Optically active point defects in high quality single crystal diamond
We use density functional theory to investigate the optical properties of vacancy di-nitrogen, vacancy-nitrogen-hydrogen and vacancy di-hydrogen defects. The first is a common defect found in irradiated natural type IaA diamonds while the second is found in as-grown CVD diamond. The last has not yet been detected. We find that these defects possess at least two charge states which can lead to photochromic behaviour. In the neutral and negative states, the three defects have optical bands due to internal transitions and two weaker optical absorption bands coming from charge state changes. Thus at least four absorption bands are expected for these defects. Vibrational modes of the hydrogen defects are reported.