Transition metal dichalcogenides are expected to be used in transparent, flexible, and highly efficient light-emitting devices. Exciton diffusion is a key factor in device applications. In this study, we measured the photoluminescence (PL) decay of excitons in a ${\mathrm{MoS}}_2$ monolayer synthesized by chemical vapor deposition on a sapphire substrate. The PL decay of A and B excitons in the femtosecond regime was observed. The PL decay curves were analyzed based on a model of exciton trapping at the deactivation center via diffusion, and the diffusion time until trapping was obtained. The diffusion coefficient and the corresponding exciton mobility were also determined. This study demonstrates the two-dimensional exciton diffusion in the femtosecond regime in the ${\mathrm{MoS}}_2$ monolayer.

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• 2-dimensional systems
• Dichalcogenides
• Femtosecond laser spectroscopy
• Time-resolved photoluminescence