We have developed a method to coat the phosphors comprising of multi-component systems 10 prevent them aging effect. Y2O3 was selected as a protective material because of its superior ability to resist against mercury adsorption and oxidation and its good UV transparency at the wavelength used for phosphor activation. By dispersing the phosphor particles in the polyol medium that contains the yttrium precursor, heterogenous nucleation and growth on the particle surface were induced. This allows us to obtain a thick and uniform coating of the phosphors with amorphous Y2O3 sols. The heat-treatment condition for Y2O3 sols was carefully controlled to keep the phosphors from surface oxidation and at the same time to assume the complete crystallization and burn-out of organic impurity by XRD and TG/DTA. The surface morphology of the coated phosphors was examined by SEM as a function of reaction time and temperature and precursor concentration. (c) 2005 Elsevier Inc. All rights reserved.