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.