Color stable red-emitting phosphors
View Patent ↗A process for synthesizing a Mn 4+ doped phosphor includes contacting a precursor of formula I, A x [MF y ]:Mn 4+ I at any temperature in a range from about 200° C. to about 700° C. with a fluorine-containing oxidizing agent in gaseous form; maintaining the temperature during a contact period of at least one hour; and, after the contact period, reducing the temperature at a rate of ≦5° C. per minute; 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; 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 any temperature in a range from about 200° C. to about 700° C. with a fluorine-containing oxidizing agent in gaseous form;
maintaining the temperature during a contact period of at least one hour; and,
after the contact period, reducing the temperature at a rate of ≦5° C. per minute;
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 1, 2, or 3, and is equal to the absolute value of the charge of the [MFy] ion;
y is 5, 6 or 7.
2. A process according to claim 1 , wherein the temperature is reduced at the rate of ≦3° C. per minute.
3. A process according to claim 1 , wherein the temperature is reduced at the rate of ≦1° C. per minute.
4. A process according to claim 1 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least one hour.
5. A process according to claim 1 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least two hours.
6. A process according to claim 1 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least three hours.
7. A process according to claim 1 , wherein the temperature is any temperature in a range from about 500° C. to about 600° C.
8. A process according to claim 1 , wherein the phosphor precursor is contacted with the fluorine-containing oxidizing agent for a period of about 8 hours.
9. A process according to claim 1 , wherein the Mn 4+ doped phosphor is K 2 SiF 6 :Mn 4+ .
10. A process for synthesizing a color stable Mn 4+ doped phosphor, the process comprising
contacting a precursor at an elevated temperature with a fluorine-containing oxidizing agent in gaseous form to form the color stable Mn 4+ doped phosphor,
maintaining the temperature during a contact period of at least one hour; and,
after the contact period, reducing the temperature at a rate of ≦5° C. per minute;
wherein the precursor is selected from the group consisting of
(A) A 2 [MF 5 ]:Mn 4+ , where A is selected from Li, Na, K, Rb, Cs, and combinations thereof; and where M is selected from Al, Ga, In, and combinations thereof;
(B) A 3 [MF 6 ]:Mn 4+ , where A is selected from Li, Na, K, Rb, Cs, and combinations thereof; and where M is selected from Al, Ga, In, and combinations thereof;
(C) Zn 2 [MF 7 ]:Mn 4+ , where M is selected from Al, Ga, In, and combinations thereof;
(D) A[In 2 F 7 ]:Mn 4+ where A is selected from Li, Na, K, Rb, Cs, and combinations thereof;
(E) A 2 [MF 6 ]:Mn 4+ , where A is selected from Li, Na, K, Rb, Cs, and combinations thereof; and where M is selected from Ge, Si, Sn, Ti, Zr, and combinations thereof;
(F) E[MF 6 ]:Mn 4+ , where E is selected from Mg, Ca, Sr, Ba, Zn, and combinations thereof; and where M is selected from Ge, Si, Sn, Ti, Zr, and combinations thereof;
(G) Ba 0.65 Zr 0.35 F 2.70 :Mn 4+ ; and
(H) A 3 [ZrF 7 ]:Mn 4+ where A is selected from Li, Na, K, Rb, Cs, and combinations thereof.
11. A process according to claim 10 , wherein the temperature ranges from about 500° C. to about 600° C.
12. A process according to claim 10 , wherein the temperature is reduced at the rate of ≦3° C. per minute.
13. A process according to claim 10 , wherein the temperature is reduced at a rate of ≦1° C. per minute.
14. A process according to claim 10 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least one hour.
15. A process according to claim 10 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least two hours.
16. A process according to claim 10 , wherein the temperature is reduced at the rate of ≦5° C. per minute for a period of at least three hours.
17. A process according to claim 10 , wherein the color stable Mn 4+ doped phosphor is K 2 SiF 6 :Mn 4+ .
18. A process according to claim 10 , wherein the temperature is any temperature in a range from about 500° C. to about 600° C.
19. A process according to claim 10 , wherein the fluorine-containing oxidizing agent is F2.