Color stable red-emitting phosphors
View Patent ↗A process for synthesizing a color stable Mn 4+ doped phosphor includes contacting a precursor of formula I, in gaseous form at an elevated temperature with a fluorine-containing oxidizing agent to form the color stable Mn 4+ doped phosphor A x [MF y ]:Mn 4+ I wherein A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MF y ] ion; and y is 5, 6 or 7.
1. A process for synthesizing a color stable Mn 4+ doped phosphor, the process comprising contacting a precursor of formula I,
A x [MF y ]:Mn 4+ I
at an elevated temperature with a fluorine-containing oxidizing agent in gaseous form to form the color stable Me doped phosphor;
wherein
A is Li, Na, K, Rb, Cs, or a combination thereof;
M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;
x is the absolute value of the charge of the [MF y ] ion; and
y is 5, 6 or 7.
2. A process according to claim 1 , wherein the fluorine-containing oxidizing agent is F 2 , anhydrous HF, BrF 5 , NH 4 HF 2 , NH 4 F, AlF 3 , SF 6 , SbF 5 , ClF 3 , BrF 3 , KrF, XeF 2 , XeF 4 , NF 3 , PbF 2 , ZnF 2 , SiF 4 , SnF 2 , CdF 2 or a combination thereof.
3. A process according to claim 1 , wherein the fluorine-containing oxidizing agent is F 2 .
4. A process according to claim 1 , wherein the temperature is at least 100° C.
5. A process according to claim 1 , wherein the temperature is at least 350° C.
6. A process according to claim 1 , wherein the temperature is at least 225° C.
7. A process according to claim 1 , wherein the temperature is any temperature in a range from about 200° C. to about 700° C.
8. A process according to claim 1 , wherein the temperature is any temperature in a range from about 350° C. to about 600° C.
9. A process according to claim 1 , wherein the phosphor precursor is contacted with the reactant for a period of at least one hour.
10. A process according to claim 1 , wherein the phosphor precursor is contacted with the reactant for a period of at least four hours.
11. A process according to claim 1 , wherein the phosphor precursor is contacted with the reactant for a period of least about six hours.
12. A process according to claim 1 , wherein the phosphor precursor is contacted with the reactant for a period of about eight hours.
13. A process according to claim 1 , wherein the phosphor precursor is contacted with the reactant for a period of at least eight hours and a temperature of at least 250° C.
14. A process according to claim 1 , wherein the temperature is initially about 250° C. for about four hours and then about 350° C. for about four hours.
15. A process according to claim 1 , wherein the atmosphere comprises at least 0.5% fluorine.
16. A process according to claim 1 , wherein the atmosphere comprises at least 5% fluorine.
17. A process according to claim 1 , wherein the atmosphere comprises at least 20% fluorine.
18. A process according to claim 1 , wherein the atmosphere additionally comprises nitrogen, helium, neon, argon, krypton, xenon, or a combination thereof.
19. A process according to claim 1 , wherein the atmosphere comprises about 20% fluorine and about 80% nitrogen.
20. A process according to claim 1 , wherein M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
21. A process according to claim 1 , wherein
A is Na, K, Rb, Cs, or a combination thereof;
M is Si, Ge, Ti, or a combination thereof; and
Y is 6.
22. A process according to claim 1 , wherein the phosphor precursor is K 2 SiF 6 :Mn 4+ .
23. A process according to claim 1 , additionally comprising contacting the color stable Mn 4+ doped phosphor in particulate form with a saturated solution of a composition of formula II in aqueous hydrofluoric acid,
A x [MF y ]; II.
24. A color stable Mn 4+ doped phosphor prepared by a process according to claim 1 .
25. A lighting apparatus comprising a semiconductor light source; and color stable Mn 4+ doped phosphor prepared by a process according to claim 1 .
26. A lighting apparatus according to claim 25 , having a color shift of ≦1.5 MacAdam ellipses after operating for at least 2,000 hour at a LED current density greater than 2 A/cm 2 , a LED wall-plug efficiency greater than 40%, and a board temperature greater than 25° C.
27. A lighting apparatus according to claim 26 , wherein the MacAdam ellipse color shift is ≦1.
28. A lighting apparatus according to claim 26 , having a color shift of ≦2 MacAdam ellipses after operating for 30 minutes at a LED current density greater than 70 A/cm 2 , a LED wall-plug efficiency greater than 18%, and a board temperature greater than 25° C.
29. A backlight device comprising a semiconductor light source; and a color stable Mn 4+ doped phosphor prepared by a process according to claim 1 .