Processes for preparing color stable Mn4+ doped phosphors include contacting a phosphor of formula I with a fluorine-containing oxidizing agent in gaseous form at temperature ≦225° C. to form the color stable Mn4+ doped phosphor A x ⁢ MF y ⁢ : ⁢ Mn 4 + I wherein A is independently at each occurrence Li, Na, K, Rb, Cs, 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; x is the absolute value of the charge of the MFy ion; and y is 5, 6 or 7. In another aspect, the processes include contacting a phosphor of formula I at an elevated temperature with an oxidizing agent comprising a C1-C4 fluorocarbon, to form the color stable Mn4+ doped phosphor.