In Situ Formation of Ultrathin Composite Shell with Strong Water Resistance on the Surface of K₂SiF₆:Mn⁴⁺ via NaClO Treatment

Abstract Solving the problem of poor weather resistance of Mn⁴⁺‐doped fluoride phosphors is pivotal for their application in white‐light‐emitting diodes (WLEDs). This study introduces a one‐step synthesis strategy for the phosphor T‐KSF:Mn (KSF:M = K₂SiF₆:Mn⁴⁺ and T = surface‐treated with NaClO) that involves the use of a NaClO solution as a treatment agent to augment the water resistance of this phosphor. The results of transmission electron microscopy, electron diffraction tomography, and X‐ray photoelectron spectroscopy, analyses reveal the formation of an ultrathin composite shell (<5 nm) comprising K₂SiF₆ and KNaSiF₆ on the surface of T‐KSF:Mn. The fluorescence intensity of the treated phosphor is 1.09 times that of the untreated phosphor, and its internal quantum efficiency reaches 82.72%. Even after 60 days of testing in a harsh hydrolysis environment, the fluorescence intensity of T‐KSF:Mn remains at 86.24%. At 150 and 200 °C, the integrated fluorescence intensity of T‐KSF:Mn surge to 256.84% and 292.29% of its initial value at 30 °C, respectively, demonstrating a substantial negative thermal quenching (NTQ) effect. Furthermore, the results of aging tests conducted at 85 °C and 85% relative humidity substantiate the effectiveness of the aforementioned strategy in considerably enhancing WLED stability under practical conditions.