Photoexcited d ‐electron dynamics in transition metal oxide MnO studied by optical pump‐THz probe measurements

Optical pump-THz probe (OPTP) measurements allow us to investigate the dynamic response of photoconductivity in materials by observing the transient change of THz transmittance after optical excitation. In this study, the THz response of d -electrons in various photoexcited states in MnO was investigated by pump-energy-tunable OPTP measurements to elucidate the photoexcited d -electron dynamics in a transition metal oxide. At room temperature, photoexcited d -electrons induced by a d -d transition to the lowest excited d -state showed the longest relaxation time. The relaxation time decreased drastically below the antiferromagnetic transition temperature of 120 K. This decrease was accompanied by the emergence of magnetic-excitation-assisted photoluminescence from a self-trapped exciton (STE) state. This suggests that photoexcited d -electrons relax to the STE state below the transition temperature. These findings shed new light on the photoexcited d -electron dynamics, contrasting with the behavior of photoexcited carriers generated in the upper excited d -states that have been shown in a previous study to relax into trap states through carrier scattering. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)