Single crystal growth and luminescent properties of Tb doped GdTaO₄ by the μ-pulling down method

GdTaO₄ and (Gd_1-xTb_x)TaO₄ (x = 0, 0.001, 0.02, 0.04, 0.10, and 0.16) single crystals were grown by the micro-pulling down method. The crystallographic system of the grown crystals was identified to be monoclinic (I2/a), which is the stable low-temperature phase of GdTaO₄. In the photoluminescence (PL) spectra, intense emission was observed at 549 nm (⁵D₃→⁷F₄ transition of Tb³⁺) for every Tb doped GdTaO₄. In the excitation spectra for the 549 nm emission, several excitation paths to the Tb³⁺ were attributed: 4f-4f transitions of Gd³⁺, 4f⁸-4f⁷5d transitions of Tb³⁺ and charge transfer of TaO₄ ³⁻ group. Radiolumincece spectra under X-ray irradiation were taken, and the highest emission peak was observed at 544 nm, which was ascribed to the ⁵D₄→⁷F₅ transition of Tb³⁺. The Tb 2% doped GdTaO₄ showed the highest emission intensity at the 544 nm, and as increasing dopant concentration, the intensity decreased due to the cross-relaxation of Tb³⁺.