CATAPHORETIC DEPOSITION OF PHOSPHOR

In a fundamental study of the cataphoretic deposition of phosphor from an isopropanol (IPA) solution, the electrophoretic properties of the phosphor particles, the dissociation of magnesium and lanthanum nitrate salts in IPA, and the reactions of Mg2+ and La3+ were investigated. It was determined that Mg2+ and La3+ near the cathode react to form an adhesive hydroxide matrix which binds the phosphor particles to the substrate. The degree of dissociation of the nitrate salts in IPA determined from conductivity measurements is less than a few percent. The conductivity of the plating bath increases with successive depositions due to the absorption of water from air by IPA, which also increases the ionization of the nitrate salts. From zeta potential measurements, the phosphor itself is negatively charged and only an extremely small concentration of ions is required to charge the particles positively in the bath. Using the zeta potential measurements to calculate electrophoretic velocity, a model to predict the deposition rate of phosphor was developed and was found to be in good agreement with experimental results when the settling of the phosphor was taken into account. © 1990, The Electrochemical Society, Inc. All rights reserved.