Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered increasing attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN via various bottom-up synthesis methods and directly through ion implantation, we provide direct evidence that the visible SPEs are carbon related. Room-temperature optically detected magnetic resonance is demonstrated on ensembles of these defects. We perform ion-implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of the simplest 12 carbon-containing defect species suggest the negatively charged \({\rm{V}}_{\rm{B}}{\rm{C}}_{\rm{N}}^ -\) defect as a viable candidate and predict that out-of-plane deformations make the defect environmentally sensitive. Our results resolve a long-standing debate about the origin of single emitters at the visible range in hBN and will be key to the deterministic engineering of these defects for quantum photonic devices.

六方氮化硼（hBN）中的单光子发射器（SPE）由于其卓越的光学性能，在过去几年中受到越来越多的关注。然而，尽管有大量的实验结果和理论计算，但仍存在难以捉摸的缺陷结构。在这里，通过各种自下而上的合成方法并直接通过离子注入，控制杂质向hBN中的掺入，我们提供了直接的证据证明可见的SPE与碳有关。在这些缺陷的集合体上证明了室温光学检测的磁共振。我们进行离子注入实验，并确认只有碳注入才能在可见光谱范围内产生SPE。\（{\ rm {V}} _ {\ rm {B}} {\ rm {C}} _​​ {\ rm {N}} ^-\）缺陷是可行的候选者，并预测面外变形使缺陷对环境敏感。我们的结果解决了关于hBN可见光范围内单个发射器起源的长期争论，这将是对量子光子器件中这些缺陷进行确定性工程设计的关键。