Fermi level dependence of ultrafast time-resolved luminescence from single-layer graphene

The photoluminescence (PL) from single-layer graphene has been observed under femtosecond laser pulse excitation. The PL is expected to depend on the Fermi level (E_F). An elucidation of the E_F dependence of PL intensity is important from the viewpoint of future device applications. In this research, we focus on the ultrafast PL from graphene in the near-infrared energy region and clarify the E_F dependence of the PL intensity. To control the E_F of graphene, we used the electrochemical doping technique using an ionic liquid [EMIM][TFSI]. We measured the time-resolved PL using the frequency up-conversion method. The experiments were performed with excitation energy of 1.55 eV and emission energy of 0.9 eV. Here, the E_F of graphene was varied from approximately -0.6 eV to +0.2 eV. We observed a change in the PL intensity with doping level. Based on the results, we discuss the origin of the PL depending on the Fermi level.