Uniform Y₂O₃ coating on multi-component phosphor powders by modified polyol process

We have developed a method to coat the phosphors comprising of multi-component systems to prevent them from 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, heterogeneous 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 assure 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.