Coating of ZnS phosphor by $SiO_2$ sol-gel

Silica coating on ZnS particles with buffer solution has been investigated. Diluted sodium silicate in water was used as the precursor material and it was diluted in water. Sodium silicate was added drop-wise in the continuously stirred suspension of ZnS in the buffer solution at room temperature. Smooth and evenly distributed silica coated ZnS phosphors has been obtained when the pH of buffer solution was 10, the concentration of sodium silicate in water was 20 wt%, firing temperature was 500 $^{\circ}C$.