Mn(4+)-activated fluoride compounds, as an alternative to commercial (oxy)nitride phosphors, are emerging as a new class of non-rare-earth red phosphors for high-efficacy warm white LEDs. Currently, it remains a challenge to synthesize these phosphors with high photoluminescence quantum yields through a convenient chemical route. Herein we propose a general but convenient strategy based on efficient cation exchange reaction, which had been originally regarded only effective in synthesizing nano-sized materials before, for the synthesis of Mn(4+)-activated fluoride microcrystals such as K2TiF6, K2SiF6, NaGdF4 and NaYF4. Particularly we achieve a photoluminescence quantum yield as high as 98% for K2TiF6:Mn(4+). By employing it as red phosphor, we fabricate a high-performance white LED with low correlated colour temperature (3,556 K), high-colour-rendering index (Ra=81) and luminous efficacy of 116 lm W(-1). These findings show great promise of K2TiF6:Mn(4+) as a commercial red phosphor in warm white LEDs, and open up new avenues for the exploration of novel non-rare-earth red emitting phosphors.