Ultraviolet Quantum Emitters in Hexagonal Boron Nitride fromCarbon Clusters

Ultraviolet (UV) quantum emitters in hexagonal boron nitride (hBN) havegenerated considerable interest due to their outstanding optical response. Recent experimentshave identified a carbon impurity as a possible source of UV single-photon emission. Here, onthe basis offirst-principles calculations, we systematically evaluate the ability of substitutionalcarbon defects to develop the UV color centers in hBN. Of 17 defect configurations underconsideration, we particularly emphasize the carbon ring defect (6C), for which the calculatedzero-phonon line agrees well the experimental 4.1 eV emission signal. We also compare theoptical properties of 6C with those of other relevant defects, thereby outlining the keydifferences in the emission mechanism. Ourfindings provide new insights into the strongresponse of this color center to external perturbations and pave the way to a robustidentification of the particular carbon substitutional defects by spectroscopic methods