and ${\ensuremath{\mathrm{SiV}^{-}}\xspace}{}\rightarrow{\ensuremath{\mathrm{SiV}^{2-}}\xspace}{}$. Instead, the increase is well-described by a hyperbolic function, as expected by multiple overlapping thermal processes. This is consistent with the present material containing multiple thermally-activated donors/acceptors at room temperature.

The existence of [$\mathrm{SiV}^{2-}$]{} casts doubt on the optical absorption cross-section for [$\mathrm{SiV}^{-}$]{}given in [@DHaenens-Johansson2011]. The cross-section for [$\mathrm{SiV}^{0}$]{} was calibrated by directly measuring its concentration by EPR and equating it to the absorption strength measured by UV-Vis. However, the cross-section for [$\mathrm{SiV}^{-}$]{} was calibrated via charge transfer between [$\mathrm{SiV}^{0}$]{} and [$\mathrm{SiV}^{-}$]{} using the protocol given in §\[subsec:charge\_transfer\]: the loss of the former was equated to the gain in the latter. The assumption was that only two charge states were involved in the process: any loss or gain of population to or from [$\mathrm{SiV}^{2-}$]{} was unaccounted for, and would result in a modified absorption cross-section than the one given in [@DHaenens-Johansson2011]. The concentrations of [$\mathrm{SiV}^{-}$]{} given by the cross-section are within approximately a factor of two of the expected concentration based on charge balance arguments. However, the high concentration of [$\mathrm{SiV}^{2-}$]{} in these samples makes a more precise statement impossible at this time. A future study based on intrinsic or even p-type material should bias between [$\mathrm{SiV}^{-}$]{} and 