  Topological defects, such as Stone-Wales defects and grain boundaries, are
common in 2D materials. In this study, we investigate the intricate interplay
of topological defects and carbon contamination in hexagonal boron nitride
revealing an intriguing class of color centers. We demonstrate that both carbon
contamination and strain can stabilize Stone-Wales configurations and give rise
to emitters with desirable optical properties in the visible spectral range.
Inspired by these results, we further demonstrate that carbon atoms at grain
boundaries can resolve energetic B-B and N-N bonds leading to highly favorable
atomic structures that may facilitate the accumulation of carbon contamination
at the boundaries. Similarly to contaminated Stone-Wales defects, carbon-doped
grain boundaries can also give rise to color centers emitting in the visible
spectral range with short radiative lifetime and high Debye-Waller factors. Our
discoveries shed light on an exciting class of defects and pave the way toward
the identification of color centers and single photon emitters in hBN.
