Effects of Cu²+ doping and pressure on the exchange-mediated exciton dynamics in one-dimensional N(CH₃)₄MnCl₃

Abstract

This work investigates the Mn²+ electronic structure and exciton dynamics in one-dimensional (1D) N(CH₃)₄MnCl³ (TMMC) through time-resolved excitation/emission spectroscopy and absorption measurements in the 0–10 GPa pressure range for different Cu²+ doping concentrations. The local and crystal structures have been analyzed by Raman spectroscopy and x-ray absorption measurements at the Mn K edge showing that the 1D chain structure is maintained in the whole explored pressure range. We show that both the first Mn²+ absorption band, ⁴T₁(G), and its associated emission band experience very large pressure redshifts, which are associated with the crystal anisotropy providing large axial ligand fields at the Mn²+ site that increase with pressure. The red emission at 633 nm shows a large pressure variation of 22 nm/GPa (50 meV/GPa) making TMMC a suitable probe for using as a photoluminescence (PL) pressure gauge in the low-pressure regime. The energy-transfer exciton dynamics and trapping at non-PL centers have been explained through changes of the intrachain Mn-Mn exchange interaction and Cu²+-trap concentration carried out by applying pressure and doping, respectively. The model demonstrates that an increase of exchange interaction favors both the pumping capability and energy transfer yielding exciton migration. Under these conditions, we show that pressure enhances the PL efficiency of TMMC provided that the Cu²+ concentration responsible for the PL quenching is below 0.001 mol %. However, between 0.001% and 0.1%, the PL intensity reduces with pressure, and above 0.1%, the PL is practically quenched even at ambient conditions.