Unveiling\nthe Antithermal Quenching Behavior in 0D\nInorganic Metal Halide Cs<sub>2</sub>InCl<sub>5</sub>(H<sub>2</sub>O) Mediated by Upconversion Emission

Inorganic metal halides (IMHs) often suffer from severe\nfluorescence\nthermal quenching, limiting their application at elevated temperatures.\nTherefore, the exploration of IMHs exhibiting antithermal quenching\n(ATQ) behavior is of great importance. In this study, we developed\na green synthetic route using a solvent evaporation method to successfully\nsynthesize the 0D IMHs Cs<sub>2</sub>InCl<sub>5</sub>(H<sub>2</sub>O). By precise control over the doping ratios of Sb<sup>3+</sup>,\nYb<sup>3+</sup>, and Er<sup>3+</sup>, unique dual-mode emission properties\nare obtained. As the temperature increases, the compound exhibited\ndownconversion and upconversion luminescence, with relative sensitivity <i>S</i><sub>R</sub>-max values of 7.11% K<sup>–1</sup> and\n1.21% K<sup>–1</sup>, respectively. Particularly anomalous\nis the compound’s manifestation of an unconventional ATQ behavior\nduring the upconversion process. <i>In situ</i> structural\nanalysis confirmed that under high-temperature conditions, the 0D\nCs<sub>2</sub>InCl<sub>5</sub>(H<sub>2</sub>O) metal halide undergoes\nstructural evolution, transitioning through a Cs<sub>3</sub>In<sub>2</sub>Cl<sub>9</sub> phase, which is responsible for the ATQ. This\nstudy provides experimental evidence for the abnormal ATQ of 0D metal\nhalides, offering new inspiration for the multifunctionalization of\n0D metal halides in high-temperature temperature sensing and dual-mode\nluminescence.