Processes for preparing color stable manganese-doped phosphors
View Patent ↗Low-HF or HF-free processes for improving color stability of a Mn +4 doped phosphor of formula I include contacting the phosphor of formula I with a solution that contains hexafluorosilicic acid, and isolating a treated phosphor of formula I having improved color stability relative to an untreated phosphor of formula I A x [MF y ]:Mn +4 (I) wherein A is Li, Na, K, Rb, Cs, R 4 or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; R is H, lower alkyl, 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 improving color stability of a Mn +4 doped phosphor of formula I,
A x [MF y ]:Mn +4 (I)
the process comprising treating the phosphor of formula I with a manganese free solution comprising hexafluorosilicic acid; and
isolating a treated phosphor having improved color stability relative to an untreated phosphor;
wherein
A is Li, Na, K, Rb, Cs, R 4 or a combination thereof;
M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;
R is H, lower alkyl, or a combination thereof;
x is 1, 2, or 3, and 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 solution additionally comprises a salt of formula A x [MF y ].
3. A process according to claim 1 , wherein the solution is free of hydrofluoric acid.
4. A process according to claim 1 , wherein the solution additionally comprises hydrofluoric acid.
5. A process according to claim 1 , additionally comprising exposing the phosphor to fluorine gas at elevated temperature.
6. A process according to claim 1 , wherein M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
7. A process according to claim 1 , wherein the Mn +4 doped phosphor is K 2 SiF 6 :Mn +4 .
8. A process for improving color stability of a complex fluoride compound of formula K 2 SiF 6 :Mn +4 , the process comprising treating the phosphor with a manganese free solution comprising hexafluorosilicic acid; and isolating a treated phosphor formula K 2 SiF 6 :Mn +4 having improved color stability relative to an untreated phosphor formula K 2 SiF 6 :Mn +4 .
9. A process according to claim 8 , wherein the solution additionally comprises K 2 SiF 6 .
10. A process according to claim 8 , wherein the solution is free of hydrofluoric acid.
11. A process according to claim 8 , wherein the solution additionally comprises hydrofluoric acid.
12. A process according to claim 8 , additionally comprising exposing the phosphor to fluorine gas at elevated temperature.