Sodium gadolinium tungstate NaGd(WO₄)₂: Growth, crystallography, and some physical properties

Pure, and Nd³⁺-doped NaGd(WO₄)₂ (NGW) single crystals, up to ∼85 mm long and ∼30 mm in diameter, have been grown using the Czochralski method. The Nd³⁺ segregation coefficient for growth along the [1 0 0] direction was 1.3±0.025. X-ray diffraction at room temperature established the lattice constants as: a=5.2483(2) Å and c=11.392(2) Å, for the tetragonal scheelite-like structure (space group I4₁/a), with two formula units in the unit cell. Inter-atomic distances and bond angles are also given. The thermal expansion coefficients were α_a=11.6×10^-6 /°C and α_c=23.3×10^-6 /°C, in the a and c directions, respectively. The Nd³⁺ absorption spectrum at around 800 nm for E⊥c polarization was measured with high resolution, providing a peak absorption cross-section of 2.6×10^-20 cm² at 800.8 nm.