Unveiling the Antithermal Quenching Behavior in 0D Inorganic Metal Halide Cs₂InCl₅(H₂O) Mediated by Upconversion Emission

Inorganic metal halides (IMHs) often suffer from severe fluorescence thermal quenching, limiting their application at elevated temperatures. Therefore, the exploration of IMHs exhibiting antithermal quenching (ATQ) behavior is of great importance. In this study, we developed a green synthetic route using a solvent evaporation method to successfully synthesize the 0D IMHs Cs₂InCl₅(H₂O). By precise control over the doping ratios of Sb³⁺, Yb³⁺, and Er³⁺, unique dual-mode emission properties are obtained. As the temperature increases, the compound exhibited downconversion and upconversion luminescence, with relative sensitivity <i>S</i>_R-max values of 7.11% K^-1 and 1.21% K^-1, respectively. Particularly anomalous is the compound's manifestation of an unconventional ATQ behavior during the upconversion process. <i>In situ</i> structural analysis confirmed that under high-temperature conditions, the 0D Cs₂InCl₅(H₂O) metal halide undergoes structural evolution, transitioning through a Cs₃In₂Cl₉ phase, which is responsible for the ATQ. This study provides experimental evidence for the abnormal ATQ of 0D metal halides, offering new inspiration for the multifunctionalization of 0D metal halides in high-temperature temperature sensing and dual-mode luminescence.