Study On The Dynamics And Upconversion Luminescence Properties Of MoSe₂ Monolayer And Its Heterostructure

Starting with the discovery of graphene in 2004,across many disciplines,the exceptional electrical,chemical,thermal,and optical properties of 2D materials have drawn considerable attention that has created a new field in the more than ten years after their discovery.At present,molybdenum selenide in transition metal sulfide is the least studied material compared with other materials.It is of great significance to explore the dynamic process and potential application of molybdenum selenide and its van der Waals heterostructures for enriching the research content and expanding the development of the subject.We designed and fabricated the sample by the mechanical exfoliation technique,studied the dynamics and luminescent process of MoSe₂monolayer and its van der Waals heterostructure.Here we fabricated a MoSe₂ monolayer partially covered with a hexagonal boron nitride flake and changed the local dielectric environment to control the exciton transport in 2D semiconductors.This provides a new solution for room temperature operations and exciton transport control of exciton devices.In the measurement of the sample,the dynamic process of exciton was studies by photoluminescence measurements and spatiotemporally resolved differential reflection measurements.The rigid displacement model is constructed by matlab and a theoretical simulation method is proposed to describe the transport process of excitons.The quantitative fitting results at the junction between the two regions revealed that the excitons moved across the junction for about 50 ps over a distance of about 200 nm,which defines exactly the order of magnitude for speed of exciton transport.These results show that exciton transport in a MoSe₂ monolayer semiconductor can be effectively controlled by van der Waals dielectric screening,which contribute to understanding the effects of the dielectric environment on the electronic and optical properties of two-dimensional semiconductors.Here we designed skillfully a MoSe₂/WS₂/MoS₂ trilayer van der Waals heterostructures composed of monolayer of three materials,and observed the upconversion photoluminescence phenomenon for the first time.Using a MoSe₂/WS₂/MoS₂ trilayer as an example,we show that by exciting the MoSe₂ and MoS₂ layers with a low-energy 670-nm laser beam,photoluminescence of 620 nm can be obtained.The upconversion photoluminescence originates from the transfer of electrons and holes from MoSe₂ and MoS₂,respectively,to the middle WS₂ layer,where they recombine.The results illustrate an unexplored physical mechanism for upconversion photoluminescence in van der Waals heterostructures and provide a certain foundation for their application in optoelectronic applications.