  The recently discovered negatively charged tin-vacancy centre in diamond is a
promising candidate for applications in quantum information processing (QIP).
We here present a detailed spectroscopic study encompassing single photon
emission and polarisation properties, the temperature dependence of emission
spectra as well as a detailed analysis of the phonon sideband and Debye-Waller
factor. Using photoluminescence excitation spectroscopy (PLE) we probe an
energetically higher lying excited state and prove fully lifetime limited
linewidths of single emitters at cryogenic temperatures. For these emitters we
also investigate the stability of the charge state under resonant excitation.
These results provide a detailed insight into the spectroscopic properties of
the $\text{SnV}^-$ centre and lay the foundation for further studies regarding
its suitability in QIP.
