Defect-Mediated Exciton Localization and Relaxation in Monolayer MoS₂

Defects in chemical vapor deposition (CVD)-grown monolayer MoS₂ are unavoidable and provide a powerful approach to creating single-photon emitters and quantum information systems through localizing excitons. However, insight into the A^- trion and B/C exciton localization in monolayer MoS₂ remains elusive. Here, we investigate defect-mediated A^- trion and B/C exciton localization and relaxation in CVD-grown monolayer MoS₂ samples via transient absorption spectroscopy. The localization rate of A^- trions is five times faster than B excitons, which is attributed to the distinctions in the Bohr radius, diffusion rate, and multiphonon emission. Furthermore, we obtain unambiguous experimental evidence for the direct excitation of localized C excitons. Varying gap energy at the band-nesting region revealed by first-principles calculations explains the anomalous dependence of localized C exciton energy on delay time. We also find that the rapid dissociation of localized C excitons features a short characteristic time of ∼0.14 ps, while the measured relaxation time is much longer. Our results provide a comprehensive picture of the defect-mediated excitonic relaxation and localization dynamics in monolayer MoS₂.