Uniform and continuous SiO2 coating on ZnS phosphor

An investigation is reported for the coating of ZnS particles by silica using a buffer solution. Sodium silicate was used as the precursor material and it was diluted in water. The coating was performed at room temperature and sodium silicate was added drop-wise in the continuously stirred suspension of ZnS in the buffer solution. Coated phosphors were then fired in air to form a continuous dehydrated film. SEM (scanning electron microscopy), EDAX (energy dispersive X-ray) and XRD (X-ray diffraction) were used to characterize the coating. The coating morphology was strongly dependant on the sodium silicate concentration and temperature and pH of the buffer solution. The coated phosphor was found to be stable in AgNO3 solution and the decrease of PL (photoluminescence) property was minimum after coating.