Erbium-Induced Boost in Self-Trapped Exciton Emission of Double Perovskites for Highly Sensitive Multimodal and Multiplexed Optical Thermography

Self-trapped excitons (STEs) of lead-free perovskites have aroused tremendous interest in remote optical thermometry due to strong exciton–phonon coupling and large Stokes shifts. Herein, a bright multimodal and multiplexed optical thermometer is constructed with high sensitivity ( S r ) and self-calibrating ability based on Cs 2 NaInCl 6 :Er 3+ double perovskite, allowing for fast and simplified reading via mobile devices. Intriguingly, Er 3+ doping not only shows the characteristic green emissions but also introduces nanoelectronic domains through a new localized valance band maximum and breaks the symmetry of In 3+ site, which facilitates the generation of more STEs. The temperature-sensitive blue emission of STEs and temperature-insensitive green emission of Er 3+ endow multimodal optical thermometry including time-resolved and ratiometric readout schemes with a maximum S r of 3.8% K −1 , where an upconversion primary thermometry serves as a reference to calibrate other modes. Meanwhile, the designed thermometers show robust photostability, repeatability, and structural stability for long-time working and storage. In addition, the remarkable thermochromic phenomenon from blue to green enables a quick color-multiplexed thermography on a smartphone, which is utilized to capture real-time 2D thermal imaging of microelectronic devices. This work demonstrates the great potential of lead-free double perovskite for low-cost and portable optical thermometry.