Publication date: 22nd July 2026
Organic–inorganic hybrid manganese halides are promising lead-free luminescent materials for optoelectronic applications because of their high photoluminescence quantum yields, structural versatility, and thermal stability. In low-dimensional manganese halides, such as TMA₂MnBr₄, local structural distortions and molecular dynamics can give rise to multiple emissive channels and temperature-dependent switching between emissive states. However, how thermally driven structural transitions affect excitation-dependent photoluminescence remains poorly understood.
Here, we show that TMA₂MnBr₄ exhibits two emissive channels, including a low-energy channel that emerges at low temperature. The two emissions appear to arise from related excited states and may represent competing relaxation pathways. Temperature-dependent photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy identified the characteristic green Mn²⁺ emission centred at 520 nm and an additional low-energy (LE) band at 590–620 nm that appeared only in the low-temperature phase below 20 K, which evolves with the excitation wavelength. To investigate the origin of this dual emission, we measured PL spectra under 422 nm excitation as a function of temperature and analysed the integrated intensity of each band. The low-energy emission underwent thermal quenching with an activation energy of approximately 4 meV. At 5 K, the two bands showed anticorrelated changes in intensity, suggesting competing radiative pathways and possible energy transfer between the associated excited states. This behaviour is consistent with a self-trapped-exciton-like state stabilised by the rigid low-temperature lattice.
This work highlights the role of low-temperature ordering in the emergence of additional emissive states in low-dimensional Mn²⁺-based materials and may help guide the design of next-generation lead-free optoelectronic materials.
This work was supported by the National Science Centre, Poland grants SONATA 19 no. 2023/51/D/ST5/02836 and OPUS 21 no. 2021/41/B/ST5/01684
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