The paper presents a novel cation exchange strategy for synthesizing Mn4+-activated fluoride microcrystals, such as K2TiF6, K2SiF6, NaGdF4, and NaYF4, which are emerging as non-rare-earth red phosphors for high-efficacy warm white LEDs. The method involves mixing the fluoride host with a small volume of HF solution containing Mn4+ ions, followed by heating to dryness. This approach allows for the efficient synthesis of high photoluminescence quantum yield (PL QY) Mn4+-activated fluoride phosphors, with K2TiF6:Mn4+ achieving a PL QY of up to 98%. The red phosphor is then used to fabricate warm white LEDs with low correlated color temperature (CCT), high color rendering index (CRI), and luminous efficacy. The study demonstrates the potential of K2TiF6:Mn4+ as a commercial red phosphor in warm white LEDs and opens new avenues for exploring novel non-rare-earth red emitting phosphors.The paper presents a novel cation exchange strategy for synthesizing Mn4+-activated fluoride microcrystals, such as K2TiF6, K2SiF6, NaGdF4, and NaYF4, which are emerging as non-rare-earth red phosphors for high-efficacy warm white LEDs. The method involves mixing the fluoride host with a small volume of HF solution containing Mn4+ ions, followed by heating to dryness. This approach allows for the efficient synthesis of high photoluminescence quantum yield (PL QY) Mn4+-activated fluoride phosphors, with K2TiF6:Mn4+ achieving a PL QY of up to 98%. The red phosphor is then used to fabricate warm white LEDs with low correlated color temperature (CCT), high color rendering index (CRI), and luminous efficacy. The study demonstrates the potential of K2TiF6:Mn4+ as a commercial red phosphor in warm white LEDs and opens new avenues for exploring novel non-rare-earth red emitting phosphors.