  Observation of interlayer, charge-transfer (CT) excitons in van der Waals
heterostructures (vdWHs) based on 2D-2D systems has been well investigated.
While conceptually interesting, these charge transfer excitons are highly
delocalized and spatially localizing them requires twisting layers at very
specific angles. This issue of localizing the CT excitons can be overcome via
making mixed dimensional vdWHs (MDHs) where one of the components is a
spatially quantum confined medium. Here, we demonstrate the formation of CT
excitons in a 2D/quasi-2D system comprising MoSe2 and WSe2 monolayers and
CdSe/CdS based core/shell nanoplates (NPLs). Spectral signatures of CT excitons
in our MDHs were resolved locally at the 2D/single-NPL heterointerface using
tip-enhanced photoluminescence (TEPL) at room temperature. By varying both the
2D material, the shell thickness of the NPLs, and applying out-of-plane
electric field, the exciton resonance energy was tuned by up to 120 meV. Our
finding is a significant step towards the realization of highly tunable
MDH-based next generation photonic devices.
