Customizable Superior Performance via Managing Defect and Self‐Trapped Exciton Interactions in Zinc‐Based Metal Halides for Multifunctional Applications

Self‐trapped exciton (STE) luminescent materials attract considerable research interest in optoelectronic applications. However, their practical implementation is hindered by thermal quenching effects arising from strong electron–phonon interactions. A defect engineering strategy based on high‐temperature reactions is proposed to regulate the thermal response, successfully achieving a performance breakthrough in Rb 3 ZnCl 5 :Sn 2+ phosphors. By suppressing Zn Rb antisite luminescence centers ( λ em = 430 nm) and enhancing thermally activated energy recombination from chlorine vacancy defect levels under Rb‐rich conditions, the STE emission peaked at 610 nm achieves near‐unity internal quantum efficiency (98%) and zero‐thermal‐quenching property from 25 to 175 °C, demonstrating excellent potential for white light‐emitting diode applications. Additionally, by controlling the increase of Zn Rb antisite, the enhanced blue defect emission give the material a dual‐emission characteristic, a visual temperature sensor based on the fluorescence intensity ratio I 430nm / I 610nm is designed, showcasing a blue‐to‐orange color transformation and an ultra‐high maximum sensitivity of 8.64% K −1 within the temperature range of 77 to 302 K. First principles calculations and in situ temporal response curve analysis reveals that these dramatic variations are related to temperature‐induced energy migration process, influenced by STE formation and electron recombination. This research offers new insights for designing high‐performance STE luminescent materials.