SiV defects. Here, the neutral and negatively charged SiV defects possess two and one hole, respectively [@Gali2013]. In replacing one of the neighboring carbon atoms with nitrogen the number of holes present in the defect must decrease by one: we thus expect the positive, neutral and negative charge states to possess 2 ($S=0$ or 1), 1 ($S=1/2$), and zero ($S=0$) holes respectively, and we identify the new spectrum with [$\mathrm{SiVN}^0$]{}. Charge transfer measurements on all samples are consistent with this description. The EPR spectrum is photochromic, with the concentration changing from approximately to between the UV and heat-treated charge states in [Sample F]{}: the behavior of the defect is therefore qualitatively similar to the behavior of [$\mathrm{SiV}^{0}$]{}. In the heated sample state, we observe no additional EPR spectra and deduce the dominant charge state is [$\mathrm{SiVN}^-$]{}, which is $S=0$ in its ground state and therefore EPR-inactive.

[ l l p[0.5cm]{} S\[retain-explicit-plus,table-format=8.8\] l S\[retain-explicit-plus,table-format=+1.1\] S\[retain-explicit-plus,table-format=8.8\] l S\[retain-explicit-plus,table-format=+1.1\] S\[retain-explicit-plus,table-format=8.8\] l S\[retain-explicit-plus,table-format=+1.1\] ]{}

Parameter & Unit && & && & & & &\
$g$ & 1 & Exp. & 2.00472+-0.00005 & $\hkl[001]$ & +4.3 & 2.00549+-0.00005 & $\hkl[110]$ & +4.3 & 2.00288+-0.00005 & $\hkl[1-10]$\
& & Exp. & -3.800+-0.01 & $\hkl[111]$ & +2.7 