Effect of Sr2+ ions on the structure, up-conversion emission and thermal sensing of Er3+, Yb3+ co-doped double perovskite Ba(2−x)SrxMgWO6 phosphors

Investigating the effect of different phases on the optical performance is crucial for thermal sensing phosphor materials. Ba(2-x)SrxMgWO6:Er3+, Yb3+, K+ double perovskite phosphors were successfully prepared using a high-temperature solid-phase method. The dominant up-conversion luminescent (UCL) mechanism was deduced by analyzing the power-dependence spectra and energy level diagrams. By X-ray diffraction tests and tolerance factor calculations, it was demonstrated that the substitution of Sr2+ ions for Ba2+ ions led to the phase changing from cubic to tetragonal. The phase transition led to a decrease in the crystallographic symmetry of the compounds and changes in the optical thermometric properties. The optical temperature sensing properties were investigated using the fluorescence intensity ratio of thermally coupled energy levels (2H11/2 and 4S3/2 to the ground state energy level 4I15/2) of Er3+ ions in Ba2MgWO6, BaSrMgWO6 and Sr2MgWO6. The maximum absolute sensitivities obtained for Ba2MgWO6, BaSrMgWO6 and Sr2MgWO6 doped with 7% Er3+, 2% Yb3+ and 9% K+ were 6.77 × 10-4 K-1, 10.09 × 10-4 K-1 and 23.4 × 10-4 K-1, respectively. The comparison revealed that the phase transition caused an increase in the luminescence intensity and absolute sensitivity. This provides a useful pathway for modulating the subsequent thermometric performance.