Processes for preparing color stable red-emitting phosphors

A process for synthesizing a color stable Mn4+ doped phosphor, the process comprising contacting a phosphor of formula I,

• A
• x
• ⁢
• MF
• y
• ⁢
• :
• ⁢
• Mn
• 4
• +
• I
• at an elevated temperature with a fluorine-containing oxidizing agent to form the color stable Mn4+ doped phosphor, the fluorine-containing oxidizing agent comprises a compound selected from the group consisting of:
• F2, anhydrous HF, BrF5, NH4F, AlF3, SF6, SbF5, ClF3, KrF, XeF4, NF3, PbF2, ZnF2, SiF4, SnF2, CdF2, a C1-C4 fluorocarbon and a combination thereof;
• and
• contacting the color stable Mn4+ doped 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 independently at each occurrence Li, Na, K, Rb, Cs, NR4 or a combination thereof;
• M is independently at each occurrence Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;
• R is H, lower alkyl, or a combination thereof;
• x is independently at each occurrence the absolute value of the charge of the MFy ion;
• and
• y is independently at each occurrence 5, 6 or 7.