Temperature-independent emission in a [(CH₃)₃NPh]₂MnBr₄ single crystal analogous to thermally activated delayed fluorescence

We demonstrate a novel defect-mediated, thermally-activated emission mechanism in [(CH₃)₃NPh]₂MnBr₄ single crystals, driven by the coexistence of temperature-sensitive shallow traps and temperature-independent deep traps introduced by Br vacancies. Through comprehensive temperature-dependent photoluminescence (PL) and time-resolved PL measurements, combined with first-principles calculations, we reveal that the material exhibits exceptional thermal stability, retaining 67 % of its relative PL quantum yield at room temperature and achieving an absolute quantum yield of ∼38.9 % under optimal excitation conditions. The dual-component PL decay dynamics consist of a fast decay (∼hundreds of ps) governed by shallow traps and a long decay (∼350 μs) dominated by deep traps, creating an energy cascade that efficiently promotes radiative recombination while minimizing non-radiative losses. Our findings provide critical insights into defect-mediated, thermally-sensitive delayed emission mechanisms and establish [(CH₃)₃NPh]₂MnBr₄ as a lead-free, thermally stable material with high efficiency, making it an excellent candidate for next-generation optoelectronic applications, including solid-state lighting and temperature-sensitive devices.