Structure and Property Evolution of Mechanochemical Synthesized Pyrrolidine Incorporated Manganese Bromide Powders

Due to the effects of electron correlation and spin-spin coupling, pure transition metal compounds rarely produce luminescence and ferromagnetism. In this work, the Pb-free perovskite materials, C8H20N2MnBr4 and C4H10NMnBr3 with high luminescence yield were obtained via a simple mechanochemical processing. For C8H20N2MnBr4 powders, MnBr42- coordination with two pyrrolidine molecules to form an independent mononuclear structure in crystal, with paramagnetic property and a strong emission band at 520 nm due to the lowest d-d crystal field radiation transition for individual Mn(II) ion. In C4H10NMnBr3 powders, MnX64- octahedron, coordinated with a much less amount of pyrrolidine molecules than that in C8H20N2MnBr4, form edge-share linear chains of Mn-ion octahedra with much smaller Mn-Mn distance, which produce emission band at 628 nm due to the ferromagnetic coupling Mn pair or cluster. Influenced by the local crystal structure modification by incorporated pyrrolidine molecules, the microcrystals in these two powders exhibit different phase transition temperatures and varied lifetimes in their photoluminescence besides their emission colors. By controlling the processing time of mechanochemical reaction and pyrrolidine amount, the pyrrolidine insertion into the lattice of this transition metal halide can be adjusted to be completely realized, which provides a very simple way to change the ligand from halide ion to organic molecule, which regulates the Mn-Mn distance in lattice, modifying the electronic correlation and spin coupling, thereby obtaining new manganese perovskite compounds with both strong luminescence and clear ferromagnetic properties.