A process for synthesizing a Mn4+ doped phosphor includes contacting a precursor of formula I, at an elevated temperature with a fluorine-containing oxidizing agent in gaseous form to form the color stable Mn4+ doped phosphor; 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 the absolute value of the charge of the [MFy] ion; y is 5, 6 or 7; and amount of Mn ranges from about 0.9 wt % to about 4 wt %, based on total weight.