Creation of high density ensembles of nitrogen-vacancy centers in nitrogen-rich type Ib nanodiamonds

Abstract

This work explores the possibility of increasing the density of negatively charged nitrogen-vacancy centers ([NV−]) in nanodiamonds using nitrogen-rich type Ib diamond powders as the starting material. The nanodiamonds (10–100 nm in diameter) were prepared by ball milling of microdiamonds, in which the density of neutral and atomically dispersed nitrogen atoms ([N0]) was measured by diffuse reflectance infrared Fourier transform spectroscopy. A systematic measurement of the fluorescence intensities and lifetimes of the crushed monocrystalline diamonds as a function of [N0] indicated that [NV−] increases nearly linearly with [N0] at 100–200 ppm. The trend, however, failed to continue for nanodiamonds with higher [N0] (up to 390 ppm) but poorer crystallinity. We attribute the result to a combined effect of fluorescence quenching as well as the lower conversion efficiency of vacancies to NV− due to the presence of more impurities and defects in these as-grown diamond crystallites. The principles and practice of fabricating brighter and smaller fluorescent nanodiamonds are discussed.