이터븀 기반 몰리브덴산염계 결정에 도핑된 희토류 이온의 형광 및 상방전환 특성 연구

Abstract

The phosphors of KLn(MoO4)2 (Ln = Gd, Yb) doped with Eu3+, Tb3+, Tm3+ ions were prepared by solid state reaction method. The luminescence properties of the samples are investigated by optical and laser-excitation spectroscopy based on the analysis of the excitation, emission and upconversion spectra. Substitution of Eu3+ for Yb3+ changes the host structure from orthorhombic KGd(MoO4)2 to triclinic KEu(MoO4)2 in KGd1-XEux(MoO4)2. Tm3+ - doped KYb(MoO4)2 lattices form solid solution up to the concentration of 100 mol%. Doping of KGd1-x-yYbxTmy(MoO4)2 by Yb3+ ions gives rise to single phase up to the concentration of 10 mol% in the lattices. When the doping concentration of Yb3+ increases over 30 mol% the phase transforms from KGd(MoO4)2 to KYb(MoO4)2 in the KGd1-x-yYbxTmy(MoO4)2. The excitation spectra for monitoring the 5D0 – 7F2 emission of Eu3+ show broad Mo6+ - O2- CT bands with maxima centered around 220 nm and band edges at around 360 nm. The sharp peaks from 360 nm to 500 nm are ascribed to the intra-configurational 4f – 4f transitions of Eu3+ in the host lattices. The optical absorption bands due to the self-trapped exciton transition of the (MoO4)2- group are observed in the excitation spectra obtained by monitoring Tb3+ emission suggesting that the energy transfer occurs from (MoO4)2- groups to Tb3+ in the KGd1-xTbx(MoO4)2. The upconversion emissions of the KYb1-xTmx(MoO4)2 and KGd1-xYbxTm0.001(MoO4)2 samples are investigated in the wavelength range 400 ~ 850 nm under excitation at 975 nm. The 475 nm blue, 651 nm and 685 nm red emissions are observed and those relative intensities depend strongly on Yb3+ concentration. The upconversion processes are discussed in relation to energy transfer and energy diffusion among Yb3+ and Tm3+ ions.