Effects of NH3·H2O pretreatment on the fabrication of uniform titania nanocoating in an aqueous solution

An investigation is reported of the TiO2 nanocoating on the ZnS-based phosphor via a sol–gel method in an aqueous solution using titanium diethanolamine complex as the precursor. The pretreatment of ZnS phosphors with NH3·H2O is important to the coating process. When NH3·H2O was added into the ZnS phosphor suspension, OH− promoted the hydrolysis of Zn2+ on the surface of ZnS phosphors, which resulted in the formation of Zn–OH. Zn–OH reacted with the hydrolysis product of titanium diethanolamine complex, thus the titania coatings were obtained. The coating morphology was strongly dependant on the pH of the pretreated ZnS phosphor suspension and the weight ratio of ZnS to TiO2.