Nonlinear photoluminescence in atomically thin layeredWSe2arising from diffusion-assisted exciton-exciton annihilation

We studied multiexciton dynamics in monolayer ${\mathrm{WSe}}_{2}$ using nonlinear photoluminescence (PL) spectroscopy and Monte Carlo simulations. We observed strong nonlinear saturation behavior of exciton PL with increasing excitation power density and long-distance exciton diffusion, reaching several micrometers. We demonstrated that the diffusion-assisted exciton-exciton annihilation (EEA) model accounts for the observed nonlinear PL behavior. The long-distance exciton diffusion and subsequent efficient EEA process determined the unusual multiexciton dynamics in atomically thin layered transition metal dichalcogenides.