SrSO4:Sm3+ phosphors obtained by precipitation method are coated with SiO2 and their photoluminescence (PL) degradation behavior is investigated. The SiO2 coating is obtained by the ultrasonic sonochemical process using tetraethylorthosilicate (TEOS) as silicon coating reagent and the coating content is varied from 0.5 to 2 wt%. Powder X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), fluorescence spectrometer, and Fourier transform infrared spectrometer are employed to characterize the coating. Moisture resistances of coated SrSO4:Sm3+ phosphors have been enhanced to a great degree without more loss of their optical properties based on the existence of the SiO2 thin layer. The PL intensity of the coated phosphors decreases to similar to 83% of the original value after 38 h soaking the phosphors in deionized water, while the uncoated phosphor decreases to similar to 40%. (C) 2012 Elsevier B.V. All rights reserved.