Waterproof Alkyl Phosphate Coated Fluoride Phosphors for Optoelectronic Materials

A facile approach for coating red fluoride phosphors with a moisture-resistant alkyl phosphate layer with a thickness of 50-100 nm is reported. K₂SiF₆:Mn⁴⁺ particles were prepared by co-precipitation and then coated by esterification of P₂O₅ with alcohols (methanol, ethanol, and isopropanol). This route was adopted to encapsulate the prepared phosphors using transition-metal ions as cross-linkers between the alkyl phosphate moieties. The coated phosphor particles exhibited a high water tolerance and retained approximately 87% of their initial external quantum efficiency after aging under high-humidity (85%) and higherature (85°C) conditions for one month. Warm white-light-emitting diodes that consisted of blue InGaN chips, the prepared K₂SiF₆:Mn⁴⁺ phosphors, and either yellow Y₃Al₅O₁₂:Ce³⁺ phosphors or green β-SiAlON: Eu²⁺ phosphors showed excellent color rendition.