Progressive pressure-induced transformation from isolated MnX4 (Td) to exchange-coupled MnX6 (Oh) systems in A2MnX4 (X:Cl,Br) crystals

This work reports a correlation study between the crystal structure and photoluminescence (PL) in A2MnX4 (A: [CH3]4N; X: Cl, Br) by means of simultaneously optical spectroscopy and x-ray diffraction (XRD) under pressure. These materials are attractive systems for PL studies under pressure since they are very compressible and the interaction between organic/inorganic ((CH3)4N-/MnX42-) tetrahedra strongly affects the PL efficiency, which is fully related to the isolated Td MnX42-. We show that pressure induces strong redshifts of emission peak of MnX42- as well as decomposition processes at higher pressures yielding new aggregated phases of Mn2+ and amorphization which deeply affect Mn2+ PL. The equation of state of each compound is reported from XRD data.