Light emitting device
View Patent ↗A light emitting device according to one embodiment includes a light emitting element that emits light having a wavelength of 250 nm to 500 nm; plural red fluorescent layers that are formed above the light emitting element to include a red fluorescent material, the red fluorescent layers being disposed at predetermined intervals; and plural green fluorescent layers that are formed above the light emitting element to include a green fluorescent material, a distance between the light emitting element and the green fluorescent layers being larger than a distance between the light emitting element and the red fluorescent layers.
1. A light emitting device comprising:
a light emitting element emitting light having wavelength of 250 nm to 500 nm;
red fluorescent layers formed above the light emitting element, each of the red fluorescent layers including a red fluorescent material, the red fluorescent layers being disposed at predetermined intervals;
green fluorescent layers formed above the light emitting element, each of the green fluorescent layers including a green fluorescent material, a distance between the light emitting element and the green fluorescent lavers being larger than a distance between the light emitting element and the red fluorescent layers; and
a medium layer formed on the light emitting element, the medium layer being transparent, the medium layer including projections and recesses on a surface thereof, wherein
the red fluorescent layers are formed in the recesses, and
the green fluorescent layers are formed on the projections.
2. The device according to claim 1 , wherein
a cross-section of the medium layer above an upper surfaces of the red fluorescent layers has a shape in which trapezoids are adjacent to each other with a gap “b”, a side of the light emitting element is set to a lower base, “a” is a length of the lower base, “c” is a height, and “θ” and “φ” are angles in end portions of the lower base, and
equations (1) and (2) are satisfied when n 2 is a refractive index of the medium layer while n 1 is a refractive index of a substance being in contact with two sides of the trapezoidal shape;
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(where α=c/(a+b)).
3. The device according to claim 2 wherein equation (3) is satisfied when both the angles θ and φ are 90 degrees and n 1 =1 and n 2 =n.
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a
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b
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2
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4. A light emitting device comprising:
a light emitting element emitting light having wavelength of 250 nm to 500 nm;
red fluorescent layers formed above the light emitting element, each of the red fluorescent layers including a red fluorescent material, the red fluorescent layers being disposed at predetermined intervals; and
green fluorescent layers formed above the light emitting element, each of the green fluorescent layers including a green fluorescent material, a distance between the light emitting element and the green fluorescent layers being larger than a distance between the light emitting element and the red fluorescent layers,
wherein the red fluorescent material has a composition expressed by equation (4):
(M l−xl Eu x1 ) a Si b AlO c N d (4)
(In the equation (4), M is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (Aluminum), rare-earth elements, and IVB group elements. x1, a, b, c, and d satisfy the following relationship:
0<x1≦1,
0.60<a<0.95,
2.0<b<3.9,
0.04≦c≦0.6,
4<d<5.7).
5. The device according to claim 1 ,
wherein the green fluorescent material has a composition expressed by equation (5):
(M′ 1−x2 EU x2 ) 3−y Si 13−z Al 3+z O 2+u N 21−w (5)
(In the equation (5), M′ is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (Aluminum), rare-earth elements, and IVB group elements. x2, y, z, u, and w satisfy the following relationship:
0<x2≦1,
−0.1≦y≦0.15,
−1≦z≦1,
−1 21 u−w ≦1.5,
0≦w≦21).
6. The device according to claim 4 , wherein the green fluorescent material has a composition expressed by the equation (5):
(M′ 1−x2 EU x2 ) 3−y Si 13−z Al 3+z O 2+u N 21−w (5)
(In the equation (5), M′ is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al, rare-earth elements, and IVB group elements. x2, y, z, u, and w satisfy the following relationship:
0<x2≦1,
−0.1≦y≦0.15,
−1≦z≦1,
−1 <u≦w ≦1.5,
0≦w≦21).
7. The device according to claim 1 , wherein the medium layer is sapphire.
8. The device according to claim 1 , wherein the light emitting element is a blue LED.
9. The device according to claim 4 , wherein the element M is strontium (Sr).
10. A light emitting device comprising:
a light emitting element emitting light having wavelength of 250 nm to 500 nm;
red fluorescent layers formed above the light emitting element, each of the red fluorescent layers including a red fluorescent material, the red fluorescent layers being disposed at predetermined intervals;
a green fluorescent layer formed above the light emitting element, the green fluorescent layer including a green fluorescent material, a distance between the light emitting element and the green fluorescent layer being larger than a distance between the light emitting element and the red fluorescent layers; and
a medium layer formed on the light emitting element, the medium layer being transparent, the medium layer including projections and recesses on a surface thereof, wherein
the red fluorescent layers are formed in the recesses, and
the green fluorescent layer is formed on the projections.
11. The device according to claim 10 , wherein
a cross-section of the medium layer above an upper surfaces of the red fluorescent layers has a shape in which trapezoids are adjacent to each other with a gap “b”, a side of the light emitting element is set to a lower base, “a” is a length of the lower base, “c” is a height, and “θ” and “φ” are angles in end portions of the lower base, and
equations (1) and (2) are satisfied when n 2 is a refractive index of the medium layer while n 1 is a refractive index of a substance being in contact with two sides of the trapezoidal shape;
tan
θ
tan
ϕ
+
α
(
tan
θ
-
tan
ϕ
)
tan
θ
+
α
(
tan
θtan
ϕ
-
1
)
<
(
n
2
n
1
)
2
-
1
(
1
)
tan
θ
tan
ϕ
+
α
(
tan
ϕ
-
tan
θ
)
tan
ϕ
+
α
(
tan
θtan
ϕ
-
1
)
<
(
n
2
n
1
)
2
-
1
(
2
)
(where α=c/(a+b)).
12. The device according to claim 11 , wherein equation (3) is satisfied when both the angles θ and φ are 90 degrees and n 1 =1 and n 2 =n.
c
a
+
b
>
1
n
2
-
1
(
3
)
13. A light emitting device comprising:
a light emitting element emitting light having wavelength of 250 nm to 500 nm,
red fluorescent layers formed above the light emitting element, each of the red fluorescent layers including a red fluorescent material, the red fluorescent layers being disposed at predetermined intervals; and
a green fluorescent layer formed above the light emitting element, the green fluorescent layer including a green fluorescent material, a distance between the light emitting element and the green fluorescent layer being larger than a distance between the light emitting element and the red fluorescent layers,
wherein the red fluorescent material has a composition expressed by equation (4):
(M 1−x1 Eu x1 ) a Si b AlO c N d (4)
(In the equation (4), M is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (Aluminum), rare-earth elements, and IVB group elements x1, a, b, c, and d satisfy the following relationship:
0<x1 ≦1,
0.60<a<0.95,
2.0<b<3.9,
0.04≦c≦0.6,
4<d<5.7).
14. The device according to claim 10 , wherein the green fluorescent material has a composition expressed by equation (5):
(M′ 1−x2 Eu x2 ) 3−y Si 13−z Al 3+z O 2+u N 21−w (5)
(In the equation (5), M′ is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al (Aluminum), rare-earth elements, and IVB group elements. x2, y, z, u, and w satisfy the following relationship:
0<x2≦1,
−0.1≦y≦0.15,
−1≦z≦1,
−1< u−w ≦1.5,
0≦w≦21).
15. The device according to claim 13 , wherein the green fluorescent material has a composition expressed by the equation (5):
(M′ 1−x2 Eu x2 ) 3−y Si 13−z Al 3+z O 2+u N 21−w (5)
(In the equation (5), M′ is an element that is selected from IA group elements, IIA group elements, IIIA group elements, IIIB group elements except Al, rare-earth elements, and IVB group elements. x2, y, z, u, and w satisfy the following relationship:
0 <x2 ≦1,
−0.1 ≦y≦0.15,
−1<z<1,
−1< u−w ≦1.5,
0 ≦w≦21).
16. The device according to claim 10 , wherein the medium layer is sapphire.
17. The device according to claim 10 , wherein the light emitting element is a blue LED.
18. The device according to claim 13 , wherein the element M is strontium (Sr).