# Selective measurement of charge dynamics in an ensemble of nitrogen-vacancy centers in nano- and bulk diamonds

## TL;DR

This paper introduces a new method to selectively measure charge dynamics in NV centers within diamonds, revealing how charge stability varies with NV density and location, which is vital for improving quantum sensing applications.

## Contribution

A novel technique using off-axis magnetic fields to isolate charge dynamics in NV ensembles, enhancing understanding of charge stability in nanodiamonds and bulk diamonds.

## Key findings

- Charge instability increases with NV density in nanodiamonds.
- Surface NVs are more stable in the neutral charge state.
- Bulk NVs favor the negatively charged state.

## 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 novel 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 (NV$^{0}$) charge state, while the negatively charged (NV$^{-}$) form is more stable in bulk.