Tunable Broadband Emission via Self‐Trapped Excitons and Mn ²⁺ Energy Transfer in a 0D Hybrid Manganese Bromide

Abstract A novel 0D organic–inorganic hybrid manganese bromide, (TMBM) ₂ MnBr ₄ , based on bromomethyltrimethylammonium (TMBM) cations and isolated [MnBr ₄ ] ² ⁻ tetrahedra, is synthesized and structurally characterized. The material undergoes two temperature‐induced phase transitions and exhibits intense broadband green photoluminescence at low temperatures. Detailed structural, spectroscopic, and thermodynamic analyses reveal that the emission behavior is governed by the interplay between exciton dynamics and cation ordering. The competition between self‐trapped exciton (STE) formation and energy transfer to Mn ² ⁺ centers enables tunable emission, while variations in Mn─Br bond lengths across crystallographically distinct tetrahedra modulate crystal field strength and emission energy. These insights into structure–property relationships in low‐dimensional manganese halides offer promising avenues for the design of efficient, tunable luminescent materials and multifunctional magneto‐optical devices.