Color stable manganese-doped phosphors
View Patent ↗A lighting apparatus capable of emitting white light includes a semiconductor light source; and a phosphor material radiationally coupled to the light source. The phosphor material includes a color-stable Mn +4 doped phosphor prepared by a process including 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.
1. A lighting apparatus comprising
a semiconductor light source; and
a phosphor material radiationally coupled to the light source and comprising a color-stable Mn +4 doped phosphor prepared by a 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, 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.
2. A lighting apparatus according to claim 1 , wherein M is Si, Ge, Sn, Ti, Zr, or a combination thereof.
3. A lighting apparatus according to claim 1 , wherein the compound of formula III is (NR 4 ) 2 [MF 6 ] and the compound of formula IV is A 2 [MnF 6 ].
4. A process according to claim 3 , wherein the compound of formula III is (NH 4 ) 2 SiF 6 and the compound of formula IV is K 2 MnF 6 .
5. A lighting apparatus 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.
6. A lighting apparatus 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.
7. A lighting apparatus 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;
whereby the Mn +4 doped phosphor is precipitated from the combined solutions in particulate form.
8. A lighting apparatus according to claim 7 , wherein A is K, Na, or a combination thereof.
9. A lighting apparatus according to claim 7 , wherein the compound of formula III is (NR 4 ) 2 [MF 6 ] and the compound of formula IV is A 2 [MnF 6 ].
10. A lighting apparatus according to claim 7 , wherein the compound of formula III is (NH 4 ) 2 SiF 6 and the compound of formula IV is K 2 MnF 6 .