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

TL;DR

This study investigates increasing negatively charged nitrogen-vacancy center density in nanodiamonds derived from nitrogen-rich type Ib diamonds, revealing a nearly linear relationship up to a certain nitrogen concentration, with implications for brighter fluorescent nanodiamonds.

Contribution

It demonstrates a method to enhance NV- center density in nanodiamonds from nitrogen-rich diamonds and analyzes the effects of nitrogen content and crystallinity on fluorescence properties.

Findings

NV- density increases nearly linearly with nitrogen content up to 200 ppm.

Higher nitrogen content (>200 ppm) leads to reduced fluorescence due to impurities.

Crystallinity affects the efficiency of NV- formation and fluorescence brightness.

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 materials. The nanodiamonds (10 - 100 nm in diameters) were prepared by ball-milling of microdiamonds, in which the density of neutral and automatically dispersed nitrogen atoms [N0] was measured by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). A systematic measurement for the fluorescence intensities and lifetimes of the crushed monocrystalline diamonds as a function of [N0] indicated that the [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 (FNDs) are discussed.