Size- (submicrometer-sized) and morphology- (spherical) controlled composite Gd-Eu oxalate particles were prepared in an emulsion liquid membrane (water-in-oil-in-water emulsion) system. The oxalate particles thus prepared were calcined in air to obtain Gd2O3 : Eu3+ phosphor particles and in sulfur atmosphere to obtain Gd2O2S: Eu3+ phosphor particles. These submicrometer-sized spherical phosphor particles showed photoluminescence properties with emission peak at 614 nm for Gd2O3: Eu3+ and 628 nm for Gd2O2S: Eu3+.