Reconstructive Phase Transition Enabled Second Harmonic Generation and Switchable Photoluminescence of a Hybrid Metal Halide for Temperature Sensing and Anticounterfeiting

Organic-inorganic hybrid metal halides (OIHMHs) provide a highly tunable platform for engineering optical properties thanks to their rich structural diversity and chemical versatility. Herein, we report a zero-dimensional Mn-based OIHMH that undergoes a thermally driven reconstructive phase transition via the breaking of coordination bonds between the organic cations and the metal center. This transition not only activates second harmonic generation (SHG) in the high-temperature phase but also induces a pronounced blue shift in photoluminescence from approximately 630 to 550 nm and a great reduction of lifetime from 5.23 to 2.22 ms. The resulting remarkable photoluminescence tunability is further demonstrated in applications such as temperature sensing and anticounterfeiting. This study offers a compelling example of an OIHMH whose SHG and photoluminescence properties can be significantly modulated via a reconstructive phase transition, providing valuable insights for the design of stimuli-responsive materials for next-generation sensing and smart devices.