Uniform and continuous silica nanocoatings on ZnS phosphors

The penetration depth of the primary electrons into amorphous silica, anatase titania, Y(2)O(3), ZnO, In(2)O(3), indium and tin oxides is compared at lower voltages. It shows that amorphous silica has the largest penetration depth, thus the silica coatings will lead to minimal energy loss and maximal cathodoluminescence intensity. Almost uniform and continuous silica coatings on ZnS phosphors have successfully been obtained by a sol-gel method with the catalysis of ammonia. Zeta potential analysis shows that the ZnS phosphors are covered almost completely. An adsorption-catalysis-growth mechanism is suggested, and used to explain other ammonia-catalyzed coating processes.