Uniform and continuous Y2O3 coating on ZnS phosphors

An investigation is reported of the coating of ZnS by Y2O3 using a sol–gel process. Yttrium isopropoxide was used as the precursor material and was dissolved in a toluene/isopropanol solution. The solution was refluxed at an elevated temperature before the phosphors were added. The coated phosphors were then fired in air to convert the hydroxide to oxide. Scanning electron microscopy confirmed the formation of coatings on ZnS powders. The coating morphology was strongly dependent on the sol–gel processing parameters and the range of solution concentration and pH values necessary to form continuous coatings were determined. The cathodoluminescence properties of the coated phosphors were also investigated and an improvement in phosphor maintenance was observed.