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

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 W⁴⁺-activated Cs₂ZrCl₆, 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 Cs₂ZrCl₆: W⁴⁺, Ce⁴⁺ 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 W⁴⁺ ion is responsible for excellent thermal stability. Density functional theory calculations confirm that weak transient lattice distortion of isolated [WCl₆]^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.