(color online) (a) Photoluminescence image of isolated defect QDs in WSe₂. The dashed triangle indicates the position of the monolayer WSe₂ (left). Photoluminescence spectrum of localized emitters (middle). The emission of the localized emitters exhibits much sharper spectral lines (the linewidths of the two spectra are ∼ 112 and 122 μeV, respectively. left inset) than that of free excitons (∼ 10 meV, right inset). Second-order correlation measurements revealed a strong photon antibunching (right).^[100] (b) WSe₂ emission spectra as a function of applied gate voltage, corresponding to light emission from quantum dot-like defects (left). Magnetic field dependence of a quantum dot emission spectra in the Faraday configuration (right).^[102] (c) Fluorescence saturation curve obtained from a single defect in hBN multilayers. Scanning confocal image of a multilayer hBN sample (inset).^[104]