Dual‐Mode Optical Thermometers Based on the Thermal‐Stable Perovskite Nanocrystals Embedded in Robust Metal Halide Salts

Photothermal sensing is crucial for the creation of smart integrated devices. All‐inorganic metal halide perovskites with the formula CsPbX 3 (X═Cl, Br, I) have excellent photo‐physical performance, offering exciting opportunities for flexible electronics. Hence, a supersaturated precipitation strategy is proposed for the preparation of salt‐shelled metal halide solids. The well‐designed CsPbX 3 @MX (M═K, Cs) products exhibit bright narrow visible emissions and favorable thermal stability up to 195 °C. Co‐doping with Ni 2+ and Mn 2+ ions, the CsPbCl 3 @KCl products have realized dual‐mode thermometry. Utilizing the blue emission from the CsPbCl 3 host and the red emission from the Mn 2+ ion, a fluorescence intensity ratio technique is obtained to monitor the temperature of good stability and repeatability. Based on the regular fluorescence decay of Mn 2+ ions with rising temperature, the lifetime of Mn 2+ ions can also be used for temperature sensing. It is believed that such stable metal halides with dual‐mode thermometry will provide a new sight for optical thermometers and, more importantly, will unleash the possibility of a broad variety of applications in lightweight and integrated functional devices.