Effect of A-Cation Radius on the Structure, Luminescence, and Temperature Sensing of Double Perovskites A2MgWO6 Doped with Dy3+ (A = Ca, Sr, Ba)

Herein, we report a case of A2MgWO6 (A = Ca, Sr, Ba) doped with 2%Dy3+, 2%Li+, in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O2––W6+), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca2+ and Sr2+ ions for larger ions (Ba2+) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy3+, 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 4F9/2 → 6H13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy3+. Moreover, the thermal sensing properties of 2%Dy3+-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.