Structure dependence of near-infrared stimulated blue emission in polycrystalline Ln2(WO4)3 (Ln = Gd and Lu) doped with Tm and Yb

Tm- and Yb-doped gadolinium tungstate, (GdxTmyYb1-x-y)(2)(WO4)(3) (x = 0.7-0.9; y = 0.001-0.01), have been prepared by the polymerized complex method to achieve a homogeneous dispersion of dopants and to stabilize the host structure. Decomposition (900 degrees C 5 h) of the precursors with x = 0.8-0.9 yielded a pure monoclinic phase, while that of x = 0.7 resulted in formation of an orthorhombic 3 impurity. The monoclinic phase exhibits bright up-converted blue emission due to the (1)G(4) -> H-3(6) transition of Tm3+ (472 nm) upon excitation into the Yb3+:F-2(7/2) -> F-2(5/2) absorption band as a result of energy transfer from Yb to Tm. The orthorhombic impurity acts as a strong quencher of emission, and the quenching mechanism has been discussed on the basis of structural and spectroscopic properties of orthorhombic Lu-2(WO4)(3):Tm,Yb prepared by the same method. (C) 2009 Elsevier B.V. All rights reserved.