Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

Mn⁴⁺-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 Mn⁴⁺-activated fluoride microcrystals such as K₂ TiF⁶, K² SiF⁶, NaGdF⁴ and NaYF⁴. Particularly we achieve a photoluminescence quantum yield as high as 98% for K₂ TiF₆:Mn⁴⁺. 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 (R _a=81) and luminous efficacy of 116 lm w^-1. These findings show great promise of K₂ TiF₆:Mn⁴⁺ 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.