Preparation of Y₂SiO₅:Ln³⁺ (Ln = Eu, Tb, Sm) and Gd_9.33(SiO₄)₆O₂:Ln³⁺ (Ln = Eu, Tb) Phosphor Fine Particles Using an Emulsion Liquid Membrane System

Abstract

Y2SiO5:Eu3+ and Gd9.33(SiO4)6O2:Eu3+ red phosphor particles were prepared using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, which could be utilized as a microreactor for precipitation reaction of rare earth oxalate and hydrolysis−condensation reaction of Si alkoxide, to obtain size- and morphology-controlled precursor particles. Y3+ (or Gd3+) and Eu3+ ions were extracted from the external water phase of the ELM system by extractant (cation carrier, 2-methyl-2-ethylheptanoic acid) and were stripped into the internal water phase, consisting of oxalic acid and tetramethyl orthosilicate (TMOS) as the Si source, to make composite Y−Eu−Si (or Gd−Eu−Si) oxalate particles. The precursor particles were 20−60 nm in size, containing small amounts of flat particles of 300 nm in size. By calcination of the precursor oxalate particles obtained in the ELM system, submicrometer-sized X1-phase Y2SiO5:Eu3+ (or Gd9.33(SiO4)6O2:Eu3+) particles were produced, which were smaller than those prepared by the conventional sol−gel method. The resulting phosphor particles demonstrated a photoluminescence around 600 nm (λex= 254 nm). Photoluminescence properties of Tb3+- or Sm3+-doped Y2SiO5 and Gd9.33(SiO4)6O2:Tb3+ particles were also investigated, and the characteristic photoluminescence corresponding to doped rare earth ions was observed.