  The silicon vacancy (SiV) center in diamond is drawing much attention due to
its optical and spin properties, attractive for quantum information processing
and sensing. Comparatively little is known, however, about the dynamics
governing SiV charge state interconversion mainly due to challenges associated
with generating, stabilizing, and characterizing all possible charge states,
particularly at room temperature. Here, we use multi-color confocal microscopy
and density functional theory to examine photo-induced SiV recombination - from
neutral, to single-, to double-negatively charged - over a broad spectral
window in chemical-vapor-deposition diamond under ambient conditions. For the
SiV0 to SiV- transition, we find a linear growth of the photo-recombination
rate with laser power at all observed wavelengths, a hallmark of single photon
dynamics. Laser excitation of SiV-, on the other hand, yields only fractional
recombination into SiV2-, a finding we interpret in terms of a photo-activated
electron tunneling process from proximal nitrogen atoms.
