Anomalous Antithermal Quenching and Enhanced Thermal Sensitivity in Fractal‐Structured Cs₂NaHoBr₆ Perovskite

Abstract Lead‐free double perovskite (LDP) compounds have emerged as star materials in luminescent materials due to their unique optical properties. Unfortunately, addressing thermal quenching at elevated temperatures and enhancing temperature sensitivity remain substantial challenges. This study presents a Cs 2 NaHoBr 6 LDP, synthesized via an innovative solvent evaporation method. The novel Cs 2 NaHoBr 6 compound exhibits superior dual‐mode feature, showing intense narrow‐band red and near‐infrared emission under 460 or 980 nm excitation. Notably, within the temperature range of 303–583 K, the fluorescence intensity displays an anomalous antithermal quenching behavior, with emissions at 583 K being ≈40 times stronger than that at room temperature. Through in situ solution crystallization, fractal‐structured Cs 2 NaHoBr 6 is successfully prepared, which exhibits thermally enhanced fluorescence intensity. The relative sensitivity of the ordered fractal Cs 2 NaHoBr 6 increased from 0.68% K −1 to 2.60% K −1 compared to the disordered powder, indicating a significant enhancement in temperature sensing capability. The findings offer novel insights into the crystallization behavior and sensing performance optimization of perovskite materials and provide valuable guidance for the development of high‐performance optical temperature sensors.