Light emitting device

1. A light emitting device comprising:

a board;

a plurality of first light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a plurality of second light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a first fluorescent layer formed on each of the first light emitting elements, the first fluorescent layer including a first phosphor; and

a second fluorescent layer formed on each of the second light emitting elements, the second fluorescent layer including a second phosphor being higher than the first phosphor in luminous efficiency at 50° C., being lower than the first phosphor in the luminous efficiency at 150° C.,

wherein the first light emitting elements are mounted on a first region of the board,

the second light emitting elements are mounted on a second region of the board, and

the first region has higher rate of increase in temperature than that of the second region.

2. A light emitting device comprising:

a board;

a plurality of first light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a plurality of second light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a first fluorescent layer formed on each of the first light emitting elements, the first fluorescent layer including a first phosphor; and

a second fluorescent layer formed on each of the second light emitting elements, the second fluorescent layer including a second phosphor being higher than the first phosphor in luminous efficiency at 50° C., being lower than the first phosphor in the luminous efficiency at 150° C.,

wherein packaging density of the first light emitting elements in a first region of the board is higher than that of the second light emitting elements in a second region.

3. A light emitting device comprising:

a board;

a plurality of first light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a plurality of second light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a first fluorescent layer formed on each of the first light emitting elements, the first fluorescent layer including a first phosphor; and

a second fluorescent layer formed on each of the second light emitting elements, the second fluorescent layer including a second phosphor being higher than the first phosphor in luminous efficiency at 50° C., being lower than the first phosphor in the luminous efficiency at 150° C.,

wherein the first light emitting elements are mounted on a first region of the board,

the second light emitting elements are mounted on a second region of the board, and

wherein the first region is surrounded by the second region.

4. A light emitting device comprising:

a board;

a plurality of first light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a plurality of second light emitting elements mounted on the board to emit light having a wavelength of 250 nm to 500 nm;

a first fluorescent layer formed on each of the first light emitting elements, the first fluorescent layer including a first phosphor; and

a second fluorescent layer formed on each of the second light emitting elements, the second fluorescent layer including a second phosphor being higher than the first phosphor in luminous efficiency at 50° C., being lower than the first phosphor in the luminous efficiency at 150° C.,

wherein the first light emitting elements are mounted on a first region of the board,

the second light emitting elements are mounted on a second region of the board, and

wherein a thermal resistance of the board in the first region is larger than that of the board in the second region.

5. The device according to claim 1 , wherein white-color light is emitted by the first light emitting element and the first fluorescent layer, and white-color light is emitted by the second light emitting element and the second fluorescent layer.

6. The device according to claim 1 , wherein the first light emitting element or the second light emitting element is a semiconductor light emitting element that emits ultraviolet light or blue light.

7. The device according to claim 1 , wherein the first phosphor has a composition expressed by equation (1) or equation (2), and the second phosphor has a composition expressed by equation (3):

(M 1−x1 Eu x1 ) 3−y1 Si 13−z1 O 2+u N 21−w   (1)

(In the equation (1), 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, and x1, y1, z1, u, and w satisfy the following relationship:

0< x 1<1,

−0.1< y 1<0.3,

−3< z 1≦1,

−3< u−w≦ 1.5)

(M′ 1−x2 Eu x2 ) a1 Si b1 AlO c1 N d1   (2)

(In the equation (2), 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, and x2, a1, b1, c1, and d1 satisfy the following relationship:

0< x 2<1,

0.55< a 1 <0.95,

2.0< b 1<3.9,

0< c 1<0.6,

4< d 1<5.7)

(Ba 1−y2−z2−x3 Ca y2 Sr z2 Eu x3 ) a2 Si b2 O c2   (3)

(In the equation (3), x3, y2, z2, a2, b2, and c2 satisfy the following relationship:

0< x 3≦1,

0≦ y 2≦1,

0≦ z 2≦1,

1.5≦ a 2<2.5,

0.5< b 2<1.5,

3.5< c 2<4.5).

8. The device according to claim 7 , wherein the second fluorescent layer becomes a temperature of 100 ° C. or less in a usage state.

9. The device according to claim 7 , wherein white-color light is emitted by the first light emitting element and the first fluorescent layer, and white-color light is emitted by the second light emitting element and the second fluorescent layer.

10. The device according to claim 7 , wherein the first light emitting element or the second light emitting element is a semiconductor light emitting element that emits ultraviolet light or blue light.

11. The device according to claim 4 , wherein the first phosphor has a composition expressed by equation (1) or equation (2), and the second phosphor has a composition expressed by equation (3):

(M 1−x1 Eu x1 ) 3−y1 Si 13−z1 Al 3+z1 O 2+u N 21−w   (1)

(In the equation (1), 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, and x1, y1, z1, u, and w satisfy the following relationship:

0< x 1<1,

−0.1< y 1<0.3,

−3< z 1≦1,

−3< u−w≦ 1.5)

(M′ 1−x2 Eu x2 ) a1 Si b1 AlO cl N d1   (2)

(In the equation (2), 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, and x2, a1, b1, c1, and d1 satisfy the following relationship:

0< x 2<1,

−0.55< a 1<0.95,

2.0< b 1<3.9,

0< c 1 <0.6,

4< d 1<5.7)

(Ba 1−y2−z2−x3 Ca y2 Sr z2 Eu x3 ) a2 Si b2 O c2   (3)

(In the equation (3), x3, y2, z2, a2, b2, and c2 satisfy the following relationship:

0< x 3≦1,

0≦ y 2≦1,

0≦ z 2≦1,

1.5< a 2<2.5,

0.5< b 2<1.5,

3.5< c 2<4.5).

12. The device according to claim 11 , wherein the second fluorescent layer becomes a temperature of 100° C. or less in a usage state.

13. The device according to claim 11 , wherein white-color light is emitted by the first light emitting element and the first fluorescent layer, and white-color light is emitted by the second light emitting element and the second fluorescent layer.

14. The device according to claim 2 , wherein the first phosphor has a composition expressed by equation (1) or equation (2), and the second phosphor has a composition expressed by equation (3):

(M 1−x1 Eu x1 ) 3−y1 Si 13−z1 Al 3+z1 O 2+u N 21−w   (1)

(In the equation (1), 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, and x1, y1, z1, u, and w satisfy the following relationship:

0< x 1<1,

−0.1< y 1<0.3,

−3< z 1≦1,

−3< u−w ≦1.5)

(M′ 1−x2 Eu x2 ) a1 Si b1 AlO c1 N d1   (2)

(In the equation (2), 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, and x2, a1, b1, c1, and d1 satisfy the following relationship:

0< x 2<1,

0.55< a 1<0.95,

2.0< b 1<3.9,

0< c 1<0.6,

4< d 1<5.7)

(Ba 1−y2−z2−x3 Ca y2 Sr z2 Eu x3 ) a2 Si b2 O c2   (3)

(In the equation (3), x3, y2, z2, a2, b2, and c2 satisfy the following relationship:

0< x 3≦1,

0≦ y 2≦1,

0≦ z 2≦1,

1.5< a 2<2.5,

0.5< b 2<1.5,

3.5< c 2<4.5).

15. The device according to claim 14 , wherein the second fluorescent layer becomes a temperature of 100° C. or less in a usage state.

16. The device according to claim 14 , wherein white-color light is emitted by the first light emitting element and the first fluorescent layer, and white-color light is emitted by the second light emitting element and the second fluorescent layer.

17. The device according to claim 3 , wherein the first phosphor has a composition expressed by equation (1) or equation (2), and the second phosphor has a composition expressed by equation (3):

(M 1−x1 Eu x1 ) 3−y1 Si 13−z1 Al 3+z1 O 2+u N 21−w   (1)

In the equation (1), 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, and x1, y1, z1, u, and w satisfy the following relationship:

0< x 1<1,

−0.1< y 1<0.3,

−3< z 1≦1,

−3< u−w ≦1.5)

(M′ 1−x2 Eu x2 ) a1 Si b1 AlO c1 N d1   (2)

(In the equation (2), 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, and x2, a1, b1, c1, and d1 satisfy the following relationship:

0< x 2<1,

0.55< a 1<0.95,

2.0< b 1<3.9,

b 0 < c 1<0.6,

4< d 1<5.7)

(Ba 1−y2−z2−x3 Ca y2 Sr z2 Eu x3 ) a2 Si b2 O c2   (3)

(In the equation (3), x3, y2, z2, a2, b2, and c2 satisfy the following relationship:

0< x 3≦1,

0≦ y 2≦1,

0≦ z 2≦1,

1.5< a 2<2.5,

0.5< b 2<1.5,

3.5< c 2<4.5).

18. The device according to claim 17 , wherein the second fluorescent layer becomes a temperature of 100° C. or less in a usage state.

19. The device according to claim 17 , wherein white-color light is emitted by the first light emitting element and the first fluorescent layer, and white-color light is emitted by the second light emitting element and the second fluorescent layer.