Enhanced activation yield of nitrogen-vacancy and silicon-vacancy diamond color centers by proton and carbon irradiation

We investigate the activation yield and optical properties of the negatively charged nitrogen-vacancy (NV -) and silicon-vacancy (SiV -) centers in single-crystal diamonds, focusing on the effect of proton (p) and carbon-ion (C) irradiation on their formation. The samples, either nitrogen-rich or silicon-implanted, are grown by chemical vapor deposition or high pressure-high temperature synthesis. They are irradiated over three orders of magnitude in fluence, up to ∼1014C/cm2 or ∼ 1016 p/cm2, generating up to ∼104 ppm of extra vacancies at the end-of-range. Following thermal annealing at 1150 °C for 1 h, we characterize the samples using time-resolved spectroscopy, optical spectroscopy, and optically detected magnetic resonance. The optical properties of the NV - and SiV− centers remain stable even at vacancy concentrations of ∼103-104 ppm. At the same time, the activation yield of substitutional nitrogen and (primarily) interstitial silicon increases significantly with vacancy density, from below 2 % to approximately 15–20 % for both centers. A statistical model of defect dynamics during annealing accounts for these results, showing that the activation yield follows a logarithmic dependence on local vacancy concentration - extending over three decades for NV - and two for SiV -.