Growth and spectral properties of Tm3+-doped NaGd(WO4)2 crystal

Thulium doped sodium gadolinium tungstate crystals with sizes of about 20 mm×45 mm were grown successfully by the Czochralski technique along the (001) orientation. X-ray powder diffraction (XRD) of sodium gadolinium tungstate was described and the linear thermal expansion coefficients for the c- and a-axes were measured as 1.60×10-5 and 7.89×10-6 °C-1. Polarized absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Tm3+-doped NaGd(WO4)2, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd–Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the 3H4 level was determined to be approximately 65% for this material. The emission cross-section of the 3F4→3H6 IR transition at about 1.8 μm was estimated by the reciprocity method.