Luminescent characteristics and morphology of Eu3+:YVO4 phosphor powders prepared by HCR and flux techniques

The emission intensities of Eu3+:YVO4 red phosphors depend significantly on the morphology and Y-V-O stoichiometry of powder particles. The low-temperature hydrolyzed colloid reaction (HCR) technique with different firing regimes in air and crystallization from lithium metavanadate (LiVO3) flux with subsequent grinding have been investigated. Powders reacted at the quasi-congruent (49.3 mol% V2O5-50.7 mol% Y2O3) composition and fired at temperatures up to 1200 degrees C exhibited higher emission intensities than the powders weighed at the stoichiometric (50 mol% V2O5-50 mol% Y2O3) ratio. After higher temperature (1400, 1600 degrees C) treatments the stoichiometric composition produces better luminescent properties approaching that of the highly optimized industrial powder standard (Sylvania 2391). Only limited emission was obtained for the crystalline powder prepared from LiVO3 flux due to the influence of mechanical grinding. Powder morphology and crystal structure were investigated by high-resolution transmission electron microscopy (TEM). The small particles produced al low temperature are surprisingly well crystallized with well resolved lattice images. The small particles contain internal surfaces as well as large external surfaces which contribute to the degradation of phosphor properties.