Spectroscopic signatures of interfacial energy transfer in MoS2-based van der Waals heterostructures under deep-UV excitation.

We report a comprehensive photoluminescence (PL) and photoluminescence excitation (PLE) study of monolayer MoS2 and its van der Waals heterostructures with hBN and graphene under deep-ultraviolet (DUV) excitation. Using synchrotron-based VUV/UV spectroscopy, we reveal that while pristine MoS2 exhibits only A-exciton emission at ∼660 nm under visible excitation, broadband near-infrared emission (750-900 nm) emerges at cryogenic temperatures under DUV excitation in MoS2/hBN and MoS2/graphene heterostructures. This emission indicates a nonlocal excitation-emission mechanism facilitated by interfacial energy transfer from the UV-absorbing layers. In MoS2/hBN, a broad UV band near 350 nm also appears under 200 nm excitation and is attributed to impurity-related defect luminescence in hBN. The interfacial processes are governed by temperature-sensitive radiative channels involving defect-bound states or localized excitons in MoS2. Our results highlight the crucial role of interlayer coupling and spectral sensitization in enabling new radiative pathways in 2D heterostructures, offering novel strategies for tailoring light emission in layered optoelectronic systems.