  Single photon emitters in hexagonal boron nitride have gathered a lot of
attention due to their favourable emission properties and the manifold of
possible applications. Despite extensive scientific effort, the exact atomic
origin of these emitters has remained unkown thus far. Recently, several
studies have tied the emission in the yellow spectral region to carbon-related
defects, but the exact atomic structure of the defects remains elusive. In this
study, photoluminescence emission and excitation spectroscopy is performed on a
large number of emitters within this region. By comparison of the experimental
data with theoretical predictions, the origin of yellow single photon emission
in hexagonal boron nitride is determined. Knowledge of this atomic structure
and its optical properties is crucial for the reliable implementation of these
emitters in quantum technologies.
