Thin SiO2 coating on ZnS phosphors for improved low-voltage cathodoluminescence properties

A significant improvement (40-60%) was reported in the low voltage (100-1000V) cathodoluminescence efficiency of ZnS phosphors coated with SiO2 by the sol-gel technique. The properties of the coatings were found to be critically dependent upon the precursor concentration, pH value and the temperature of the solution with optimum performance being obtained for a SiO2 concentration of 1.0 wt%, pH values between 7-9, and a solution temperature of 83 degreesC, The efficiency curves exhibited a characteristic voltage dependence which was analyzed by a one-dimensional numerical model. Enhanced low voltage efficiency was attributed to a reduction of surface recombination and the actual shape of the efficiency curve was determined by the interplay between the reduction of surface recombination and energy losses in the SiO2 coating.