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Title: Tunable Broadband Emission via Self-Trapped Excitons and Mn2+ Energy Transfer in a 0D Hybrid Manganese Bromide

Authors: P. Peksa*, M. Ptak, M. Dyksik, A. Surrente, M. Baranowski, D. Drozdowski, A. Gągor, J. Osmólska, A. Kuc, A. Pikul, D. Szewczyk, P. Płochocka, A. Sieradzki*

Journal: Small

DOI: 10.1002/smll.202504786   

In this article, structural, phonon, optical, magnetic, and dielectric properties of novel hybrid organic-inorganic crystal of a zero-dimensional bromomethyltrimethylammonium manganese bromide, TMBM₂MnBr₄, are studied as an efficient green phosphor. This material undergoes two structural order-disorder phase transitions responsible for a step-like dielectric behavior and an additional one at 40 K associated with the final ordering or freezing of the cation dynamics. The detailed optical and theoretical studies demonstrated that the observed emission is governed by the interplay between exciton dynamics and cation ordering and includes not only Mn²⁺ d-d transitions but also the self-trapped exciton formation. The competition between self-trapped exciton and energy transfer to Mn²⁺ centers enables tunable emission, while variations in Mn─Br bond lengths across crystallographically distinct tetrahedra modulate crystal field strength and emission energy. The emission properties in external magnetic fields up to 65 T are also discussed. These results into structure-property relationships in low-dimensional manganese halides offer promising ways to design efficient, tunable luminescent materials.

Highlights:

• The 0D TMBM₂MnBr₄ crystal exhibits efficient broad green luminescence.
• The mechanism of STE emission is discussed.
• • The mechanisms of structural phase transitions are explained.