US Patent 8252613 Color stable manganese-doped phosphors

A process for preparing color stable Mn+4 doped phosphors includes providing a phosphor of formula I;Ax[MFy]:Mn+4  Iand contacting the phosphor in particulate form with a saturated solution of a composition of formula II in aqueous hydrofluoric acid;Ax[MFy];  IIwhereinA is Li, Na, K, Rb, Cs, NR4 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 [MFy] ion; andy is 5, 6 or 7.In particular embodiments, M is Si, Ge, Sn, Ti, Zr, or a combination thereof.