Preparation of Sr2CeO4 blue phosphor particles and rare earth (Eu, Ho, Tm, or Er)-doped Sr2CeO4 phosphor particles, using an emulsion liquid membrane system

Sr2CeO4 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, Sr2+ and Ce3+ 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 Sr2CeO4 particles, which showed a charge-transfer (CT) emission at 467 nm (lambda(ex) = 254 nm). The photoluminescence properties of rare earth-doped Sr2CeO4 (Sr2CeO4: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 Sr2CeO4 (sensitizer) to the rare earth ions (activators), were observed.