Creation and microscopic origins of single-photon emitters in transition-metal dichalcogenides and hexagonal boron nitride

We highlight recent advances in the controlled creation of single-photon emitters in van der Waals materials and in the understanding of their atomistic origin. We focus on quantum emitters created in monolayer transition-metal dichalcogenide semiconductors, which provide spectrally sharp single-photon emission at cryogenic temperatures, and the ones in insulating hBN, which provide bright and stable single-photon emission up to room temperature. After introducing the different classes of quantum emitters in terms of band-structure properties, we review the defect creation methods based on electron and ion irradiation as well as local strain engineering and plasma treatments. A main focus of the review is put on discussing the microscopic origin of the quantum emitters as revealed by various experimental platforms, including optical and scanning probe methods.