass may be added.
To apply the coating, a method utilizing the hydrolysis of an organic metal compound may also be used. For example, if an Al2O3 film is to be formed, Al(OC2H5)3 which is aluminum alkoxide, is used for a phosphor and is mixed and agitated in an alcohol solution, thereby applying Al2O3 to the surface of the phosphor.
If the amount of positively charged oxide or fluoride coating which is applied to the surfaces of the phosphor particles is too small, only a small effect is achieved, whereas if the amount thereof is too large, the coating absorbs light emitted so that the luminance decreases and therefore such a large amount of the coating is also unfavorable. As a result of experiments, it is found that the amount is preferably in the range from 0.05% to 2.0% of the phosphor particles in weight.
In this manner, it is possible to fabricate a white-light-emitting semiconductor device in which phosphor particles are densely distributed in a portion of a base material located at least over a main light extracting surface of a light-emitting diode and which exhibits small color unevenness. If such a light-emitting semiconductor device is installed in any of the light-emitting systems shown in
According to the fabrication method of the third embodiment, it is possible to obtain a light-emitting semiconductor device in which a luminescent layer has a substantial thickness in the range from 50 μm to 1000 μm, both inclusive, where a light extraction surface of a blue-light-emitting device is located.
In the foregoing embodiments, a single blue LED is provided as a blue-light-emitting device in a light-emitting semiconductor device. However, the inventive light-emitting semiconductor device is not limited to these embodiments.
With this structure, it is possible to improve the luminous intensity of the white-light-emitting semiconductor device, or adjust the luminous intensity depending on the number of the mounted blue LEDs 601.
In the embodiment of the light-emitting system, the example in which a large number of light-emitting semiconductor devices each including one blue LED and one luminescent layer is described. However, the inventive light-emitting system is not limited to the embodiment.
In the structure shown in
With respect to the inventive light-emitting semiconductor device, various kinds of displaying systems (e.g., LED information display terminals, LED traffic lights, LED stoplights of vehicles, and LED directional lights) and various kinds of lighting systems (e.g., LED interior/exterior lights, courtesy LED lights, LED emergency lights, and LED surface emitting sources) are defined broadly as light-emitting systems. In particular, the inventive light-emitting semiconductor device is suitable for systems utilizing white light.
Kamei, Hidenori, Ikeda, Tadaaki, Sakanoue, Kei, Oshio, Shozo, Iwama, Katsuaki, Maeda, Toshihide, Kitahara, Hiromi, Hanada, Yasuyuki
Patent | Priority | Assignee | Title |
Patent | Priority | Assignee | Title |
4481422, | Jun 12 1969 | The United States of America as represented by the Secretary of the Army | Intrusion detecting camouflage fluorescent coating |
5045753, | Mar 28 1989 | Sharp Kabushiki Kaisha | Matrix display apparatus with repair wires |
5777433, | Jul 11 1996 | Lumileds LLC | High refractive index package material and a light emitting device encapsulated with such material |
5998925, | Jul 29 1996 | Nichia Corporation | Light emitting device having a nitride compound semiconductor and a phosphor containing a garnet fluorescent material |
6066861, | May 20 1998 | Osram GmbH | Wavelength-converting casting composition and its use |
6177030, | Apr 23 1998 | Konica Corporation | Stimulable phosphor and radiation image conversion panel by use thereof |
6207077, | Oct 13 1998 | OZEWAVE AUSTRALIA PTY LTD , A CORPORATION OF AUSTRALIA ACN 090 992 831 | Luminescent gel coats and moldable resins |
6245259, | Sep 20 1996 | Osram GmbH | Wavelength-converting casting composition and light-emitting semiconductor component |
6294800, | Feb 06 1998 | General Electric Company | Phosphors for white light generation from UV emitting diodes |
6429583, | Nov 30 1998 | CURRENT LIGHTING SOLUTIONS, LLC F K A GE LIGHTING SOLUTIONS, LLC | LIGHT EMITTING DEVICE WITH BA2MGSI2O7:EU2+, BA2SIO4:EU2+, OR (SRXCAY BA1-X-Y)(A1ZGA1-Z)2SR:EU2+PHOSPHORS |
6458512, | Oct 13 1998 | 3M Innovative Properties Company | Oxynitride encapsulated electroluminescent phosphor particles |
6547617, | Jul 08 1998 | MATSUSHITA ELECTRIC INDUSTRIAL CO , LTD | Plasma display panel manufacturing method for manufacturing a plasma display panel with superior picture quality, a manufacturing apparatus and a phosphor ink |
6614170, | Dec 29 2000 | Arima Optoelectronics Corporation | Light emitting diode with light conversion using scattering optical media |
6621211, | May 15 2000 | CURRENT LIGHTING SOLUTIONS, LLC F K A GE LIGHTING SOLUTIONS, LLC | White light emitting phosphor blends for LED devices |
6635363, | Aug 21 2000 | CURRENT LIGHTING SOLUTIONS, LLC F K A GE LIGHTING SOLUTIONS, LLC | Phosphor coating with self-adjusting distance from LED chip |
6680569, | Feb 18 1999 | Lumileds LLC | Red-deficiency compensating phosphor light emitting device |
7023019, | Sep 03 2001 | Panasonic Corporation | Light-emitting semiconductor device, light-emitting system and method for fabricating light-emitting semiconductor device |
7132786, | Jul 23 1999 | OSRAM Opto Semiconductors GmbH; OSRAM OLED GmbH | Luminescent array, wavelength-converting sealing material and light source |
7332746, | Sep 02 1999 | Toyoda Gosei, Co., Ltd. | Light-emitting apparatus |
20020185965, | |||
20030218228, | |||
20040094757, | |||
20040104391, | |||
20060124942, | |||
EP550937, | |||
EP1095998, | |||
EP2006924, | |||
JP10163535, | |||
JP1077468, | |||
JP11035372, | |||
JP11145519, | |||
JP11233831, | |||
JP11251640, | |||
JP1131845, | |||
JP1187778, | |||
JP2000017257, | |||
JP2000031531, | |||
JP2000031547, | |||
JP2000087030, | |||
JP2000147766, | |||
JP2000150966, | |||
JP2000160155, | |||
JP200017257, | |||
JP2000208822, | |||
JP2000228544, | |||
JP2000244021, | |||
JP200031547, | |||
JP2000345152, | |||
JP2000349346, | |||
JP200087030, | |||
JP2001015817, | |||
JP2001026416, | |||
JP2001077433, | |||
JP2001135861, | |||
JP2001143869, | |||
JP2001144331, | |||
JP2001148516, | |||
JP200115817, | |||
JP2001177158, | |||
JP2001196639, | |||
JP2001228809, | |||
JP2004505470, | |||
JP2007329511, | |||
JP2927279, | |||
JP3749243, | |||
JP3756930, | |||
JP5230451, | |||
JP5287082, | |||
JP5334999, | |||
JP60177028, | |||
JP9017350, | |||
RE32498, | Mar 27 1981 | Hitachi, Ltd. | Method of manufacturing fluorescent screens of cathode ray tubes |
WO19546, | |||
WO33389, | |||
WO108453, | |||
WO160943, | |||
WO2054502, | |||
WO211214, | |||
WO9805078, | |||
WO9812757, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Jul 05 2016 | Panasonic Corporation | (assignment on the face of the patent) | / | |||
May 21 2020 | Panasonic Corporation | PANASONIC SEMICONDUCTOR SOLUTIONS CO , LTD | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 052755 | /0917 |
Date | Maintenance Fee Events |
Mar 10 2021 | M1553: Payment of Maintenance Fee, 12th Year, Large Entity. |
Date | Maintenance Schedule |
Jun 25 2022 | 4 years fee payment window open |
Dec 25 2022 | 6 months grace period start (w surcharge) |
Jun 25 2023 | patent expiry (for year 4) |
Jun 25 2025 | 2 years to revive unintentionally abandoned end. (for year 4) |
Jun 25 2026 | 8 years fee payment window open |
Dec 25 2026 | 6 months grace period start (w surcharge) |
Jun 25 2027 | patent expiry (for year 8) |
Jun 25 2029 | 2 years to revive unintentionally abandoned end. (for year 8) |
Jun 25 2030 | 12 years fee payment window open |
Dec 25 2030 | 6 months grace period start (w surcharge) |
Jun 25 2031 | patent expiry (for year 12) |
Jun 25 2033 | 2 years to revive unintentionally abandoned end. (for year 12) |