Ultrafast Spectroscopy Studies Of WSe₂/MoTe₂ Type ?Van Der Waals Heterostructures

Two-dimensional(2D)transition-metal dichalcogenides(TMDs)have shown great potential in ultrathin and flexible optoelectronic and photonics devices.Besides emissive bright excitons,they also possess rich non-emissive dark excitons including momentum-forbidden indirect excitons and spin-forbidden triplet-like excitons,which could be dominant species under optical or electrical excitation in 2D optoelectronic and photonic devices.Efficient harvesting of both bright and dark excitons from TMDs and understanding the exciton transfer mechanism consequently are not only fundamental interest but also a technological challenge.Here,by combining steady-state photoluminescence spectroscopy and ultrafast transient reflectance spectroscopy,we show efficient exciton harvesting by ultrafast energy transfer in WSe2/MoTe2 van der Waals heterostructures,leading to the photoluminescence enhancement of MoTe2.The energy transfer occurs with near-unity yield and in an ultrafast(?200 fs)manner for both bright and dark excitons,suggesting a dominant Dexter-type energy-transfer process consisting of simultaneous transfer of both electron and hole in van der Waals coupled 2D layers at ultimate proximity.This result is beyond the conventional dipole-dipole coupling mechanism typically assumed at 2D interfaces and offers a path to high speed and enhanced light harvesting and emission applications based on 2D heterostructures.At the same time,the excellent optical and electrical properties of 2D TMDs are sensitive to the external dielectric environment,so we are interested in the research on the regulation of monolayer TMDs optical properties by the constructing a simple exciton field.By combining steady-state reflectance spectroscopy and ultrafast transient reflectance spectroscopy,we found WSe2/MoTe2 type ? van der Waals heterostructures which have a unique electronic band structure configuration can build a simple exciton electric field outside WSe2 with 1030nm exciting,by inducing the exciton binding energy changing to achieve regulation of WSe2 related optical properties.This research rich the diversity of regulating the 2D TMDs optical property methods,lead us to have a preliminary understanding for the influence of mechanism about the exciton electric field regulating the 2D semiconductor material photoelectric properties and it also promotes the further development of related optoelectronic equipment application.