ELECTROPHORETIC DEPOSITION OF PHOSPHORS .2. DEPOSITION EXPERIMENTS AND ANALYSIS

A study of the electrophoretic deposition of ZnS:Ag (P-11) phosphor particles from an isopropyl alcohol (IPA) bath containing magnesium nitrate is discussed. The process was analyzed by studying the deposition of magnesium hydroxide, formed via electrolysis of water present in the IPA, as well as the phosphor particles. A model was developed which predicts the deposition rates of both the hydroxide and phosphor, which agrees well with experimental results under conditions of varying applied voltages and deposition times. When the magnesium nitrate concentration was varied, the model predicted the deposition rate of the hydroxide, but failed to predict the low deposition rates of phosphor found experimentally at magnesium nitrate concentrations of 10(-5) and 10(-4) M. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was unable to account for the low deposition rates. The low phosphor deposition rates were explained by changes in zeta potential due to increased pH near the electrode surface and minimum amount of hydroxide required for adhesion of the particles. (C) 1994 Academic Press, Inc.