Broad-Temperature Optical Thermometry via Dual Sensitivity of Self-Trapped Excitons Lifetime and Higher-Order Phonon Anharmonicity in Lead-Free Perovskites

Broad-temperature optical thermometry necessitates materials with exceptional sensitivity and stability across varied thermal conditions, presenting challenges for conventional systems. Here, we report a lead-free, vacancy-ordered perovskite Cs2TeCl6, that achieves precise temperature sensing through a novel combination of self-trapped excitons (STEs) photoluminescence (PL) lifetime modulation and unprecedented fifth-order phonon anharmonicity. The STEs PL lifetime demonstrates a highly temperature-sensitive response from 200 to 300 K, ideal for low-to-intermediate thermal sensing. In contrast, the Eg phonon mode undergoes significant linewidth broadening due to five-phonon scattering processes, with a distinct nonlinear temperature dependence up to 500 K. This fifth-order anharmonic effect enhances Raman-based temperature sensitivity, yielding a specific sensitivity (Sr) of 0.577% K−1 at 330 K and remaining above 0.5% K−1 at elevated temperatures. This study presents the first evidence of fifth-order anharmonic effects enhancing Raman-based temperature sensitivity, establishing Cs2TeCl6 as a versatile candidate for broad-temperature optical thermometry and opening new avenues for precise non-contact temperature sensing in advanced technological applications.