The development of a dual-mode optical temperature sensor based on fluorescence intensity ratio and lifetime

The utilization of optical parameters is crucial for achieving accurate temperature detection, which in turn facilitates the development of new phosphors used for non-contact optical thermometers. In this study, a series of phosphors of KSrGdTeO6 (KSGT) co-doping Mn4+ and Sm3+ luminescent centers, were synthesized through high temperature solid-state reactions. Notably, the temperature-dependent emission spectra and attenuation curves of KSGT:Mn4+/Sm3+ were measured across a wide temperature range of 298–573 K. In the absence of energy transfer between Mn4+ and Sm3+, Mn4+ and Sm3+ activators can emit their characterized emissions by 405 nm excitation. With increasing temperature, the fluorescence intensity of Mn4+ ions decreases at a faster rate compared to that of Sm3+ ions as the temperature increases. Consequently, by utilizing the fluorescence intensity ratio (FIR) between the two activators Mn4+ and Sm3+, the optimal temperature sensing relative sensitivity (Sr) and absolute sensitivities of (Sa) of KSGT:Mn4+/Sm3+ were found to be 2.591 % K−1 at 298 K and 0.0246 K−1 at 573 K. Moreover, the luminescent lifetime of Mn4+ emission decreases rapidly with increasing temperature, which makes it also possible to be a lifetime-based thermometry with Sa and Sa of 2.3233 %K−1 at 448 K and 0.1444 K−1 at 398 K. The dual-mode sensing properties of KSGT:Mn4+/Sm3+ make it a highly sensitive temperature thermometer, which provides design ideas for future researchers in this field.