Vibronically Coupled and Thermally Tunable Broadband NIR Optical Response in 0D W ⁴⁺ ‐Activated Cs ₂ ZrCl ₆ Perovskite for Multifunctional NIR Spectroscopy Applications

Abstract Low‐dimensional halide perovskites are highly susceptible to thermal quenching (TQ) due to strong soft lattice nature. Currently, examples of thermally enhanced NIR luminescence in low‐dimensional materials are very scarce to the knowledge. Herein, the active role of vibronic coupling is manifested through thermal tunability of broadband NIR emission in 0D W ⁴⁺ ‐activated Cs ₂ ZrCl ₆ , leading to anti‐TQ behavior ranging from 80 to 613 K. Interestingly, the internal quantum efficiency is dramatically boosted from 55.9% to 92.9% in Cs ₂ ZrCl ₆ : W ⁴⁺ , Ce ⁴⁺ while retaining zero‐TQ luminescence between 303 and 423 K. Transient‐state spectroscopy reveal the distribution of thermally released charge carriers among the vibronically coupled d ‐electronic states of W ⁴⁺ ion is responsible for excellent thermal stability. Density functional theory calculations confirm that weak transient lattice distortion of isolated [WCl ₆ ] ^2– octahedra in the excited state can combat TQ enabled by Franck–Condon vibronic coupling. Utilizing this thermal‐tolerant characteristic, both bandwidth‐ and lifetime‐based thermometers have been developed with low temperature uncertainties below 0.12 K. Moreover, NIR spectroscopy‐type sensor is presented for quantitative HF gas detection with concentration‐ and temperature‐dependent high sensing response and low detection limit. These findings may provide a vital insight into vibronic coupling‐assisted heat‐favorable NIR emissions in low‐dimensional materials for versatile applications.