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 light emitting diode (LED) configured to emit light having a first peak wavelength; and
a phosphor configured to absorb light emitted by the LED and emit light having a second peak wavelength, the phosphor comprising:
a host material and a dopant;
a first phosphor region comprising a first external phosphor surface facing the LED, the first phosphor region having a first non-zero dopant concentration of the dopant, the first external phosphor surface not disposed in direct contact to any phosphor comprising a same material as the host material and disposed outside the first phosphor region;
a second phosphor region comprising a second external phosphor surface oppositely positioned from the first external phosphor surface, the second phosphor region having a second non-zero dopant concentration of the dopant greater than the first non-zero dopant concentration and arranged further from the LED than the first phosphor region, the second external phosphor surface not disposed in direct contact to any phosphor comprising a same material as the host material and disposed outside the second phosphor region.
2. The structure of claim 1 wherein the first and second regions comprise first and second layers.
3. The structure of claim 2 wherein the dopant concentration is graded between the second and first layers.
4. The structure of claim 1 , wherein the phosphor includes multiple layers of different dopant concentration.
5. The structure of claim 4 , wherein the dopant concentration within each of the layers is constant and uniform.
6. The structure of claim 1 wherein the dopant is any of Europium, Eu2+, Cerium, Ce3+.
7. The structure of claim 1 wherein LED is configured to emit blue light and the phosphor is configured to emit yellow or green light.
8. The structure of claim 1 wherein the phosphor is a ceramic phosphor.
9. A structure comprising:
a light emitting diode (LED), and
phosphor particles having an average diameter disposed in a path of light emitted by the LED, each phosphor particle comprising a dopant and:
a core having a concentration gradient of the dopant with a first non-zero dopant concentration range, the concentration gradient continuously decreasing from a center of the core, and
a shell surrounding the core having a second non-zero dopant concentration of the dopant less than the first non-zero dopant concentration range.
10. The structure of claim 9 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.
11. The structure of claim 9 wherein the average diameter is no greater than 20 μm.
12. The structure of claim 9 wherein the average diameter is at least 2 μm.
13. The structure of claim 9 wherein the average diameter is no greater than 50 μm.
14. The structure of claim 9 wherein the dopant concentration is graded along a portion of the average diameter of each phosphor particle.
15. The structure of claim 9 wherein the dopant is any of Europium, Eu2+, Cerium, Ce3+.
16. The structure of claim 9 wherein the phosphor particles are spherical.
17. The structure of claim 9 wherein LED is configured to emit blue light and the phosphor particles are configured to emit yellow or green light.
18. The structure of claim 9 wherein the phosphor particles are ceramic phosphor particles.