Point defects in crystalline solids behave as optically addressable individual quantum systems when present in sufficiently low concentrations. In two-dimensional (2D) semiconductors, such quantum defects hold potential as versatile single photon sources. Here, we report the synthesis and optical properties of Nb-doped monolayer WS₂ in the dilute limit where the average spacing between individual dopants exceeds the optical diffraction limit, allowing the emission spectrum to be studied at the single-dopant level. We show that these individual dopants exhibit common features of quantum emitters, including narrow emission lines (with linewidths <1 meV), strong spatial confinement, and photon antibunching. These emitters consistently occur within a narrow spectral range across multiple samples, distinct from common quantum emitters in van der Waals (vdW) materials that show large ensemble broadening. Analysis of the Zeeman splitting reveals that they can be attributed to bound exciton complexes comprising dark excitons and negatively charged Nb.

当以足够低的浓度存在时，晶体固体中的点缺陷表现为光学可寻址的单个量子系统。在二维 （2D） 半导体中，这种量子缺陷具有作为多功能单光子源的潜力。在这里，我们报告了 Nb 掺杂单层 WS₂ 在稀释极限下的合成和光学特性，其中单个掺杂剂之间的平均间距超过光学衍射极限，从而可以在单掺杂剂水平上研究发射光谱。我们表明，这些单独的掺杂剂表现出量子发射器的共同特征，包括窄发射线（线宽为 <1 meV）、强空间限制和光子反聚束。这些发射器始终出现在多个样品的狭窄光谱范围内，这与范德华 （vdW） 材料中表现出大系综展宽的常见量子发射器不同。对塞曼分裂的分析表明，它们可归因于由暗激子和带负电荷的 Nb 组成的结合激子复合物。