delayed luminescence at from synthetic, silicon-containing samples suggested that the emission originates at $\mathrm{Si}_x\mathrm{N}_y$ or $\mathrm{Si}_x\mathrm{N}_y\mathrm{V}$ complexes [@Wassell2018]. The luminescence is maximized on annealing at and destroyed above [@Wassell2018]. We do not observe this luminescence from any of the present samples at any annealing temperature. Additionally, the annealing behavior of [$\mathrm{SiVN}$]{}is incompatible with the reported annealing behavior of the defect and therefore we conclude that the luminescence does not originate at [$\mathrm{SiVN}$]{}. Furthermore, as [$\mathrm{SiVN}$]{}is the simplest variant of the $\mathrm{Si}_x\mathrm{N}_y\mathrm{V}$ defects, and defect aggregation in diamond typically develops from simple to more complex under higher annealing temperatures, it seems unlikely that the emission originates with any defect in this group.

Conclusion
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The present samples, while dominated in total concentration by nitrogen-related defects, enable additional insight into silicon-related defects and processes which must occur even in lower-concentration samples. The first observation of a doubly-charged defect in diamond leads the way for future studies of other doubly-charged donors or acceptors, provided the ($+$/$2+$) or ($-$/$2-$) levels are sufficiently deep.

The existence of [$\mathrm{SiV}^{2-}$]{} puts limits on the production efficiency of [$\mathrm{SiV}^{-}$]{} qubits in nitrogen-doped material. Previous reports which interpreted the absence of [$\mathrm{SiV}^{-}$]{}in n-type material as the presence of [$\mathrm{SiV}^{0}$]{} 