  Shallow negatively charged silicon-vacancy centers have applications in
magnetic quantum sensing and other quantum applications. Vacancy centers near
the surface (within 100 nm) have different spin relaxation rates and optical
spin polarization, affecting the optically detected magnetic resonance (ODMR)
signal. This makes it essential to characterize these centers. Here we present
the relevant spin properties of such centers. ODMR with a contrast of up to 6
%, which is better than the state of the art, allowed us to determine the zero
field splitting, which is relevant for most sensing applications. We also
present intensity-correlation data to verify that the signal originates from a
single center and to extract transition rates between different electronic
states.
