Study on the stability of phosphor SrAl2O4:Eu2+, Dy3+ in water and method to improve its moisture resistance

Phosphor SrAl2O4:Eu2+, Dy3+ with persistent green luminescence is chemically unstable to water or moisture. Its hydrolysis process was detailed studied through a series of experiments, and the products of hydrolysis were also analyzed intensively. Changes of pH value of suspensions, the structures and optical properties of the hydrolysis products had been studied. A layer of moisture barrier was also applied to the phosphor particles by heating phosphor particles and ammonium difluoride (NH4HF2) at an elevated temperature, which formed alkaline earth fluoride moisture-resistance coating on phosphor surfaces. Scanning electron microscopy and X-ray diffraction patterns were employed to characterize the coatings. Changes of photoluminescence intensity and the pH values of phosphor solution were measured to characterize the stability of phosphor. All results indicated that alkaline earth fluorides were effective moisture-imperious coating for strontium aluminates phosphors.