Rapid determination of single substitutional nitrogen Ns concentration in diamond from UV-Vis spectroscopy

Single substitutional nitrogen atoms ${\mathrm{N}}_s^0$ are the prerequisite to create nitrogen-vacancy (NV) centers in diamonds. They not only serve as the electron donors to create the desired NV⁻ center and provide charge stability against photo-ionisation but also are the main source of decoherence. Therefore, precise and quick determination of ${\mathrm{N}}_s^0$ 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 ${\mathrm{N}}_s^0$ 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 ${\mathrm{N}}_s^0$ 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 ${\mathrm{N}}_s^0$ concentrations in a single crystal. A cross-check with electron paramagnetic resonance shows high reliability of our method and yields the absorption cross section of the 270 nm absorption band $\sigma =1.96\pm 0.15$ cm⁻¹ ppm⁻¹ (in common logarithm) or ${\sigma }_e=4.51\pm 0.35$ cm⁻¹ ppm⁻¹ (in natural logarithm), which serves as a reference to determine ${\mathrm{N}}_s^0$ concentrations and makes our method applicable for others without the need for a known ${\mathrm{N}}_s^0$ -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 ${\mathrm{N}}_s^0$ concentrations.