Preparation of Y₂O₃:Yb,Er Infrared-to-Visible Conversion Phosphor Fine Particles Using an Emulsion Liquid Membrane System

Upconverting phosphor fine particles (Y 2 O 3:Yb,Er) have been prepared, using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as the surfactant and VA-10 (2-methyl-2-ethylheptanoic acid), DTMBPA (bis(1,1,3,3-tetramethylbutyl)phosphinic acid), or Cyanex272 (bis(2,4,4-trimethylpenthyl)phosphinic acid) as the extractant (cation carrier). The Y, Yb, and Er ions were extracted, from the external water phase, and stripped into the internal water phase, to make precursor composite oxalate particles. The precursor particles obtained in the VA-10 system were mainly 20−60 nm in size, together with a smaller amount of submicron-sized spherical particle, and were much smaller than those prepared in homogeneous aqueous solution (1−10 μm in size). The molar composition of the particles, {M/(Y+Yb+Er)} p (M = Yb or Er), prepared in the VA-10 and DTMBPA systems, was almost proportional to that of the feed external solution, {M/(Y+Yb+Er)} f . Calcination of the composite Y−Yb−Er oxalate particles obtained in the VA-10 system produced Y 2 O 3:Yb,Er particles about 50 nm in size. The aggregation of the oxide primary particles was found to be suppressed by increasing the surfactant concentration in the VA-10 system. The Y 2 O 3:Yb,Er particles demonstrated an upconversion emission at 662 nm, by infrared excitation (λ ex = 960 nm). At an external feed aqueous solution of {Yb/(Y+Yb+Er)} f = 0.08, {Er/(Y+Yb+Er)} f = 0.01, the 662 nm emission peak intensity reached a maximum value. The present upconverting phosphor fine particles, about 50 nm in diameter, may be applied to the reporters in immunoassays or DNA assays.