Effective production of fluorescent nanodiamonds containing negatively-charged nitrogen-vacancy centers by ion irradiation

Fluorescence from negatively-charged nitrogen-vacancy centers (NV(-)s) in diamonds has unique optical properties with none of the undesirable effects such as photo-bleaching and photo-blinking. In addition, the spin-dependent fluorescence intensity of NV(-)s allows us to perform optically detected magnetic resonance (ODMR) investigation for evaluating the presence of NV(-)s and for the electronic local environment. In this work, we irradiated H+, He+, Li+ and N+ ions to nanodiamonds with a median size of 26 nm at various irradiation energies and doses for improving the NV- concentration. ODMR observations of the nanodiamonds showed that ion irradiation increased the number of nanodiamonds containing NV(-)s up to 200 ppm, whereas without ion irradiation, only few NV(-)s were found. The number of nanodiamonds containing NV(-)s at various ion irradiation doses was not monotonous, but had maxima at certain irradiation doses. These results suggest a competition in two opponent roles of vacancies, effective for pairing with nitrogen atoms and as defects for developing damage in crystalline. We also found that sharp and strong ODMR signals were obtained from nanodiamonds irradiated at the optimal condition for the highest yield of NV(-)s. We concluded that He+ ion irradiations with 60 or 80 keV at a dose of 1 x 10(13) ions cm(-2) are the conditions required for the most efficient production of a high quantity of nanodiamonds containing NV(-)s. (C) 2014 Elsevier B.V. All rights reserved.