Crystal Structure of Scheelite-type LiTb(WO_4)_2 and Multi-color Emitting Properties Doped by Eu~(3+)

Single crystal of lithium terbium tungstate LiTb(WO4)2 has been grown by the flux method. The crystal structure was refined from single-crystal X-ray data. It crystallizes in tetragonal system, space group I41/a with a = 5.1749(9), c = 11.1953(19) ?, V = 299.81(12) ?~3, Z = 2, Mr = 661.56, Dc = 7.328 g/cm^3, F(000) = 560, μ(MoKα) = 49.94 mm^-1, R(F^2 > 2σ(F^2)) = 0.026 and wR(F^2) = 0.070. It features a typical scheelite-type structure composed of two-direction packing of isolated WO4 tetrahedra. Li and Tb atoms in the structure occupy the same crystallographic site. Moreover, a series of solid solution phosphors LiTb(1-x)Eux(WO4)2(x = 0.004~0.1) were synthesized by high temperature solid-state reactions. The phosphors could be effectively excited by a wavelength range from 379 to 487 nm, which matches well with the UV and near-UV LED chip. The emission color of the phosphor can be tuned from green, through yellow to red by simply adjusting the relative Eu³⁺ and Tb³⁺ concentration due to the Tb³⁺ to Eu³⁺ energy transfer.