Effect of temperature on host emission and ratiometric thermometry in Dy(III) doped tungstate double perovskite

Abstract

Non-contact ratiometric thermometers owing to thermally coupled energy levels (TCLs) are in high demand due to higher precision and temperature sensitivity. Here, Dy³⁺ activated Mg₃WO₆ down-converting phosphors were investigated for temperature sensing within 303–498 K. Dy³⁺ concentration was varied from 0.5 to 2.5 mol%, and all the phosphors were synthesized via the solid-state reaction at 1200 °C. When excited at 278 nm, the phosphors exhibited tungstate host emission at 473 nm along with Dy³⁺ emissions at 490 nm (⁴F_9/2-⁶H_15/2) and 575 nm (⁴F_9/2-⁶H_13/2), wherein host emission dominated the emission spectrum. The phosphors examined for luminescence decay displayed a reduction in decay lifetime with increasing Dy³⁺ concentration. The temperature-dependent photoluminescence (TDPL) spectra obtained within 303–498 K showed steady decrease in PL intensity of host emission and ⁴F_9/2-⁶H_15/2 (490 nm) emission due to thermal quenching. In contrast, the PL intensity of ⁴F_9/2-⁶H_13/2 (575 nm) transition initially increased before eventually decreasing. This behavior is collectively attributed to the energy transfer efficiency from host emission to activator (Dy³⁺) at higher temperatures and the thermal quenching effect on ⁴F_9/2-⁶H_13/2 Dy³⁺ transition. Utilizing fluorescence intensity ratio (FIR) of TCLs (here 490 nm and 575 nm), the thermometry features were examined and discussed. The highest relative sensitivity is obtained to be 1.91 %K⁻¹ at 303 K, whereas the absolute sensitivity was calculated to be 2.07 %K⁻¹ at 473 K, indicating the suitability of the phosphor in temperature sensing within 303–498 K. Moreover, experiments on the repeatability of FIR confirm the reliability of the studied optical thermometer.