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. K 2 SiF 6 :Mn 4+ particles were prepared by co‐precipitation and then coated by esterification of P 2 O 5 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 high‐temperature (85 °C) conditions for one month. Warm white‐light‐emitting diodes that consisted of blue InGaN chips, the prepared K 2 SiF 6 :Mn 4+ phosphors, and either yellow Y 3 Al 5 O 12 :Ce 3+ phosphors or green β‐SiAlON: Eu 2+ phosphors showed excellent color rendition.