  Silicon carbide with optically and magnetically active point defects offers
unique opportunities for quantum technology applications. Since interaction
with these defects commonly happens through optical excitation and
de-excitation, a complete understanding of their light-matter interaction in
general and optical signatures, in particular, is crucial. Here, we employ
quantum mechanical density functional theory calculations to investigate the
photoluminescence lineshapes of selected, experimentally observed color centers
(including single vacancies, double vacancies, and vacancy impurity pairs) in
4H-SiC. The analysis of zero-phonon lines as well as Huang-Rhys and
Debye-Waller factors are accompanied by a detailed study of the underlying
lattice vibrations. We show that the defect lineshapes are governed by strong
coupling to bulk phonons at lower energies and localized vibrational modes at
higher energies. Generally, good agreement to the available experimental data
is obtained, and thus we expect our theoretical work to be beneficial for the
identification of defect signatures in the photoluminescence spectra and
thereby advance the research in quantum photonics and quantum information
processing.
