Controlling Quasiparticle Population Dynamics in WS ₂ Monolayer Using Optical Pumping

ABSTRACT Controlling the quasiparticle population density in 2D materials is crucial for designing next‐generation devices. In this study, we explore how optical pumping effectively controls the population and dynamics of quasiparticles (excitons, trions, and biexcitons) in exfoliated and CVD‐grown WS 2 monolayers at room temperature. Photoluminescence analysis reveals that the emission profile primarily consists of excitons and trions in the low‐pump power regime. The densities of the unbound electrons follow the law of mass action, and the trion population increases with increasing pump power. Furthermore, the excitation‐energy‐dependent conversion efficiency is systematically investigated and found to be consistent with pump energy. In the high‐power regime, photoluminescence spectra reveal the formation of biexcitons and defect states, as confirmed by Raman measurements. Additionally, lifetime measurements are performed to assess variations in the radiative and non‐radiative contributions by varying the pump power, which are correlated with steady‐state measurements. Spectral diffusion and bleaching experiments reveal a higher purity of the exfoliated monolayer compared to the CVD‐grown samples. These findings are crucial for designing high‐performing 2D material‐based devices.