PREPARATION AND CHARACTERIZATION OF ZINC-SULFIDE PHOSPHORS COATED WITH BARIUM-TITANATE USING SOL-GEL METHOD

A study has been carried out to prepare BaTiO3-coated ZnS phosphors utilizing a sol-gel technique with mixed solutions of titanium alkoxides and barium alkoxides and acetate in various solvents. The precursor gel of BaTiO3 prepared by the hydrolysis of iso-propoxides of barium and titanium in iso-propylalcohol transformed to crystalline BaTiO3 at a low temperature of 550 degrees C. Coating was carried out by heating the BaTiO3 precursor gel containing ZnS phosphors in air at 450 degrees C for 5 h, followed by heating in nitrogen-flowing atmosphere at 570 degrees C for 10 h in order to prevent ZnS phosphors from being oxidized. However, the heat-treatment in nitrogen flowing atmosphere depressed the electroluminescent intensity because of oxygen defects in BaTiO3. It was found that annealing in air at 40O degrees C for 5 h gives rise to the brightest phosphors.