Highly water resistant surface coating by fluoride on long persistent Sr4Al14O25:Eu/Dy phosphor

A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600-700 °C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moisture-impervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.