High NV Density in a Pink CVD Diamond Grown with N2O Addition

Growing high-purity diamond containing dense negatively charged nitrogen-vacancy (NV-) centre ensembles is desirable for the development of sensitive quantum sensors that explore the coherent manipulation of the spin states of this atomic-scale defect. By using N2O as a dopant, we demonstrate that millimetre-thick single crystals can be grown by Chemical Vapour Deposition (CVD) with substitutional nitrogen concentrations as high as 26 ppm. With a high-energy electron irradiation treatment and in-situ annealing, up to 20% of this nitrogen can be successfully converted into NV- centres leading to densities of almost 5 ppm and to a crystal displaying pink colouration and appealing optical properties. The longitudinal relaxation T-1 time in such a highly doped diamond is measured to be around 3.5 ms at 300 K while inhomogeneous dephasing time T-2* is estimated to 600 ns. Despite the high NV density, Electron Spin Resonance lines are resolved with clear hyperfine splitting induced by the nuclear spin of nitrogen. The dependence of T-1 on the orientation of the magnetic field suggests that relaxation is dominated by NV-NV dipole interactions when no magnetic field is applied. Such engineered crystals constitute a promising platform for developing future quantum sensing applications. (C) 2020 Elsevier Ltd. All rights reserved.