given in [@DHaenens-Johansson2011]: in the heated state the concentration of both charge states is below and therefore all [$\mathrm{SiV}$]{}defects are in the $2-$ charge state, requiring of donor charges between the two states. The corresponding loss in [$\mathrm{N_{s}^{0}}$]{} from UV to heated states is , more than accounting for the [$\mathrm{SiV}$]{}-related charge effects. This relationship is true at all annealing temperatures. As a result, the changes in donor concentrations cannot be attributed solely to [$\mathrm{SiV}$]{}and it is therefore difficult to quantify the latent [$\mathrm{SiV}^{2-}$]{} concentration in the UV state. Upper limits can be estimated based on the assumption that the only donor is [$\mathrm{N_{s}^{0}}$]{}; however, this is known not to be the case in these samples (e.g. [${\ensuremath{\mathrm{NVH}}\xspace}^{-}$]{}, other photochromic peaks in \[Fig \[fig:ir\_comparison\]\]).

The extremal charge states are unstable at room temperature in all of the present samples. Time-lapse absorption measurements of [$\mathrm{SiV}^{-}$]{}, performed in the absence of ambient light, show that after UV treatment of [Sample F]{}the concentration of [$\mathrm{SiV}^{-}$]{} increases by approximately over . Ambient light increases the rate of this change, and significant color changes are visible after in ambient. The changes cannot be described by a simple coupled model with constant leakage rates from ${\ensuremath{\mathrm{SiV}^{0}}\xspace}{}\rightarrow{\ensuremath{\mathrm{SiV}^{-}}\xspace}{}$ 