Unveiling Mechanism of Temperature‐Dependent Self‐Trapped Exciton Emission in 1D Hybrid Organic–Inorganic Tin Halide for Advanced Thermography

Abstract

Abstract Lead‐free hybrid metal halide phosphors/crystals showing self‐trapped exciton (STE) emission have been recently explored for thermography due to the strong temperature dependence of their photoluminescence (PL) lifetime ( τ ). However, realizing high‐spatial‐resolution thermography using polycrystalline powders or crystals presents a challenge. Moreover, the underlying mechanism of temperature‐dependent STE remains elusive. Herein, a homogeneous 1D ODASn 2 I 6 (ODA, 1,8‐octanediamine) nm‐scale thin film exhibiting efficient STE emission is investigated. The PL decay shows a strong temperature dependence from 275 K ( τ ≈ 1.31 µs) to 350 K (τ ≈ 0.65 µs) yielding a thermal sensitivity of 0.014 K −1 . By employing temperature‐dependent transient absorption spectroscopy, detailed information is obtained about the relaxation processes prior to the STE formation. Simultaneous analyses of steady‐state and time‐resolved spectroscopies lead to a self‐consistent model where the thermally activated phonon‐assisted nonradiative pathway explains the temperature dependence of the PL lifetime via a conical intersection between the ground state and STE potential energy surfaces. Finally, a discernible 50 ns variation in PL lifetimes across different heated regimes over a distance of 1.15 mm is successfully demonstrated with fluorescence lifetime imaging microscopy, underscoring the substantial potential of ODASn 2 I 6 thin film for high‐spatial‐resolution thermography.