Light scattering and conversion plate for LEDs

1. A device comprising:

a light emitting diode;

a light scattering and conversion plate disposed in a path of light emitted by the light emitting diode, the light scattering and conversion plate comprising:

a first layer having scattering properties and essentially no conversion properties and having a thickness A; and

a second layer having conversion properties and having a thickness B, the thickness A of the first layer being greater or equal to three times the thickness B of the second layer; and

a lens disposed over the light scattering and conversion plate.

2. The device of claim 1 wherein the light emitting diode is a blue-emitting, thin film flip chip light emitting diode.

3. The device of claim 1 wherein the first layer is polycrystalline Al 2 O 3 .

4. The device of claim 1 wherein the second layer is a garnet comprising Y, Al, and O.

5. The device of claim 1 wherein the second layer is a ceramic.

6. The device of claim 1 wherein the first and second layer are connected by a silicone layer.

7. A device comprising a light scattering and conversion plate comprising:

a first layer having scattering properties and essentially no conversion properties and having a thickness A, the first layer selected from the group consisting of glass, Al 2 O 3 , Y 3 Al 5 O 12 , RE 3 Al 5 O 12 (RE=rare earth metal), Y 2 O 3 , ZnS, AlON, AlPON, AlN, MgAl 2 O 4 , SiC, SiO 2 , Si 3 N 4 and mixtures thereof; and

a second layer having conversion properties and having a thickness B, the thickness A of the first layer being greater or equal to three times the thickness B of the second layer.

8. The device of claim 7 wherein the second layer is Lu b Y c Gd d Ce e Al 5 O 12 wherein b+c+d+e=3, 0.09≤e≤0.24.

9. The device of claim 7 wherein the second layer is Ca 1−x−y−z−0.5u M x Si 1+u−v−z Al 1−u+v+z N 3−v O v :Eu y ,Ce z wherein 0≤u<0.2, 0<v<0.05, 0≤x<1, 0.001≤y≤0.01, 0.002≤y≤0.04, and M=Sr, Ba, Mg.

10. The device of claim 7 further comprising an adhesive disposed between the first and second layers.

11. The device of claim 7 wherein a scattering coefficient of the first layer is ≥100 and ≤500 cm −1 .

12. The device of claim 7 wherein a mean refractive index n of the first layer is ≥1.3 and ≤2.5.

13. The device of claim 7 wherein a difference in refractive index between the refractive index of the first layer and the second layer is ≥0.03 and ≤1.

14. A device comprising a light scattering and conversion plate comprising:

a first layer having scattering properties and essentially no conversion properties and having a thickness A; and

a second layer having conversion properties and having a thickness B, the second layer selected from the group consisting of Lu b Y c Gd d Ce e Al 5 O 12 wherein b+c+d+e=3, 0.09≤e≤0.24, Ca 1−x−y−z−0.5u M x Si 1+u−v−z Al 1−u+v+z N 3−v O v :Eu y ,Ce z wherein 0≤u<0.2, 0<v<0.05, 0≤x<1, 0.001≤y≤0.01, 0.002≤y≤0.04, and M=Sr, Ba, Mg; and mixtures thereof;

wherein the thickness A of the first layer is greater or equal to three times the thickness B of the second layer.

15. The device of claim 14 wherein the second layer is a ceramic.

16. The device of claim 14 wherein the second layer has a volume density larger than 90 percent of a main constituent, the main constituent consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 μm in diameter and having different crystallographic orientations.

17. The device of claim 16 wherein the single crystal domains are connected by one of amorphous material, glassy material, and additional crystalline constituents.

18. The device of claim 14 wherein the second layer is a ceramic having a surface roughness ≥0.005 μm and ≤0.8 μm.