Long room-temperature valley lifetimes of localized excitons in MoS₂ quantum dots

Transition metal dichalcogenides (TMDs), which exhibit valley polarization characteristics, are very promising materials for the realization of valleytronic devices. To implement practical applications, a long valley lifetime at room temperature is necessary. Here, we demonstrate that diethylenetriamine (DETA)-functionalized MoS 2 quantum dots (QDs) exhibit long valley lifetimes for localized excitons at room temperature. Based on polarization-resolved photoluminescence (PL) dynamics, the degree of circular polarization of defect-bound localized excitons in MoS 2 QDs are found to be between 21% and -22%. The observed room-temperature valley lifetimes for excitons in MoS 2 QDs are more than 58 ns, much larger than those in MoS 2 monolayers (≤ 4 ps). The decay of polarization-resolved PL and the dynamical degree of circular polarization can be modeled by using a rate equation approach. This model is based on intervalley scattering in dark exciton states and relaxation from dark exciton states to localized exciton states. Such a long-lived valley lifetime at room temperature could be significant for future valleytronics applications.