The interaction between colloidal SiO2 particles and the surface of ZnS-type phosphors has been studied. The green emitting phosphor ZnS:Cu,Al,Au applied in color television tubes was chosen as a model compound. After the surface of the phosphor particles (d(50) = 5.0 mu m) was treated in different manners like washing with H2O, HCl, or H2O2 as well as precoating with colloidal ZnO particles (d(50) = 81 nm), colloidal SiO2 particles (d(50) = 207 nm) were added. Thereafter, the amount of adhered SiO2 was investigated based on SEM and ESCA analysis. By ESA measurements the surface charge of the colloids and the differently treated ZnS materials was investigated. Based on the experimental results it can be concluded that colloidal SiO2 particles adhere sufficiently only if ZnO is present on the ZnS surface. The SiO2 particles are located on top of the ZnO. Finally, the attractive interactions in the system ZnS-ZnO-SiO2 are discussed in more detail.