Patent Grant
8310145
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-201336, filed on Sep. 8, 2010; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a light emitting device.
Recently, attention focuses on a so-called white-color Light Emitting Device (LED) in which a yellow phosphor such as YAG:Ce is combined with a blue LED to emit white-color light by single chip. Conventionally, the LED emits red, green, or blue light in monochromatic form, and it is necessary that plural LEDs emitting monochrome wavelengths are driven in order to emit the white-color light or intermediate-color light. However, currently, the combination of the light emitting diode and the phosphor realizes the white-color light with a simple structure.
However, in the white-color light emitting diode in which the YAG:Ce phosphor is combined with the blue light emitting diode, pale light emission is generated because of a lack of a red component, and a color rendering property is biased. Therefore, there is discussed a white-color light emitting diode in which the red component lacking in YAG:Ce is compensated by another red phosphor having a peak wavelength of about 640 nm to about 660 nm.
A light emitting device according to one embodiment includes a light emitting element that emits light having a wavelength of 380 nm to 470 nm; a first red phosphor that is disposed on the light emitting element, the first red phosphor having a composition expressed by the following equation (1); a second red phosphor that is disposed on the light emitting element, the second red phosphor having a composition expressed by the following equation (2); and a green phosphor that is disposed on the light emitting element, the green phosphor having a composition expressed by the following equation (3).
(Ca1−x1Eux1)a1AlSib1Oc1Nd1:Eu (1)
(In the equation (1), x1, a1, b1, and c1 satisfy the following relationship. 0<x1<0.03, 0.90<a1<1.1, 0.90<b1<1.1, 0.20<c1<0.45, 2.40<<d1≦3.00)
(Sr1−x2Eux2)a2Sib2AlOc2Nd2 (2)
(In the equation (2), x2, a2, b2, c2, and d2 satisfy the following relationship. 0<x2≦1, 0.60<a2<0.95, 2.0<b2<3.9, 0.04≦c2≦0.6, 4<d2<5.7)
(Sr1−xEux)3−ySi13−zAl3+zO2+uN21−w (3)
(In the equation (3), x, y, z, u, and w satisfy the following relationship. 0<x≦1, −0.1≦y≦0.15, −1≦z≦1, −1<u−w≦1.5)
Embodiments will be described below with reference to the drawings.
In the following description, a color rendering property is based on an evaluation method defined by JISZ8726.
For example, the LED chip 12 is connected to wiring (not illustrated) through a gold wire 14. A driving current is supplied to the LED chip 12 from the outside through the wiring, whereby the LED chip 12 emits the blue light for excitation.
The LED chip 12 is sealed in the recess of the board 10 by a transparent resin layer 16. A hemispherical transparent resin layer 18 is provided on the LED chip 12 such that the transparent resin layer 16 is covered with the transparent resin 18.
A red fluorescent layer 20 is formed or disposed on the LED chip 12. And the red fluorescent layer 20 is disposed on the transparent resin layer 18. The red fluorescent layer absorbs the blue light emitted from the LED chip 12 and converts the blue light into red light. In the red fluorescent layer 20, the first red phosphor having the composition expressed by the equation (1) and the second red phosphor having the composition expressed by the equation (2) are dispersed in a transparent resin while mixed together.
(Ca1−x1Eux1)a1AlSib1Oc1Nd1:Eu (1)
(In the equation (1), x1, a1, b1, and c1 satisfy the following relationship. 0<x1<0.03, 0.90<a1<1.1, 0.90<b1<1.1, 0.20<c1<0.45, 2.40<d1≦3.00)
(Sr1−x2Eux2)a2Sib2AlOc2Nd2 (2)
(In the equation (2), x2, a2, b2, c2, and d2 satisfy the following relationship. 0<x2≦1, 0.60<a2<0.95, 2.0<b2<3.9, 0.04≦c2≦0.6, 4<d2<5.7)
The first red phosphor is a so called CASN phosphor. When excited by the blue light having the wavelength of 380 nm to 470 nm, the first red phosphor emits the red light having a peak at the wavelength of 640 nm to 660 nm.
The second red phosphor is a so called sialon phosphor. When excited by the blue light having the wavelength of 380 nm to 470 nm, the second red phosphor emits the red light having a peak at the wavelength of 590 nm to 630 nm.
From the viewpoint of realizing the higher color rendering property, in the second red phosphor, in the equation (2), desirably x2, a2, b2, c2, and d2 satisfy the relationship of 0.01<x2≦0.10, 0.62≦a2≦0.70, 2.1≦b2≦2.5, 0.4≦c2≦0.5, 4.1≦d2≦4.5.
A green fluorescent layer 22 is provided such that the red fluorescent layer 20 is covered therewith. A green fluorescent layer 22 is formed or disposed on the red fluorescent layer 20. In the green fluorescent layer 22, a green phosphor is dispersed in a transparent resin, and the green phosphor absorbs the blue light emitted from the LED chip 12 and converts the blue light into green light. In the green fluorescent layer 22, the green phosphor having the composition expressed by the equation (3) is dispersed in the transparent resin.
(Sr1−xEux)3−ySi13−zAl3+zO2+uN21−w (3)
(In the equation (3), x, y, z, u, and w satisfy the following relationship. 0<x≦1, −0.1≦y≦0.15, −1≦z≦1, 1<u−w≦1.5)
The green phosphor is a sialon phosphor. When excited by the blue light having the wavelength of 380 nm to 470 nm, the green phosphor emits the green light having a peak at the wavelength of 510 nm to 530 nm, for example.
A transparent resin layer 24 is provided such that the green fluorescent layer 22 is covered therewith. An outer surface of the transparent resin layer 24 is in contact with an atmosphere (air).
The transparent resin layer 24 has a function of suppressing total reflection of the blue light emitted from the LED chip 12, the red light from the red fluorescent layer 20, and the green light from the green fluorescent layer 22 at the outer surface that becomes an interface with the atmosphere.
A stacked film having a four-layer structure including the transparent resin layer 18, the red fluorescent layer 20, the green fluorescent layer 22, and the transparent resin layer 24 has a hemispherical shape.
According to the first embodiment, because particularly the two kinds of phosphors, that is, the so-called CASN phosphor and sialon phosphor are used as the red fluorescent, the color rendering property is realized as high as an average color rendering index Ra of 97 for a white color (4200 K) and an warm-white color (2800 K). Particularly the high color rendering property is realized for special color rendering indexes R9 and R15.
A transparent resin layer that suppresses re-absorption of the green light by the fluorescent layer 20 may further be provided between the red fluorescent layer 20 and the green fluorescent layer 22.
A yellow fluorescent layer in which a yellow phosphor is dispersed in a resin may further be provided between the red fluorescent layer 20 and the green fluorescent layer 22 in order to realize the higher color rendering property.
As illustrated in
A light emitting device according to a second embodiment differs from the light emitting device of the first embodiment only in that the first red phosphor as the first red fluorescent layer is disposed on the light emitting element, the second red phosphor as the second red fluorescent layer on the first red fluorescent layer is disposed on the light emitting element, and the green phosphor as the green fluorescent layer on the second red fluorescent layer is disposed on the light emitting element. Therefore, the descriptions of the contents overlapped with those of the first embodiment are omitted.
(Ca1−x1Eux1)a1AlSib1Oc1Nd1:Eu (1)
(In the equation (1), x1, a1, b1, and c1 satisfy the following relationship. 0<x1<0.03, 0.90<a1<1.1, 0.90<b1<1.1, 0.20<c1<0.45, 2.40<d1≦3.00)
(Sr1−x2Eux2)a2Sib2AlOc2Nd2 (2)
(In the equation (2), x2, a2, b2, c2, and d2 satisfy the following relationship. 0<x2≦1, 0.60<a2<0.95, 2.0<b2<3.9, 0.04≦c2≦0.6, 4<d2<5.7)
According to the second embodiment, the red fluorescent layer is divided into two layers, which the first red phosphor to be prevented from absorbing the red light emitted from the second red phosphor. Accordingly, higher luminous efficiency can be realized in addition to the effect of the first embodiment.
A light emitting device according to a third embodiment differs from the light emitting device of the first embodiment only in that a transparent resin layer is further provided between the red fluorescent layer and the green fluorescent layer. Therefore, the descriptions of the contents overlapped with those of the first embodiment are omitted.
Alight emitting device according to a fourth embodiment differs from the light emitting device of the second embodiment only in that a transparent resin layer is further provided between the second red fluorescent layer and the green fluorescent layer. Therefore, the descriptions of the contents overlapped with those of the second embodiment are omitted.
A light emitting device according to a fifth embodiment differs from the light emitting device of the third embodiment only in that the light emitting element is an LED that emits near-ultraviolet light having the wavelength of 380 nm to 420 nm and a blue fluorescent layer is provided instead of the transparent resin layer with which the green fluorescent layer is covered. Therefore, the descriptions of the contents overlapped with those of the third embodiment are omitted.
In the blue fluorescent layer 28, the blue phosphor is dispersed in the transparent resin, and the blue phosphor absorbs the ultraviolet light emitted from the LED chip 12 and converts the ultraviolet light into the blue light. For example, an apatite phosphor or BAM:Eu can be used as the blue phosphor.
According to the fifth embodiment, the high color rendering property can be realized similar to the first to fourth embodiments.
A light emitting device according to a sixth embodiment differs from the light emitting device of the fourth embodiment only in that the light emitting element is the LED that emits the near-ultraviolet light having the wavelength of 380 nm to 420 nm and the blue fluorescent layer is provided instead of the transparent resin layer with which the green fluorescent layer is covered. Therefore, the descriptions of the contents overlapped with those of the fourth embodiment are omitted.
In the blue fluorescent layer 28, the blue phosphor is dispersed in the transparent resin, and the blue phosphor absorbs the ultraviolet light emitted from the LED chip 12 and converts the ultraviolet light into the blue light. For example, an apatite phosphor or BAM:Eu can be used as the blue phosphor.
According to the sixth embodiment, the high color rendering property can be realized similar to the first to fifth embodiments.
A light emitting device according to a seventh embodiment differs from the light emitting device of the fourth embodiment only in that the fluorescent layers and the transparent resin layer have not the hemispherical shape but a flat-plate shape. Therefore, the descriptions of the contents overlapped with those of the fourth embodiment are omitted.
According to the seventh embodiment, the high color rendering property can be realized similar to the first to sixth embodiments. Because the fluorescent resin application layer and the transparent resin layer are formed into the flat-plate shape, advantageously the light emitting device of the seventh embodiment is relatively easily produced.
A light emitting device according to an eighth embodiment differs from the light emitting device of the fifth embodiment only in that the fluorescent layers and the transparent resin layer have not the hemispherical shape but the flat-plate shape. Therefore, the descriptions of the contents overlapped with those of the fifth embodiment are omitted.
According to the eighth embodiment, the high color rendering property can be realized similar to the first to seventh embodiments. Because the fluorescent resin application layer and the transparent resin layer are formed into the flat-plate shape, advantageously the light emitting device of the eighth embodiment is relatively easily produced.
A light emitting device according to a ninth embodiment differs from the light emitting device of the sixth embodiment only in that the fluorescent layers and the transparent resin layer have not the hemispherical shape but the flat-plate shape. Therefore, the descriptions of the contents overlapped with those of the sixth embodiment are omitted.
According to the ninth embodiment, the high color rendering property can be realized similar to the first to eighth embodiments. Because the fluorescent resin application layer and the transparent resin layer are formed into the flat-plate shape, advantageously the light emitting device of the ninth embodiment is relatively easily produced.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the light emitting device described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the devices and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
For example, any binder resin that constitutes a base material of a sealing resin can be used as long as the binder resin transmits the light in a neighborhood of the peak wavelength of the light emitting element (excitation element) and a wavelength region longer than the neighborhood of the peak wavelength. Generally, examples of the binder resin include a silicone resin, an epoxy resin, a polydimethylcyclohexane derivative having an epoxy group, an oxetane resin, an acrylic resin, a cycloolefin resin, a urea resin, a fluorine resin, and a polyimide resin.
The light emitting device of the fourth embodiment illustrated in
When the obtained light emitting device of Example 1 was driven at 20 mA, the color rendering property was evaluated with respect to the average color rendering index Ra and the special color rendering indexes R9 and R15 based on the evaluation method of JISZ8726. The luminous efficiency of the light emitting device was also evaluated. The luminous efficiency was evaluated using an integrating sphere. TABLE 4 illustrates the result. In the evaluation of the peak wavelength, the single phosphor was irradiated with the excitation light of the blue LED to measure the wavelength of the emitted light.
TABLE 1 illustrates values of x, y, z, u, and w in the equation (3) that is of the composition of the sialon green phosphor. TABLE 2 illustrates values of x2, a2, b2, c2, and d2 in the equation (2) that is of the composition of the sialon red phosphor. TABLE 3 illustrates values of x1, a1, b1, c1, and d1 in the equation (1) that is of the composition of the CASN red phosphor.
The light emitting device was produced and evaluated similarly to Example 1 except that the sialon green phosphor illustrated in the field of Example 2 of TABLE 1 was applied to the green phosphor, the CASN red phosphor illustrated in the field of Example 2 of TABLE 3 was applied to the first red phosphor, and the sialon red phosphor illustrated in the field of Example 1 of TABLE 2 was applied to the second red phosphor. TABLE 4 illustrates the result.
The light emitting device of the first embodiment illustrated in
The light emitting device of the second embodiment illustrated in
The light emitting device of the third embodiment illustrated in
The light emitting device of the fifth embodiment illustrated in
The light emitting device of the seventh embodiment illustrated in
The light emitting device of the seventh embodiment illustrated in
The light emitting device of the fifth embodiment illustrated in
The light emitting device of the sixth embodiment illustrated in
The light emitting device of the fifth embodiment illustrated in
The light emitting device of the sixth embodiment illustrated in
The light emitting device of the ninth embodiment illustrated in
The light emitting device of the eighth embodiment illustrated in
The light emitting device of the ninth embodiment illustrated in
The light emitting device of the eighth embodiment illustrated in
The light emitting device similar to that of the third embodiment illustrated in
The light emitting device similar to that of the first embodiment illustrated in
The light emitting device similar to that of the third embodiment illustrated in
The sialon green phosphor illustrated in the field of Comparative example 4 of TABLE 1 was applied to the green phosphor, and the sialon red phosphor illustrated in the field of Comparative example 4 of TABLE 3 was applied to the red phosphor. The green phosphor has the composition out of the equation (3), and the red phosphor has the composition out of the equation (2). Both the green phosphor and the red phosphor have the low luminous efficiency that is not enough to produce the light emitting device.
The sialon green phosphor illustrated in the field of Comparative example 5 of TABLE 1 was applied to the green phosphor, and the sialon red phosphor illustrated in the field of Comparative example 5 of TABLE 3 was applied to the red phosphor. The green phosphor has the composition out of the equation (3), and the red phosphor has the composition out of the equation (2). Both the green phosphor and the red phosphor have the low luminous efficiency that is not enough to produce the light emitting device.
The silicate green phosphor illustrated in the field of Comparative example 6 of TABLE 1 was applied to the green phosphor, and the nitride red phosphor illustrated in the field of Comparative example 5 of TABLE 3 was applied to the red phosphor. Both the green phosphor and the red phosphor have the low luminous efficiency that is not enough to produce the light emitting device.
The light emitting device similar to that of the third embodiment illustrated in
The light emitting device similar to that of the third embodiment illustrated in
The light emitting device similar to that of the fifth embodiment illustrated in
The light emitting device similar to that of the fifth embodiment illustrated in
In the light emitting devices of Examples 1 to 16, the high average color rendering index Ra and special color rendering index R9 and R15 were obtained compared with the light emitting devices of Comparative examples 1 to 9. In Examples 1 to 16, the light emitting device having the structure in which the application structure suppresses the re-absorption between the phosphors had the luminous efficiency (luminous flux efficiency) higher than that of the light emitting device having no structure which the application structure suppresses the re-absorption between the phosphors.
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