Coated red line emitting phosphors
A process for coating a phosphor of formula I: A x [MF y ]:Mn 4+ includes combining the phosphor of formula I in particulate form with a first solution including a compound of formula II: A x [MF y ] to form a suspension and combining a second solution with the suspension, the second solution including a precursor including an element selected from the group consisting of calcium, strontium, magnesium, yittrium, barium, scandium, lanthanum, and combinations thereof. A population of particles having a core including a phosphor of formula I and a manganese-free composite coating disposed on the core, and a lighting apparatus ( 10 ) including the population of particles are also presented.
1. A process comprising:
combining a phosphor of formula I in particulate form with a first solution comprising a compound of formula II to form a suspension; and combining a second solution with the suspension, the second solution comprising a precursor comprising an element selected from the group consisting of calcium, strontium, magnesium, barium, yttrium, scandium, lanthanum, and combinations thereof,
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 an absolute value of a charge of the [MF y ] ion; and
y is 5, 6 or 7.
2. The process according to claim 1 , wherein the precursor additionally comprises an anion selected from halide, hydroxide, nitrate, acetate, MF y or a combination thereof.
3. The process according to claim 1 , wherein the precursor is calcium chloride, strontium chloride, magnesium chloride, yttrium chloride, lanthanum chloride, scandium chloride, MgSiF 6 , CaSiF 6 , BaSiF 6 , SrSiF 6 , or a combination thereof.
4. The process according to claim 1 , wherein the second solution additionally comprises an organic solvent selected from the group consisting of methanol, ethanol, isopropyl alcohol, dimethylsulfoxide, acetonitrile, and combinations thereof.
5. The process according to claim 1 , wherein the second solution is free of an organic solvent.
6. The process according to claim 1 , wherein the first solution further comprises hydrofluoric acid.
7. The process according to claim 1 , wherein the precursor comprises magnesium.
8. The process according to claim 1 , further comprising contacting the phosphor of formula I in particulate form with a fluorine-containing oxidizing agentin gaseous form at an elevated temperature prior to combining the phosphor of formula I with the first solution.
9. The process according to claim 1 , wherein the phosphor of formula I is K 2 SiF 6 :Mn 4+ .
10. The process according to claim 1 , wherein
K 2 SiF 6 :Mn 4+ is combined in particulate form with a first solution comprising K 2 SiF 6 and hydrofluoric acid to form a suspension; and
a second solution is combined with the suspension, the second solution comprising a precursor selected from the group consisting of calcium chloride, strontium chloride, magnesium chloride, lanthanum chloride, yttrium chloride, scandium chloride, MgSiF 6 , CaSiF 6 , SrSiF 6 , BaSiF 6 , and combinations thereof.
11. A process comprising combining K 2 SiF 6 :Mn 4+ in particulate form in a first solution comprising K 2 SiF 6 and aqueous hydrofluoric acid, to form a suspension; and combining a second aqueous solution of a precursor of formula M′SiF 6 with the suspension, wherein M′ is Mg, Ca, Ba, Sr, or a combination thereof.
12. The process according to claim 11 , wherein the compound of formula M′ SiF 6 is MgSiF 6 .
13. A population of particles having a core comprising a phosphor of formula I and a manganese-free composite coating disposed on the core, the manganese-free composite coating comprising a compound of formula II and a metal fluoride selected from the group consisting of calcium fluoride, strontium fluoride, magnesium fluoride, yttrium fluoride, scandium fluoride, lanthanum fluoride, and combinations thereof,
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 an absolute value of a charge of the [MF y ] ion; and
y is 5, 6 or 7.
14. The population of particles according to claim 13 , wherein the phosphor of formula I is K 2 SiF 6 :M 4+ .
15. The population of particles according to claim 13 , wherein the compound of formula II is K 2 SiF 6 .
16. The population of particles according to claim 13 , wherein an amount of the manganese-free composite coating relative to the phosphor of formula I in the core ranges from 1-20%, wt/wt.
17. The population of particles according to claim 16 , wherein the amount of the manganese-free composite coating relative to the phosphor of formula I in the core ranges from 5-15%, wt/wt.
18. The population of particles according to claim 13 , wherein the phosphor of formula I is K 2 SiF 6 :M 4+ and the composite coating comprises K 2 SiF 6 and MgF 2 .
19. A lighting apparatus comprising a semiconductor light source and the population of particles in accordance with claim 12 .
20. A backlight device comprising the lighting apparatus according to claim 19 .
21. The backlight device according to claim 20 , wherein the backlight device is a television, computer monitor, mobile phones, conventional telephone, digital photo frame, tablet, laptop, automotive display, e-book reader, electronic dictionary or gaming device.