Phosphor composition
A method is disclosed for forming a blended phosphor composition. The method includes the steps of firing precursor compositions that include europium and nitrides of at least calcium, strontium and aluminum, in a refractory metal crucible and in the presence of a gas that precludes the formation of nitride compositions between the nitride starting materials and the refractory metal that forms the crucible. The resulting compositions can include phosphors that convert frequencies in the blue portion of the visible spectrum into frequencies in the red portion of the visible spectrum.
1. A method of making a phosphor composition, the method comprising:
forming a mixture comprising:
a cation selected from the group consisting of calcium, strontium, lithium, sodium, potassium, rubidium, cesium, magnesium, barium, scandium, yttrium, lanthanum, gadolinium, and lutetium;
a cation selected from the group consisting of aluminum, silicon, boron, gallium, carbon, germanium, and phosphorus;
an anion selected from the group consisting of nitrogen, sulfur, chlorine, bromine, and iodine; and
an activator selected from the group consisting of europium (II); cerium (III), ytterbium (II), samarium (II) and manganese (II);
heating the mixture in the presence of a forming gas; and
forming from the mixture a phosphor composition including at least a first phase,
wherein, when the phosphor composition is exposed to Kα x-rays from Cu, the first phase exhibits maximum intensity diffraction peaks at 20 values of about 31.5°, about 35.0°, and about 36.1°.
2. The method of claim 1 , wherein the first phase comprises Ca 1-x-y Sr x Eu y AlSiN 3 , where 0<x<1 and 0<y<1.
3. The method of claim 2 , wherein x is between 0.50 and 0.70.
4. The method of claim 3 , wherein x is between about 0.55 and 0.67.
5. The method of claim 2 , wherein y is between about 0.013 and 0.017.
6. The method of claim 1 , wherein the phosphor composition further comprises a second phase, and wherein, when the phosphor composition is exposed to Kα x-rays from Cu, the second phase exhibits maximum intensity diffraction peaks at 20 values of about 26.6° and about 32.6°.
7. The method of claim 6 , wherein the second phase comprises a silicon aluminum oxynitride.
8. The method of claim 7 , wherein the silicon aluminum oxynitride comprises Si 2 Al 4 O 4 N 4 .
9. The method of claim 6 , wherein the phosphor composition further comprises a third phase, and wherein, when the phosphor composition is exposed to Kα x-rays from Cu, the third phase exhibits maximum intensity diffraction peaks at 20 values of about 33.2° and about 37.9°.
10. The method of claim 9 , wherein the third phase comprises AlN.
11. The method of claim 9 , wherein the phosphor composition further comprises a fourth phase, and wherein, when the phosphor composition is exposed to Kα x-rays from Cu, the fourth phase exhibits a maximum intensity diffraction peak at a 20 value of about 44.2°.
12. The method of claim 1 , wherein the phosphor composition absorbs wavelengths of between about 430 and 480 nanometers and emits peak wavelengths of between about 530 and 750 nanometers.
13. The method of claim 1 , wherein heating the mixture comprises firing at a temperature of between about 1500 and 1800° C.
14. The method of claim 1 , wherein heating the mixture includes at least three heating steps at increasingly higher temperatures.
15. The method of claim 14 , wherein the at least three heating steps include a one hour heating step at 800° C., a one hour heating step at 1200° C., and a two hour heating step at 1675° C.
16. The method of claim 15 , further comprising ramping steps of 350° C. per hour between the heating steps.
17. The method of claim 1 wherein the mixture is heated in the substantial absence of water and oxygen.
18. The method of claim 1 wherein the mixture is heated in a refractory crucible that is substantially inert in the presence of the forming gas.
19. The method of claim 1 , wherein the forming gas comprises about 95% nitrogen and about 5% hydrogen.
20. The method of claim 1 , wherein the mixture includes Ca 3 N 2 , Sr 2 N, AlN and Si 3 N 4 .