Preparation of transparent nanocrystal phosphors and their application for wavelength conversion optical devices

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Chemically and thermally stable LaPO_4 doped with Ce^<3+> and Tb^<3+> exhibits green emission corresponding to the f-f transition of Tb^<3+> through energy transfer from Ce^<3+> to Tb^<3+> during exciting the d-f transition of Ce^<3+>. We discuss the influence of solvents and surface modifiers of the transparent LaPO_4 : Ce, Tb colloidal solutions on their crystal fields and photoluminescence properties. The transparent LaPO_4 : Ce, Tb colloidal solution was prepared from acetates and trimethyl phosphate in the mixed solvent of water and methanol by autoclave treatment below 150℃, followed by dialysis. According to the observation by transmission electron microscope and the particle size measurement by dynamic light scattering, the particles were less than 10nm in diameter. We found out the method for preparing transparent colloidal solutions of LaPO_4 : Ce, Tb with surface modification, e.g., by the addition of sodium polyphosphate, lauryl phosphate and hydrophilic phosphate modifiers, or by redispersing modified nanoparticles in n-hexane and dimethyl sulfoxide. We verified surface passivation, i.e., capping surface anion vacancies by surface modification based on the quantitative analysis of photoluminescence internal quantum efficiency and the decay curve measurement. On the other hand, we attempted to produce nanoparticle-dispersed resin sheets from the colloidal solution of 〜5nm ZnS : Mn nanoparticles. We also investigated other phosphors with different luminescence colors and the same excitation region as that of ZnS : Mn.