Exciton Radiative Recombination Dynamics and Nonradiative Energy Transfer in Two-Dimensional Transition-Metal Dichalcogenides

We employ fluorescence lifetime imaging technology to explore exciton radiative recombination dynamics in layered transition-metal dichalcogenides (TMDCs) and nonradiative energy transfer from CdSe/ZnS quantum dot (QD) to monolayer TMDCs (MoS2, WS2, and WSe2). Owing to an indirect direct band gap transition, exciton radiative lifetimes decrease with the TMDCs' layer number reducing. The fastest exciton recombination rate is observed in monolayer TMDCs, which is attributed to their reduced dielectric screening. Furthermore, the effect of reduced dielectric screening on nonradiative energy transfer from QDs to monolayer TMDCs is investigated. The fastest energy transfer rate is observed in QD/WS2 heterostructure owing to weak dielectric screening of monolayer WS2, and the slowest rate in QDs/MoS2 is caused by strong dielectric screening of monolayer MoS2. Our experiments provide fundamental insights into exciton recombination dynamics in TMDCs and potentially enable new avenues for controlling motion of excitonic energy conversion on a nanoscale.