Y 2 O 2 S:Eu Red Phosphor Powders Coated with Silica

Y 2 O 2 S:Eu red phosphor powders were coated with silica (SiO 2 ), using sol–gel and heterocoagulation techniques. Phosphor powders were dispersed in ethanol with tetraethyl orthosilicate and water. Hydrochloric acid was used to catalyze the sol–gel reaction, and an amorphous film 10–20 nm thick was observed via transmission electron microscopy (TEM). Colloidal SiO 2 powders 10–70 nm in size were used, and the SiO 2 powder coating was made by controlling pH values in the range of 4.5–8, in which a negatively charged surface of SiO 2 powder and a positively charged surface of red phosphor powder were formed. Then, SiO 2 powders were adsorbed electrically onto the phosphor powder surface, as evidenced by TEM, dissolution, and zeta potential measurements. Chemical bonding in the coating was studied using electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy.