Adhesion of colloidal ZnO particles on ZnS-type phosphor surfaces

Chemical and physical aspects of the adhesion of colloidal ZnO particles (d(50) = 81 nm) on the surface of ZnS-type phosphors have been studied. Here, the green-emitting phosphor ZnS:Cu,Al,Cu (d(50) = 5-0 mu m) applied in TV screens was chosen as model compound. The ZnS material was pretreated in various ways (H2O, HCl, H2O2) and reacted thereafter with a suspension containing colloidal ZnO particles. Analytical investigations (SEM, ESCA) have shown that the adhesion of colloidal ZnO particles is strongly affected by the degree of hydrolysis of the ZnS surface. Electroacoustic investigations (ESA) prove that both types of surfaces, hydrolyzed ZnS as well as colloidal ZnO, are positively charged. Even so, adhesion of ZnO particles is encouraged very much under these conditions, indicating that secondary attractive forces (electrostatic interaction, chemical bonding) determine the amount of colloidal ZnO adhered on a ZnS-type phosphor. (C) 2000 Academic Press.