Color centers in diamond are a promising platform for quantum technologies, and understanding their interactions with the environment is crucial for these applications. We report a study of spin-lattice relaxation $\left(T_1\right)$ of the neutral charge state of the silicon vacancy center in diamond. Above 20 K, $T_1$ decreases rapidly with a temperature-dependence characteristic of an Orbach process and is strongly anisotropic with respect to magnetic-field orientation. As the angle of the magnetic field is rotated relative to the symmetry axis of the defect, $T_1$ is reduced by over three orders of magnitude. The electron spin coherence time $\left(T_2\right)$ follows the same temperature dependence but is drastically shorter than $T_1$. We propose that these observations result from phonon-mediated transitions to a low-lying excited state that are spin conserving when the magnetic field is aligned with the defect axis, and we discuss likely candidates for this excited state.

• Received 10 October 2017
• Revised 28 October 2018

DOI:https://doi.org/10.1103/PhysRevB.98.235140