  Low-temperature scanning tunneling microscopy is used to probe, with
atomic-scale spatial resolution, the intrinsic luminescence of a van der Waals
heterostructure, made of a transition metal dichalcogenide monolayer stacked
onto a few-layer graphene flake supported by an Au(111) substrate. Sharp
emission lines arising from neutral, charged and localised excitons are
reported. Their intensities and emission energies vary as a function of the
nanoscale environment of the van der Waals heterostructure, explaining the
variability of the emission properties observed with diffraction-limited
approaches. Our work paves the way towards understanding and control of
optoelectronic phenomena in moir\'e superlattices with atomic-scale resolution.
