Effect of A-Cation Radius on the Structure, Luminescence, and Temperature Sensing of Double Perovskites A 2 MgWO 6 Doped with Dy 3+ (A = Ca, Sr, Ba).

Herein, we report a case of A 2 MgWO 6 (A = Ca, Sr, Ba) doped with 2%Dy 3+ , 2%Li + , in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O 2- -W 6+ ), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca 2+ and Sr 2+ ions for larger ions (Ba 2+ ) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy 3+ , tuned the color of the emitted light from the whitish to yellowish region, and caused a blue shift of the CTB. Furthermore, a significant decline in the lifetime of the 4 F 9/2 → 6 H 13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy 3+ . Moreover, the thermal sensing properties of 2%Dy 3+ -doped samples were investigated based on the fluorescence intensity ratio technique in the range of 80-325 K. Under 266 nm excitation wavelength, the maximum relative sensitivity of the investigated samples was remarkably enhanced from 2.26%/K, 3.04%/K, to 4.38%/K corresponding to Ba, Ca, and Sr samples, respectively. In addition to providing a comprehensive understanding of the effects of compositional modifications on the optical properties, the results also present a viable pathway to manipulate the temperature sensing performance.