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 °C was approximately 416 % of the initial value at 25 °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.