Improved moisture resistance of SrS:Eu2+ phosphors with nanoscale SiO2 coating

Orange-emitting SrS:Eu2+ phosphors were coated with nanoscale SiO2 and their photoluminescence (PL) degradation behavior in moist air was investigated. The SiO2 coating was obtained by sol-gel process using diethoxydimethylsilane (DEDMS) and the coating content was varied from 0.5 to 2 wt%. The coatings were composed of a uniform, continuous, and amorphous SiO2 layer of 30-50 nm thickness and the coating thickness was not varied significantly with the coating content. No peak shift and no decrease of PL intensity were observed after coating. The PL intensity of the coated phosphors decreased to ∼75% of the original value after 10 h exposure to moist air, while the uncoated phosphor decreased to ∼33%, which indicates the improved moisture resistance of the nanoscale SiO2 coated SrS:Eu2+ phosphors.