---
abstract: 'We report the first experimental observation of a doubly-charged defect in diamond, [$\mathrm{SiV}^{2-}$]{}, in silicon and nitrogen co-doped samples. We measure spectroscopic signatures we attribute to substitutional silicon in diamond, and identify a silicon-vacancy complex decorated with a nearest-neighbor nitrogen, [$\mathrm{SiVN}$]{}, supported by theoretical calculations. Samples containing silicon and nitrogen are shown to be heavily photochromic, with the dominant visible changes due to the loss of $\mathrm{SiV^{0/-}}$ and gain in the optically-inactive [$\mathrm{SiV}^{2-}$]{}.'
author:
- B G Breeze
- C J Meara
- X X Wu
- C P Michaels
- R Gupta
- P L Diggle
- M W Dale
- B L Cann
- T Ardon
- 'U F S D’Haenens-Johansson'
- I Friel
- M J Rayson
- P R Briddon
- J P Goss
- M E Newton
- B L Green
title: 'Doubly-charged silicon vacancy center, photochromism, and Si-N complexes in co-doped diamond'
---

Introduction
============

Diamond, as with other wide-band-gap semiconductors, has recently attracted attention as a host for optically-active point defects with potential applications in quantum communication [@Atature2018], nanophotonics [@Aharonovich2014; @Schroder2016], and quantum information processing (QIP) [@Awschalom2018]. In addition to the well-known nitrogen-vacancy (NV, where V denotes a vacancy henceforth) [@Doherty2013], 