Atomically resolved exciton emission from single defects in MoS₂

Excitons, bound electron-hole pairs, govern the optical response of semiconductors and underpin technologies ranging from photovoltaics to quantum light sources. In nanoscale systems, the spatial extent of excitons approaches atomic dimensions, yet direct imaging of excitonic processes in real space has remained elusive. Two-dimensional semiconductors such as transition metal dichalcogenides provide a platform where reduced screening, high light extraction and atomically defined defect sites enable the exploration of exciton physics at atomic length scales. However, the microscopic origin of defect-related emission and its variability across samples have remained debated. Here we show that scanning tunnelling microscopy-induced luminescence reveals the atomic and optical fingerprints of individual defects in monolayer MoS₂. Decoupling the material from its substrate using bilayer hexagonal boron nitride enables the detection of sharp excitonic emission and spatially localized defect emission, which we attribute to free-to-bound recombination (e,A⁰), and map its distribution with subnanometre-resolved fluorescence imaging. We identify negatively charged carbon-hydrogen complexes as the defect species responsible for a ubiquitous defect emission band in MoS₂. These results provide atomically resolved images of exciton emission in a solid-state material, linking atomic defect structure to its optical fingerprint and establishing a microscopic basis for deterministic quantum emitter engineering in two-dimensional materials.