Two organic ligands for tuning the luminescence of Mn-based metal halides

Organic-inorganic metal halides (OIMHs) have garnered significant attention due to their rich optical properties and potential applications in light-emitting diodes, display devices, solar cells, and photodetectors. In this work, isopropyltriphenylphosphonium bromide and 1-methyl-1-propylpiperidinium bromide were employed as organic ligands and introduced into the [MnBr 4 ] 2- tetrahedral structure, synthesizing two manganese-based organic-inorganic metal halide single crystals: (C 21 H 22 P) 2 MnBr 4 and (C 9 H 20 N) 2 MnBr 4 , via the anti-solvent vapor diffusion method. Their nearest-neighbor Mn 2+ distances are 11.23 Å and 9.69 Å, which effectively modulates electron-phonon coupling and magnetic interactions, giving distinct green emissions centered at 509 nm and 534 nm under 284 nm and 362 nm excitation, with high photoluminescence quantum yields (93% and 86%) and long luminescence lifetimes (295 μs and 390 μs), respectively. The emission of (C 21 H 22 P) 2 MnBr 4 is dominated by self-trapped excitons (STEs) assisted by magnetic polaron effects, while (C 9 H 20 N) 2 MnBr 4 exhibits pure Mn 2+ d–d transition emission. Furthermore, based on the (C 21 H 22 P) 2 MnBr 4 single crystal, the corresponding amorphous material was prepared via a melting–rapid solidification method, which exhibits an emission peak redshift at 10 nm and a photoluminescence quantum yield of 50%. Through temperature-dependent photoluminescence spectroscopy and X-ray diffraction spectroscopy, the optical and structural properties of the three OIMH materials at low temperatures were systematically characterized, revealing the regulatory effects of magnetic polaron effect and different organic ligand confinement effects on the Mn luminescence, as well as the varied lattice symmetry tuning role of the same organic ligand order on the luminescence behavior.