Efficient conversion of nitrogen to nitrogen-vacancy centers in diamond particles with high-temperature electron irradiation

Fluorescent nanodiamonds containing negatively-charged nitrogen-vacancy (NV-) centers are promising for a wide range of applications, such as for sensing, as fluorescence biomarkers, or to hyperpolarize nuclear spins. NV- centers are formed from substitutional nitrogen (P1 centers) defects and vacancies in the diamond lattice. Maximizing the concentration of NVs is most beneficial, which justifies the search for methods with a high yield of conversion from P1 to NV-. We report here the characterization of surface cleaned fluorescent micro- and nanodiamonds, obtained by irradiation of commercial diamond powder with high-energy (10 MeV) electrons and simultaneous annealing at 800 degrees C. Using this technique and increasing the irradiation dose, we demonstrate the creation of NV- with up to 25% conversion yield. Finally, we monitor the creation of irradiation-induced spin-1 defects in microdiamond particles, which we associate with W16 and W33 centers, and investigate the effects of irradiation dose and particle size on the coherence time of NV-. (C) 2020 Elsevier Ltd. All rights reserved.