Radiative lifetime and dynamics of trions in few-layered ReS2

Few-layered ReS2 with anisotropic electrical and optical properties has attracted much attention in the research field of two-dimensional (2D) materials. Recently, a stable charged exciton (trion) composed of bound states of two electrons and a hole with large binding energy has been experimentally observed in a few-layered ReS2. However, the dynamics of stable trions remain unclear. We studied the excited-state dynamics, including the radiative lifetime of the negative trion in three layer (3L)-ReS2 via temperature-dependent photoluminescence spectroscopy and phenomenological rate-equation analysis. The derived radiative lifetime of the trion increases linearly with increasing temperature, reaching a few nanoseconds at a high temperature of 150 K; this observation implies that the experimentally observed negative trion in 3L-ReS2 lies in the optically allowed state. Our results provide significant insights into the physics of excitonic states in 2D materials.