Processes for preparing color stable red-emitting phosphors
View Patent ↗Processes for preparing color stable Mn 4+ doped phosphors include contacting a phosphor of formula I with a fluorine-containing oxidizing agent in gaseous form at temperature ≦225° C. to form the color stable Mn 4+ doped phosphor A x MF y : Mn 4 + I wherein A is independently at each occurrence Li, Na, K, Rb, Cs, or a combination thereof; M is independently at each occurrence 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. In another aspect, the processes include contacting a phosphor of formula I at an elevated temperature with an oxidizing agent comprising a C 1 -C 4 fluorocarbon, to form the color stable Mn 4+ doped phosphor.
1. A process for synthesizing a color stable Mn 4+ doped phosphor, the process comprising
contacting a phosphor of formula I,
A
x
MF
y
:
Mn
4
+
I
with a fluorine-containing oxidizing agent in gaseous form at a temperature from 90° C. to less than 225° C. to form the color stable Mn 4+ 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 , SbF 5 , ClF 3 , BrF 3 , KrF, XeF 2 , XeF 4 , NF 3 , or a combination thereof.
3. A process according to claim 1 , wherein the fluorine-containing oxidizing agent comprises F 2 .
4. A process according to claim 1 , wherein M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
5. 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.
6. A process according to claim 1 , wherein the phosphor is K 2 SiF 6 :Mn 4+ .
7. 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
8. A process for synthesizing a color stable Mn 4+ doped phosphor, the process comprising contacting a phosphor of formula I,
A
x
MF
y
:
Mn
4
+
I
at an elevated temperature with a fluorine-containing oxidizing agent to form the color stable Mn 4+ doped phosphor, the fluorine-containing oxidizing agent comprises a compound selected from the group consisting of: F 2 , anhydrous HF, BrF 5 , NH 4 F, AlF 3 , SF 6 , SbF 5 , ClF 3 , KrF, XeF 4 , NF 3 , PbF 2 , ZnF 2 , SiF 4 , SnF 2 , CdF 2 , a C 1 -C 4 fluorocarbon and a combination thereof; and
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
wherein
A is independently at each occurrence Li, Na, K, Rb, Cs, NR 4 or a combination thereof;
M is independently at each occurrence Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;
R is H, lower alkyl, or a combination thereof;
x is independently at each occurrence the absolute value of the charge of the MF y ion; and
y is independently at each occurrence 5, 6 or 7.
9. A process according to claim 8 , wherein the temperature ranges from about 200° C. to about 700° C.
10. A process according to claim 8 , wherein the temperature ranges from about 350° C. to about 600° C.
11. A process according to claim 8 , wherein the phosphor is contacted with the fluorine-containing oxidizing agent for a period of at least four hours.
12. A process according to claim 8 , wherein M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
13. A process according to claim 8 , wherein
A is Na, K, Rb, Cs, or a combination thereof;
M is Si, Ge, Ti, or a combination thereof; and
Y is 6.
14. A process according to claim 8 , wherein the phosphor is K 2 SiF 6 :Mn 4+ .
15. A process according to claim 8 , wherein the fluorine-containing oxidizing agent is a C 1 -C 4 fluorocarbon.
16. A process according to claim 15 , wherein the fluorine-containing oxidizing agent further comprises F 2 .
17. A process according to claim 15 , wherein the C 1 -C 4 fluorocarbon is selected from CF 4 , C 2 F 6 , C 3 F 8 , C 2 H 2 F 4 , C 2 HF 3 , and combinations thereof.
18. The process according to claim 17 , wherein the C 1 -C 4 fluorocarbon is CF 4 .