Application of chelation effect in improving the triple properties of K₂SiF₆Mn⁴⁺ phosphors through composite modification

Mn4+-doped fluoride phosphors are limited by their poor moisture resistance in practical applications of white light-emitting diodes (WLEDs). Herein, a new red light-emitting phosphor KSF:MnK2SiF6:Mn4+ was synthesized based on a novel strategy combining surface treatment with hexamethylene tetramine (HMTA) and coating with a matrix, hereafter referred to as P-KSF:Mn. Given the formation of the coordination bond between N and Mn4+ and the strong hydrogen bond between N and F in the shell after the protonation of HMTA, a dense and firm shell of rare Mn4+ formed on the sample surface. P-KSF:Mn showed strong emission, waterproof property and luminescent thermal stability, and its fluorescence intensity was 1.81 times that of KSF:Mn. After soaking in water for 90 d, the fluorescence intensity of P-KSF:Mn was 90.7 % of the initial value. The integrated fluorescence intensity at 200 degrees C was approximately 416 % of the initial value at 25 degrees C. The strong luminous thermal stability was supported by strong negative thermal quenching (NTQ), which is explained by the phonon induction mechanism. The WLED prototype assembled with P-KSF:Mn emitted warm white light with correlated color temperature (CCT) = 3112 K, color rendering index (CRI) = 90.7, and luminous efficiency (LE) = 119 lm/W. The results show that P-KSF:Mn is a potential candidate for applications in the field of warm WLEDs.