Defect-Induced Single-Photon Emission in ZnPS₃

Research on single photon sources in layered materials has been limited so far to transition metal dichalcogenides (TMDs) and hexagonal boron nitride (hBN) as hosting platforms. These quantum emitters exhibit advantages due to the distinct semiconducting and insulating characteristics of the two classes of materials, which enable their integration with van der Waals heterostructures and devices. Here, we report single photon emission in ZnPS₃, which belongs to the MPX₃ family characterized by stronger electronic correlations than those observed intrinsically in TMDs or hBN. We provide a comprehensive characterization of the vibrational and optical properties of nonmagnetic ZnPS₃ crystals, focusing on unraveling the mechanisms responsible for the single photon emission. Using polarization-resolved Raman scattering spectroscopy, we identify key phonon modes and uncover strong metal-ligand interactions that influence both phonon dynamics and defect-bound excitonic states. Low-temperature photoluminescence spectroscopy reveals stable and narrow optical transitions localized at defect sites, while second-order correlation measurements confirm the quantum nature of the emission. We complement our experimental analysis with ab initio density functional and GW many-body perturbation theory calculations to investigate the characteristics of the bulk and defect-related electronic structure. Our theoretical analysis reveals that phosphorus vacancies introduce midgap states, enabling optical transitions occurring at the energy range consistent with the experimentally observed emission lines. This joint approach identifies P-vacancies as the likely origin of single photon emitters in ZnPS₃. Furthermore, we anticipate that similar behavior should be present in other MPX₃ compounds, offering a framework for exploring defect-based quantum emitters with intrinsic magnetic tunability.