Processes for preparing color stable red-emitting phosphors
View Patent ↗Processes for preparing color stable red-emitting phosphors include contacting a complex fluoride phosphor of formula I with a first fluorine-containing oxidizing agent in gaseous form at a first temperature ranging from 200° C. to 700° C. to form a first product phosphor, contacting the first product phosphor in particulate form with a solution of a compound of formula II in aqueous hydrofluoric acid to form a treated phosphor, and contacting the treated phosphor with a second fluorine-containing oxidizing agent in gaseous form at a second temperature <225° C., A x MF y :MN 4+ I A x MF y II 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 absolute value of the charge of the MF y ion; and y is 5, 6 or 7.
1. A process comprising
contacting a complex fluoride phosphor of formula I,
A x MF y :MN 4+ I
with a first fluorine-containing oxidizing agent in gaseous form at a first temperature ranging from greater than 200° C. to about 700° C., to form a first product phosphor;
contacting the first product phosphor in particulate form with a solution of a compound of formula II in aqueous hydrofluoric acid,
A x MF y II
to form a treated phosphor; and
contacting the treated phosphor with a second fluorine-containing oxidizing agent in gaseous form at a second temperature of less than 225° C.;
wherein
A is independently at each occurrence Li, Na, K, Rb, Cs, or a combination thereof;
M independently at each occurrence 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 first and second fluorine-containing oxidizing agents are independently selected from F 2 , HF, SF 6 , BrF 5 , NH 4 HF 2 , NH 4 F, KF, AlF 3 , SbF 5 , ClF 3 , BrF 3 , KrF, XeF 2 , XeF 4 , NF 3 , SiF 4 , PbF 2 , ZnF 2 , SnF 2 , CdF 2 , C 1 -C 4 fluorocarbons, and combinations thereof.
3. A process according to claim 1 , wherein each of the first and second fluorine-containing oxidizing agent is F 2 .
4. A process according to claim 1 , wherein M independently at each occurrence is Si, Ge, Sn, Ti, Zr, or a combination thereof.
5. A process according to claim 1 , wherein
A independently at each occurrence is Na, K, Rb, Cs, or a combination thereof;
M independently at each occurrence is Si, Ge, Ti, or a combination thereof; and
y is 6.
6. A process according to claim 1 , wherein the complex fluoride phosphor is K 2 SiF 6 :Mn 4+ .
7. A process according to claim 1 , wherein the compound of formula II is K 2 SiF 6 .
8. A process according to claim 1 , wherein the first temperature is any temperature in a range from about 350° C. to about 700° C.
9. A process according to claim 1 , wherein the second temperature is any temperature in a range less than 225° C.
10. A process according to claim 1 , wherein the second temperature is any temperature in a range less than 100° C.
11. A process according to claim 1 , wherein the second temperature is about 90° C.
12. A process according to claim 1 , wherein the treated phosphor is contacted with the second fluorine-containing oxidizing agent for a period of about eight hours.
13. A process according to claim 1 , wherein the treated phosphor is contacted with the second fluorine-containing oxidizing agent for a period of about eight hours at a temperature of about 90° C.
14. A process according to claim 1 , wherein the treated phosphor is contained in a vessel having a non-metallic surface during contact with the second fluorine-containing oxidizing agent.
15. A process according to claim 14 , wherein the non-metallic surface comprises a fluoropolymer.