Regulating Exciton De‐Trapping of Te ⁴⁺ ‐Doped Zero‐Dimensional Scandium‐Halide Perovskite for Fluorescence Thermometry with Record High Time‐Resolved Thermal Sensitivity

Abstract Fluorescence thermometry has been propelled to the forefront of scientific attention due to its high spatial resolution and remote non‐invasive detection. However, recent generations of thermometers still suffer from limited thermal sensitivity ( S _r ) below 10% change per Kelvin. Herein, this work presents an ideal temperature‐responsive fluorescence material through Te ⁴⁺ ‐doped 0D Cs ₂ ScCl ₅ ·H ₂ O, in which isolated polyhedrons endow highly localized electronic structures, and the strong electron–phonon coupling facilitates the formation of self‐trapped excitons (STEs). With rising temperature, the dramatic asymmetric expansion of the soft lattice induces increased defects, strong exciton–phonon coupling, and low thermal activation energy, which evokes a rapid de‐trapping process of STEs, enabling several orders of magnitude changes in the fluorescence lifetime over a narrow temperature range. After regulating the de‐trapping process with different Te ⁴⁺ doping, a record‐high S _r (27.36% K ⁻¹ ) of fluorescence lifetime‐based detection is achieved at 325 K. The robust stability against multiple heating/cooling cycles and long‐term measurements enables a low temperature uncertainty of 0.067 K. Further, the developed thermometers are demonstrated for the remote local monitoring of operating temperature on internal electronic components. It is believed that this work constitutes a solid step towards building the next generation of ultrasensitive thermometers based on low‐dimensional metal halides.