Selective measurement of charge dynamics in an ensemble of nitrogen-vacancy centers in nanodiamond and bulk diamond

Abstract

Nitrogen-vacancy (NV) centers in diamond have attracted considerable interest in sensing of weak magnetic fields, such as those created by biological systems. Detecting such feeble signals requires near-surface NV centers, to reduce the distance between NVs and sources. Moreover, dense ensembles of NVs are highly desirable to reduce measurement time. However, robust charge-state switching is often observed in these systems, resulting in a complex interplay between charge and spin dynamics that can reduce the attainable level of spin polarization, and consequently, sensitivity. Understanding the mechanisms behind charge-state switching is, therefore, crucial to developing NV-based sensors. Here, we demonstrate a method to selectively measure charge dynamics in an ensemble of NVs by quenching the spin polarization using an off-axis magnetic field. Utilizing this technique, we show that, in nanodiamonds, charge-state instability increases with increasing NV density. In the case of bulk single crystal diamond, we show that NV centers located near the surface are more stable in the neutral $({\mathrm{NV}}^{0})$ charge state, while the negatively charged $({\mathrm{NV}}^{\ensuremath{-}})$ form is more stable in bulk.