A comparison of spectroscopic properties of Dy³⁺-doped tetragonal tungsten bronze MTa₂O₆ (M = Sr, Ba, Pb) phosphors based on Judd–Ofelt parameters

TTB (tetragonal tungsten bronze) crystal structures exhibit very interesting physical properties as well as the superiority of having different cationic sites and allowing doping. In the study, the spectroscopic results of TTB-MTa₂O₆:Dy³⁺ (M = Sr, Ba, Pb) phosphors are presented using Judd–Ofelt (JO) intensity parameters. The PL and RL spectra of the phosphors exhibited the characteristic emissions of Dy in the visible and infrared regions. The PL excitation spectra were used to determine JO parameters (Ω₂, Ω₄, Ω₆). The decreasing trend of Ω₂ parameter and PL asymmetry is SrTa₂O₆:Dy³⁺ > PbTa₂O₆:Dy³⁺ > BaTa₂O₆:Dy³⁺, which shows low electronegativity and shifting to the long wavelength of BaTa₂O₆:Dy³⁺ supports the low value of the Ω₂ parameter and covalence. The PL decay profiles of all the phosphors are double exponential and the fast decreasing of PL decay components of SrTa₂O₆:Dy³⁺ is compatible with the concentration quenching after 5 mol%. The decreasing trend of the observed lifetime is in order BaTa₂O₆:Dy³⁺  > PbTa₂O₆:Dy³⁺  > SrTa₂O₆:Dy³⁺, which can be attributed to the defect centers depending on the increase of the covalency.