Visible TADF and NIR Quenching Emission of Chromium Activated Zirconium‐Halide Perovskite Toward Ultra‐High‐Sensitive Ratiometric Fluorescent Thermometer

Abstract With the development of science and technology, the measurement of temperature is receiving more and more attention. However, ratiometric fluorescent thermometers based on thermally coupled energy levels remain challenging because of their low relative sensitivity ( S r ). In this work, chromium activated zirconium‐halide perovskite Cs 2 ZrCl 6 microcrystals are successfully synthesized via a simple co‐precipitation method at room temperature. Interestingly, the host Cs 2 ZrCl 6 exhibits reverse thermal quenching due to its thermal‐activated delayed fluorescence (TADF) behavior, while the Cr 3+ dopant shows normal thermal quenching. Leveraging the difference in their temperature‐dependent luminescent properties, a ratiometric fluorescent thermometer is ingeniously developed, whose S r reaches a maximum of 4.23% K −1 . Besides, the as‐synthesized thermometer is demonstrated for mobile phone remote temperature measurement. This finding offers a new approach for the design of high‐sensitivity ratiometric fluorescent temperature sensors.