Adhesion of colloidal SiO2 particles on ZnS-type phosphor surfaces

The interaction between colloidal SiO2 particles and the surface of ZnS-typ e phosphors has been studied. The green emitting phosphor ZnS:Cu,Al,Au appl ied in color television tubes was chosen as a model compound. After the sur face 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 coll oidal ZnO particles (d(50) = 81 nm), colloidal SiO2 particles (d(50) = 207 nm) were added. Thereafter, the amount of adhered SiO2 was investigated bas ed 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 particl es adhere sufficiently only if ZnO is present on the ZnS surface. The SiO2 particles are located on top of the ZnO. Finally, the attractive interactio ns in the system ZnS-ZnO-SiO2 are discussed in more detail. (C) 2000 Academ ic Press.