Red K₂LiGaF₆:Mn⁴⁺ phosphors have been synthesized by the facile cation-exchange method. To optimize the optical properties, the phosphors were synthesized by using different reaction conditions. The highest luminescence intensity was increased 3.6 times for the Mn concentration of 1%, reaction temperature of 20 °C, and reaction time of 1 h. Replacement of the trivalent Al by Ga resulted in K₂LiGaF₆:Mn⁴⁺ having better photoluminescence properties than K₂LiAlF₆:Mn⁴⁺. Furthermore, the studies of the temperature-dependent emission intensity of the phosphors confirmed their good thermal stability, making them promising red phosphor candidates for white light-emitting diodes.