Long-lived photogenerated carriers in MoS₂flakes chemically exfoliated.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS₂ and WS₂ are excellent candidates for next generation energy storage and optoelectronics due to their strong light-matter interaction.

The preparation of monolayer TMDs by mechanical exfoliation is a labour-intensive process and the yield is low. An alternative top-down approach, which may be more suitable for industry, is the liquid phase exfoliation technique (LPE) which can produce an extremely high yield with reasonable quality.

In this study, we investigate LPE MoS₂ samples using time-resolved optical spectroscopy. The transient response of these materials is dictated by the formation and recombination of bound states, e.g. excitons, trions and biexcitons. Using a specially designed pump-probe setup, we measure the lifetime of these photoexcited states from the femtosecond (10^-15 s) to microsecond range (10^-6 s). Pumping at 3.5 eV, we observe spectral features which exhibit dynamics up to ~ 100 ns. Understanding the origin of complex physical processes in this temporal range is crucial for applications which rely on long-lived states.