Dynamics of photoexcited carriers in monolayer epitaxial graphene probed by photoluminescence in the near-infrared region

We investigate the dynamics of photoexcited carriers in a single monolayer graphene at room temperature in air by femtosecond time-resolved luminescence measurements. The luminescence kinetics observed in the near-infrared region from 0.7 to 0.9 eV are analyzed based on the two-temperature model describing the cooling of thermalized carriers due to the carrier-optical-phonon coupling. The observed luminescence kinetics are well reproduced by the model, though the calculated electron temperature increases only to ∼420 K at the maximum, which is much lower than the optical phonon energies. This indicates the predominance of optical phonons over acoustic phonons in the carrier-phonon interaction even at a temperature of ∼400 K.