Ultraviolet Quantum Emitters in Hexagonal Boron Nitride from Carbon Clusters

Ultraviolet (UV) quantum emitters
in hexagonal boron nitride (hBN)
have generated considerable interest due to their outstanding optical
response. Recent experiments have identified a carbon impurity as
a possible source of UV single-photon emission. Here, on the basis
of first-principles calculations, we systematically evaluate the ability
of substitutional carbon defects to develop the UV color centers in
hBN. Of 17 defect configurations under consideration, we particularly
emphasize the carbon ring defect (6C), for which the calculated zero-phonon
line agrees well the experimental 4.1 eV emission signal. We also
compare the optical properties of 6C with those of other relevant
defects, thereby outlining the key differences in the emission mechanism.
Our findings provide new insights into the strong response of this
color center to external perturbations and pave the way to a robust
identification of the particular carbon substitutional defects by
spectroscopic methods.