A highly sensitive ratiometric optical thermometer based on a Sr₂MgWO₆ double perovskite doped with Dy³⁺ exploiting thermally coupled and uncoupled levels

The increasing demand for highly sensitive optical thermometers operating within a wide temperature range necessitates the development of new phosphors. In this work, the potential temperature sensing performance of a novel yellow-emitting phosphor, Sr₂MgWO₆ double perovskite, doped with varying concentrations of Dy³⁺ was investigated for the first time. Increasing the concentration of Dy³⁺ from 0% to 7% shifted the color of luminescence from blue to yellowish-orange within the CIE1931 color space. The energy transfer efficiency from (WO₆)^6- to Dy³⁺ also increased significantly to 98.4%. Moreover, the sample doped with 3% Dy³⁺ showed the highest emission intensity, with a concentration beyond this threshold inducing concentration quenching. This phenomenon was primarily governed by dipole-dipole interactions. The highest quantum yield was found to be 30.7% for the sample doped with 3% Dy³⁺. Upon 266 nm wavelength excitation, the temperature sensing ability of the samples doped with 3%, 5%, and 7% Dy³⁺ was examined based on the fluorescence intensity ratio between the thermally coupled and uncoupled levels. It showed that the relative thermal sensitivity of <i>S</i>_r can be tuned by changing the Dy³⁺ concentration. <i>S</i>_r-max = 3.24% K^-1 was obtained for the sample doped with 3% Dy³⁺ at 193 K within the 80-273 K operating range for thermally uncoupled levels. For thermally coupled levels, the <i>S</i>_r-max value reached 1.35% K^-1 at 333 K for the sample doped with 7% Dy³⁺ in the range of 293-593 K. These results demonstrate the enormous potential of the studied materials for thermal sensing applications.