Surface Passivation toward Highly Stable Mn 4+ ‐Activated Red‐Emitting Fluoride Phosphors and Enhanced Photostability for White LEDs

Mn 4+ ‐activated red‐emitting fluoride phosphors are indispensable candidates for white light emitting diodes (WLEDs) with enhanced color rendition, however, their intrinsic hydrolysis characteristics seriously restricted the durability applications. Here, a facile and general postsynthetic hydrogen peroxide (H 2 O 2 ) surface passivation strategy is proposed to treat the K 2 XF 6 :Mn 4+ (KXF, X = Ti, Si, Ge) phosphors, in which a Mn 4+ ‐rare surface protective layer appears and further covers the corresponding particles. The environment moisture can be effectively isolated by the Mn 4+ ‐rare surface passivation layer with low solubility, which will be sacrificed to protect the phosphor particles even if under extreme hydrolysis conditions. The relative external quantum efficiency of the optimized phosphors still maintains over 96% after the passivation treatment, and the relative luminous intensity still remain 97% even when soaked in water after 12 h. The correlated color temperature of high‐power WLEDs fabricated by the passivated phosphors has no remarkable change during aging process (100 days) in the high temperature (85 °C) and high humidity atmosphere (85%). It is expected that such a surface‐redox strategy can be expanded to other doped materials systems, and also opening a new perspective for the development of luminescence materials with enhanced surface stability and device duration.