Preparation of Sr2CeO4 Blue Phosphor Particles and Rare Earth (Eu, Ho, Tm, or Er)-Doped Sr2CeO4 Phosphor Particles, Using an Emulsion Liquid Membrane System

Sr 2 CeO 4 blue phosphor particles were prepared with an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, which could be utilized as a microreactor for the preparation of size- and morphology-controlled fine particles. In the ELM system, Sr 2+ and Ce 3+ ions were extracted from the external water phase by extractant (cation carrier, bis(2-ethylhexyl)phosphoric acid) and were stripped into the internal water phase, containing oxalic acid solution, to form the submicrometer-sized composite Sr−Ce oxalate particles, which were much smaller than those obtained in a homogeneous aqueous solution. Calcination of the precursor oxalate particles obtained in the ELM system produced submicrometer-sized Sr 2 CeO 4 particles, which showed a charge-transfer (CT) emission at 467 nm (λ ex = 254 nm). The photoluminescence properties of rare earth-doped Sr 2 CeO 4 (Sr 2 CeO 4:Ln 3+; Ln = Eu, Ho, Tm, or Er) were also investigated, and the characteristic emissions corresponding to doped rare earth ions, effected by energy transfer from the triplet excited state of MLCT (metal-to-ligand charge transfer) state for Sr 2 CeO 4 (sensitizer) to the rare earth ions (activators), were observed.