Magnetic-excitation-assisted photoluminescence from self-trapped exciton states in MnO

摘要

We examined the photoluminescence (PL) in single-crystal MnO(111) and observed a new strong emission band with a high-energy-side edge of 1.905 eV below 20 K. The emission bands with high-energy-side edges of 1.875 eV and 1.815 eV were also observed between 20 K and 30 K, and above 40 K, respectively. The temperature dependence of the intensity of each PL band showed step-like decreases at different critical temperatures, which suggests that the emission spectrum consist of contributions from three independent excited states. The fine structures of emission sidebands in the PL spectrum were interpreted in terms of phonons and magnons coupled with three types of self-trapped exciton (STE) states. Based on the Stokes shifts observed in our experiments and the thermal activation energies estimated from the temperature dependence of the PL intensity, we propose a configuration coordinate diagram for STE states and explain the mechanism of radiative and nonradiative relaxations in the magnetic-excitation-assisted PL process from the three types of STE states.