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

Abstract K 2 TiF 6 :Mn 4+ 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 K 2 TiF 6 :Mn 4+ @K 2 TiF 6 phosphor. The outer K 2 TiF 6 shell acts as a shield for preventing moisture in the air from hydrolyzing the internal MnF 6 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 Mn 4+ ). 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 (R a ). 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 K 2 TiF 6 :Mn 4+ @K 2 TiF 6 phosphor.