The understanding and controlled creation of atomic defects in semiconductor transition metal dichalcogenides (TMDs) are highly relevant to their applications in high-performance quantum optics and nanoelectronic devices. Here, we demonstrate a versatile approach in generating single-photon emitters in MoS2 monolayers using widely attainable UV light. We discover that only defects engendered by UV photons in vacuum exhibit single-photon-emitter characteristics, whereas those created in air lack quantum emission attributes. In combination with theoretical calculations, we assign the defects generated in vacuum to unpassivated sulfur vacancies, whose highly localized midgap states give rise to single-photon emission. In contrast, UV irradiation of the MoS2 monolayers in air results in oxygen-passivated sulfur vacancies, whose optical properties are likely governed by their pristine band-to-defect band optical transitions. These findings suggest that widely available light sources such as UV light can be utilized for creating quantum photon sources in TMDs.
Keywords: UV irradiation; oxygen-passivated defect; quantum defect; single-photon emitter; sulfur vacancy; transition metal dichalcogenides.