Processes for preparing color stable red-emitting phosphor particles having small particle size
A process for preparing a Mn +4 doped phosphor of formula I A x [MF y ]:Mn +4 I includes combining a first solution comprising a source of A and a second solution comprising H 2 MF 6 in the presence of a source of Mn, to form the 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, 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; and wherein a value of a Hammett acidity function of the first solution is at least −0.9. Particles produced by the process may have a particle size distribution with a D 50 particle size of less than 10 μm.
1. A process for preparing a Mn +4 doped phosphor of formula I
A x [MF y ]:Mn +4 I
the process comprising combining a first solution comprising a source of A and a second solution comprising H 2 MF 6 in the presence of a source of Mn, to form the 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, 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; and
wherein a value of a Hammett acidity function of the first solution is at least −0.9; and
wherein at least one of the first solution and the second solution additionally comprises a surfactant.
2. A process according to claim 1 , wherein the value of the Hammett acidity function of the first solution is at least −0.5.
3. A process according to claim 1 , wherein concentration of the source of A in the first solution is at least 6M.
4. A process according to claim 1 , wherein the concentration of the source of A in the first solution is at least 7.8M.
5. A process according to claim 1 , wherein a molar ratio of A to M is at least 7/1.
6. A process according to claim 1 , wherein a molar ratio of A to M is at least 9/1.
7. A process according to claim 1 , wherein the first and second solutions are combined over a period of 10 seconds or less.
8. A process according to claim 1 , wherein the source of A is KF.
9. A process according to claim 1 , wherein the first solution is free of HF.
10. A process according to claim 1 , wherein the phosphor of formula I is K 2 SiF 6 :Mn.
11. A process for preparing a Mn +4 doped phosphor of formula I,
A x [MF y ]:Mn +4 I
the process comprising
gradually adding a first solution comprising a source of A and a second solution comprising a source of a source of M to a reactor in the presence of a source of Mn, to form a product liquor comprising the Mn +4 doped phosphor; and
gradually discharging the product liquor from the reactor;
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;
y is 5, 6 or 7; and
wherein
a value of a Hammett acidity function of the first solution is at least −1.3;
a value of a Hammett acidity function of the second solution is at least −3;
a ratio of a volume of a 35% H 2 SiF 6 solution to a volume of a 48% HF solution in the second solution is at least 1:2.5; and
wherein at least one of the first solution and the second solution additionally comprises a surfactant.
12. A process according to claim 11 , wherein the product liquor is gradually discharged from the reactor while maintaining a volume thereof at less than 100 ml.
13. A process according to claim 11 , wherein the value of the Hammett acidity function of the first solution is at least −0.9.
14. A process according to claim 11 , wherein the source of A is KF.