ELECTROPHORETIC DEPOSITION OF PHOSPHORS .2. DEPOSITION EXPERIMENTS AND ANALYSIS

A study of the electrophoretic deposition of ZnS:Ag (P-11) phosphor pa rticles from an isopropyl alcohol (IPA) bath containing magnesium nitr ate is discussed. The process was analyzed by studying the deposition of magnesium hydroxide, formed via electrolysis of water present in th e IPA, as well as the phosphor particles. A model was developed which predicts the deposition rates of both the hydroxide and phosphor, whic h agrees well with experimental results under conditions of varying ap plied voltages and deposition times. When the magnesium nitrate concen tration was varied, the model predicted the deposition rate of the hyd roxide, but failed to predict the low deposition rates of phosphor fou nd 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 r ates were explained by changes in zeta potential due to increased pH n ear the electrode surface and minimum amount of hydroxide required for adhesion of the particles. (C) 1994 Academic Press, Inc.