Wavelength converted light emitting device
In a method according to embodiments of the invention, for a predetermined amount of light produced by a light emitting diode and converted by a phosphor layer comprising a host material and a dopant, and for a predetermined maximum reduction in efficiency of the phosphor at increasing excitation density, a maximum dopant concentration of the phosphor layer is selected.
1. A structure comprising: a blue light emitting diode; and
a yellow-green ceramic phosphor comprising phosphor particles having an average diameter disposed in a path of light emitted by the light emitting diode, each phosphor particle comprises:
a first region at the center of the particle, having a first dopant concentration; and a second region at the outer portion of the particle, having a second dopant concentration;
the second dopant concentration is less than the first dopant concentration.
2. The structure of claim 1 wherein the first dopant concentration is a highest dopant concentration in the phosphor particle.
3. The structure of claim 2 wherein the second dopant concentration is graded along a portion of the average diameter of each phosphor particle.
4. The structure of claim 3 wherein the dopant is Europium.
5. The structure of claim 1 wherein the phosphor particles are formed by providing a doped core, growing a non-doped shell around the doped core, and diffusing the dopant in a thermal process partially into the outer region.
6. The structure of claim 1 wherein the average diameter is no greater than 20 μm.
7. The structure of claim 1 wherein the average diameter is at least 2 μm.
8. The structure of claim 1 wherein the average diameter is no greater than 50 μm.
9. The structure of claim 1 wherein the second dopant concentration is graded along a portion of the average diameter of each phosphor particle.
10. The structure of claim 1 wherein the dopant is any of Europium, Eu 2+ , Cerium, Ce 3+ .
11. The structure of claim 1 wherein the phosphor particles are spherical.
12. The structure of claim 1 wherein the dopant is Europium.
13. The structure of claim 1 wherein the yellow-green ceramic phosphor is attached to the blue light emitting diode.
14. The structure of claim 1 wherein an average spacing between dopants is at least 15 Å.
15. The structure of claim 1 wherein an average spacing between dopants is at least 18 Å.
16. The structure of claim 1 wherein an average spacing between dopants is at least 20 Å.
17. The structure of claim 1 wherein an average spacing between dopants is at least 25 Å.