Rapid determination of single substitutional nitrogen N$_s^0$ concentration in diamond from UV-Vis spectroscopy

TL;DR

This paper introduces a rapid, simple UV-Vis spectroscopy method to accurately determine single substitutional nitrogen concentrations in diamonds, offering advantages over traditional techniques in speed, sensitivity, and local measurement capability.

Contribution

The authors develop and validate a UV-Vis absorption spectroscopy technique for N$_s^0$ quantification, including a reliable absorption cross section, enabling widespread, calibration-free application.

Findings

High correlation with EPR measurements

Effective for low and varying concentrations

Applicable for local and bulk analysis

Abstract

Single substitutional nitrogen atoms N$_s^0$ are the prerequisite to create nitrogen-vacancy (NV) centers in diamonds. They serve as the electron donors to create the desired NV$^-$ center, provide charge stability against photo-ionisation, but also are the main source of decoherence. Therefore, precise and quick determination of N$_s^0$ concentration is a key advantage to a multitude of NV-related research in terms of material improvement as well as applications. Here we present a method to determine the N$_s^0$ concentration based on absorption spectroscopy in the UV-Visible range and fitting the 270 nm absorption band. UV-Visible spectroscopy has experimental simplicity and widespread availability that bear advantages over established methods. It allows a rapid determination of N$_s^0$ densities, even for large numbers of samples. Our method shows further advantages in determining low concentrations as well as the ability to measure locally, which is highly relevant for diamonds with largely varying N$_s^0$ concentrations in a single crystal. A cross-check with electron paramagnetic resonance (EPR) shows high reliability of our method and yields the absorption cross section of the 270~nm absorption band, $\sigma=1.96\pm0.15$ cm$^{-1}\cdot$ppm$^{-1}$ (in common logarithm) or $\sigma_e=4.51\pm0.35$ cm$^{-1}\cdot$ppm$^{-1}$ (in natural logarithm), which serves as a reference to determine N$_s^0$ concentrations, and makes our method applicable for others without the need for a known N$_s^0$-reference sample and calibration. We provide a rapid, practical and replicable pathway that is independent of the machine used and can be widely implemented as a standard characterization method for the determination of N$_s^0$ concentrations.