Moisture-Resistant Mn4+ -Doped Core-Shell-Structured Fluoride Red Phosphor Exhibiting High Luminous Efficacy for Warm White Light-Emitting Diodes.

K2 TiF6 :Mn4+ is a highly efficient narrow-band emission red phosphor with promising applications in white light-emitting diodes (LEDs) and wide-gamut displays. Nevertheless, the poor moisture-resistant properties of this material hinder commercialization. A convenient reverse cation-exchange strategy is introduced for constructing a core-shell-structured K2 TiF6 :Mn4+ @K2 TiF6 phosphor. The outer K2 TiF6 shell acts as a shield for preventing moisture in the air from hydrolyzing the internal MnF6 2- group, while effectively cutting off the path of energy migration to surface defects, thereby increasing the emission efficiency (especially for the phosphors doped with high concentrations of Mn4+ ). Employed as a red phosphor, the packaged white LED exhibits an extraordinarily high luminous efficacy of 162 lm W-1 , a correlated color temperature (CCT) of 3510 K, and a color rendering index of 93 (Ra ). Aging tests performed on this device at 85 °C and 85 % humidity for 480 h retain up to 89 % luminous efficacy. The findings could facilitate commercial application of K2 TiF6 :Mn4+ @K2 TiF6 phosphor.