Color stable red-emitting phosphors
A process for preparing a Mn +4 doped phosphor of formula I includes gradually adding a first solution comprising a source of M and HF and a second solution comprising a source of Mn to a reactor, in the presence of a source of A and an anion selected from phosphate, sulfate, acetate, and combinations thereof, to form a product liquor comprising the Mn +4 doped phosphor. The process also includes gradually discharging the product liquor from the reactor while volume of the product liquor in the reactor remains constant. A is Li, Na, K, Rb, Cs, 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; x is the absolute value of the charge of the [MF y ] ion; and y is 5, 6 or 7.
1. A process for preparing a Mn +4 doped phosphor of formula I
the process comprising gradually adding a first solution comprising a source of M and HF and a second solution comprising a source of Mn to a reactor, in the presence of a source of A and an anion selected from phosphate, sulfate, acetate, and combinations thereof, to form a product liquor comprising the Mn+4 doped phosphor; and
gradually discharging the product liquor from the reactor while volume of the product liquor in the reactor remains approximately constant;
wherein
A is Li, Na, K, Rb, Cs, 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;
x is the absolute value of the charge of the [MF y ] ion; and
y is 5, 6 or 7.
2. The process according to claim 1 , wherein gradually adding the first solution and the second solution in the presence of the source of A and the anion includes adding the first solution and the second solution in the presence of the source of A and potassium sulfate, potassium acetate, or a combination thereof.
3. The process according to claim 1 , wherein gradually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion includes continually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion.
4. The process according to claim 1 , wherein gradually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion includes semi-continually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion.
5. The process according to claim 1 , further comprising an initial period wherein the first and second solutions are gradually added to the reactor without discharging the product liquor.
6. The process according to claim 1 , additionally comprising precharging the reactor with a material selected from HF, the source of A, preformed particles of the Mn +4 doped phosphor, or a combination thereof.
7. The 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 .
8. The process according to claim 1 , wherein the Mn +4 doped phosphor of formula I is K 2 SiF 6 : Mn 4+ .
9. A Mn +4 doped phosphor of formula I prepared by a process according to claim 1 .
10. A lighting apparatus comprising a Mn +4 doped phosphor according to claim 9 .
11. A backlight device comprising a Mn +4 doped phosphor according to claim 9 .
12. A process for preparing a Mn +4 doped phosphor of formula I
the process comprising gradually adding a first solution comprising a source of M and HF and a second solution comprising a source of Mn to a reactor, in the presence of a source of A and a source of an anion selected from phosphate, sulfate, acetate, and combinations thereof, to form a product liquor comprising the Mn +4 doped phosphor, wherein the source of the anion is an acid, an acetate, or a combination thereof; and
gradually discharging the product liquor from the reactor while volume of the product liquor in the reactor remains approximately constant;
wherein
A is Li, Na, K, Rb, Cs, 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
x is the absolute value of the charge of the [MF y ] ion; and
y is 5, 6 or 7.
13. The process according to claim 12 , wherein the source of the anion is sulfuric acid, phosphoric acid, or a combination thereof.
14. The process according to claim 12 , wherein the source of the anion is potassium sulfate, potassium acetate, or a combination thereof.
15. The process according to claim 12 , wherein gradually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion includes continually adding the first solution and the second solution to the reactor in the presence of the source of A and the source of the anion.
16. The process according to claim 12 , wherein gradually adding the first solution and the second solution to the reactor in the presence of the source of A and the anion includes semi-continually adding the first solution and the second solution to the reactor in the presence of the source of A and the source of the anion.
17. The process according to claim 12 , wherein:
A is Na, K, Rb, Cs, or a combination thereof;
M is Si, Ge, Ti, or a combination thereof; and
Y is 6 .
18. The process according to claim 12 , wherein the Mn +4 doped phosphor of formula I is K 2 SiF 6 : Mn 4+ .