텅스텐산 란타넘 형광체의 합성 및 분광학 특성

Abstract

Synthesis and Spectroscopic Properties of Lanthanum Tungstate Phosphors Cheol Woo Park

Department of Physics, The Graduate School, Pukyong National University

Abstract The phosphors La2W3O12 and La6W2O15 doped with Eu3+ and Dy3+ ions were prepared by solid state reaction method. The phase formations of the phosphors were confirmed by the X-ray diffraction. Excitation and emission spectra together with time-resolved spectra were obtained in the temperature region 15 – 300 K. Doping of La2W3O12 by Eu3+ and Dy3+ ions gives rise to no impurity phase up to the concentration of 15 mol% in the lattices. When the doping concentration of Dy3+ increases over 80 mol% the phase transforms from La2W3O12 to Dy2W3O12 in the La2-xDyxW3O12 phosphors. The strong excitation bands due to the ligand to metal ion charge transfer (CT) transition of WO4 and O2- - Eu3+ CT transition are observed in the UV region for Eu3+-doped La2W3O12 and La6W2O15 phosphors. The excitation into the CT state causes the strong red emission at 615 nm due to the 5D0 → 7F2 transition. In Dy-doped La2W3O12 shows strong emissions due to the 4F9/2 → 6H13/2 transition at 576 nm with somewhat weaker emission at 482 nm due to the 4F9/2 → 6H15/2 transition. The emission are also observed in the infrared region 800-1200 nm due to the transitions from the 4F9/2 level to the 6F5/2 (835 nm), 6F7/2 (925 nm), 6H5/2 (1002 nm), 6F9/2 (1174 nm) levels. The emission under excitation of the WO4 band is observed at around 500 nm with bandwidth of about 150 nm at 15 K for Dy, Eu-undoped phosphors. The WO4 emission is quenched rapidly from 150 K and becomes much weaker at room temperature. The same result is obtained for decay times of the WO4 emission as a function of temperature in which the decay time becomes shorter by the quenching effect. The WO4 emission intensity is significantly reduced by doping with Dy3+ and Eu3+ ions indicating that efficient energy transfers occurs from the WO4 excitation state to the Eu3+ and Dy3+.