Color stable manganese-doped phosphors
View Patent ↗A process for preparing color stable Mn +4 doped phosphors includes providing a phosphor of formula I; A x [MF y ]:Mn +4 I and contacting the 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 Li, Na, K, Rb, Cs, NR 4 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; R is H, lower alkyl, 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 particular embodiments, M is Si, Ge, Sn, Ti, Zr, or a combination thereof. A lighting apparatus capable of emitting white light includes a semiconductor light source; and a phosphor composition radiationally coupled to the light source, and which includes a color stable Mn +4 doped phosphor.
1. A process for preparing a color-stable Mn +4 doped phosphor, said process comprising
providing a Mn +4 doped phosphor of formula I; and
A x [MF y ]:Mn +4 I
contacting the 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 Li, Na, K, Rb, Cs, R 4 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;
R is H, lower alkyl, 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 M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
3. A process according to claim 1 , wherein the Mn +4 doped phosphor is K 2 SiF 6 :Mn +4 and the composition of formula II is K 2 SiF 6 .
4. A process according to claim 1 , wherein the step of contacting is performed at a temperature ranging from about 20° C. to about 50° C.
5. A process according to claim 1 , wherein the step of contacting is performed for a time ranging from about one minute to about five hours.
6. A process according to claim 1 , wherein the time ranges from about five minutes to about one hour.
7. A process according to claim 1 , wherein providing the Mn +4 doped phosphor comprises
providing a solution of the phosphor of formula I in aqueous hydrofluoric acid at a temperature greater than about 60° C.; and
cooling the solution to a temperature less than about 30° C.;
whereby the phosphor is precipitated from the solution in particulate form.
8. A process according to claim 1 , wherein providing the providing the Mn +4 doped phosphor comprises
providing an solution comprising the phosphor of formula I and aqueous hydrofluoric acid; and
maintaining the solution at a temperature ranging from about 25° C. to about 120° C. while evaporating solvent of the solution;
whereby the phosphor is precipitated from the solution in particulate form.
9. A process according to claim 1 , wherein providing the Mn +4 doped phosphor comprises
providing a first aqueous hydrofluoric acid solution comprising a compound of formula III and a compound of formula IV; and
(NR 4 ) x [MF y ] III
A x [MnF y ] IV
combining the first solution with a second aqueous hydrofluoric acid solution comprising excess A + ions; and
whereby the Me doped phosphor is precipitated from the combined solutions in particulate form.
10. A process according to claim 9 , wherein A is K, Na, or a combination thereof.
11. A process according to claim 9 , wherein the compound of formula III is (NR 4 ) 2 [MF 6 ] and the compound of formula IV is A 2 [MnF 6 ].
12. A process according to claim 9 , wherein the compound of formula III is (NH 4 ) 2 SiF 6 and the compound of formula IV is K 2 MnF 6 .
13. A color-stable Mn +4 doped phosphor prepared by a process according to claim 1 .
14. A phosphor blend comprising a color-stable Mn +4 doped phosphor prepared by a process according to claim 1 .