Pressure effects on the crystal field and luminescence Stokes shift of Mn2+ (Td) in [(CH3)4N]2MnX4 (X: Cl, Br) by time-resolved spectroscopy

This work investigates the Mn2+ electronic structure and photoluminescence (PL) in [(CH3)4N]2MnCl4 and [(CH3)4N]2MnBr4 and their variation with pressure by time-resolved excitation and emission spectra in the 0–10 GPa range. We show that both the crystal-field excitation and corresponding PL bands experience large-pressure redshifts (about 5 nm/GPa), which are associated with the high crystal compressibility and the interaction between organic/inorganic ([CH3]4N−/MnX) tetrahedra. The energy variation as a function of pressure is explained in terms of the isolated Td MnX in the respective crystals through crystal-field models. One salient feature is the reduction of the PL Stokes shift with pressure in both crystals as−1.0 and−1.7 nm/GPa for chloride and bromide, respectively.