Effect of Sr 2+ ions on the structure, up-conversion emission and thermal sensing of Er 3+ , Yb 3+ co-doped double perovskite Ba (2- x ) Sr x MgWO 6 phosphors.

Investigating the effect of different phases on the optical performance is crucial for thermal sensing phosphor materials. Ba (2- x ) Sr x MgWO 6 :Er 3+ , Yb 3+ , 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 Sr 2+ ions for Ba 2+ 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 ( 2 H 11/2 and 4 S 3/2 to the ground state energy level 4 I 15/2 ) of Er 3+ ions in Ba 2 MgWO 6 , BaSrMgWO 6 and Sr 2 MgWO 6 . The maximum absolute sensitivities obtained for Ba 2 MgWO 6 , BaSrMgWO 6 and Sr 2 MgWO 6 doped with 7% Er 3+ , 2% Yb 3+ 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.