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The nitrogen-vacancy center in diamond attracts a lot of attention in sensing applications, mainly for temperature, magnetic field, and rotation measurements. Nuclear spins of carbon-13 surrounding the nitrogen-vacancy center can be used as a memory or sensing element. In the current work, a diamond plate with a relatively large concentration of carbon-13 was synthesized and examined. The spectrum of optically detected magnetic resonance was recorded and analyzed in a magnetic field range of 5-200 G. A strain-independent measurement technique of carbon-13 isotope concentration based on the analysis of magnetic resonance spectra was developed. Additionally, narrow features in the spectrum were detected and understood.

The nitrogen-vacancy color center in diamond is one of the most important systems in the fast-growing field of sensing. This color centers are used in both high-resolution and high-sensitivity sensors. However, techniques for quick and efficient formations of this color center are still in the development stage. In this paper, we present a study on the influence of the electron irradiation dose on the conversion of substitutional nitrogen into $\text{N}{{\text{V}}^{-}}$ centers. The study was done on diamonds that were highly enriched with nitrogen (~100 ppm), which on one hand should maximize the effect of irradiation, and on another be of interest for high-sensitivity magnetometers. The maximum achieved conversion efficiency was as high as ${37\pm 3.7}$, with no observed saturation on the electron dose even with the simplest annealing procedure. The measurements of the corresponding dephasing time made it possible to estimate for shot-noise limited sensitivity per unit volume of a stationary field sensor with such a diamond to be ${9\pm 1\times {{10}^{-14}}\text{T}}/{\sqrt{\text{Hz}\cdot \text{m}{{\text{m}}^{-3}}}}\;$.

The sensitivity of the nitrogen-vacancy (NV) color centers in diamond-based magnetometers strongly depends on the number of NV centers involved in the measurement. Unfortunately, an increasing concentration of NV centers leads to decreases of their dephasing and coherence time if the nitrogen content exceeds a certain threshold level (approximately ${10^{17}}{\rm{ c}}{{\rm{m}}^{ - 3}}$). Here, we demonstrate that this increased dephasing can be efficiently compensated by postprocessing procedures in the vicinity of the threshold concertation, thus extending possible useful concentrations on NV centers with the maximum possible decoherence time in diamonds with a natural carbon content.

The sensitivity of magnetic and electric field sensors based on nitrogen-vacancy (NV) center in diamond strongly depends on the available concentration of NV and their coherence properties. Achieving high coherence times simultaneously with high concentration is a challenging experimental task. Here, we demonstrate that by using a high-pressure, high-temperature growing technique, one can achieve nearly maximally possible effective coherence T2* times, limited only by carbon nuclear spins at low nitrogen concentrations or nitrogen electron spin at high nitrogen concentrations. Hahn-echo T2 coherence times were also investigated and found to demonstrate reasonable values. Thus, the high-pressure, high-temperature technique is a strong contender to the popular chemical vapor deposition method in the development of high-sensitivity, diamond-based sensors.

We report a magnetic field dependence of fluorescence of diamond single crystals containing NV$^-$ centers. In such spectra, numerous sharp lines are found, which correspond to Level Anti-Crossings (LACs) in coupled spins systems comprising an NV$^-$ center. Theoretical modeling of such "LAC-spectra" enables characterization of paramagnetic defect centers and determination of their magnetic resonance parameters, such as zero-field splitting and hyperfine coupling constants. The outlined method thus enables sensitive detection of paramagnetic impurities in diamond crystals., Comment: 12 pages, 14 figures

The dependence of the luminescence of diamonds with negatively charged nitrogen-vacancy centers (NV-) vs. applied magnetic field (magnetic spectrum) was studied. A narrow line in zero magnetic field was discovered. The properties of this line are considerably different from those of other narrow magnetic spectrum lines. Its magnitude is weakly dependent of the orientation of the single-crystal sample to the external magnetic field. This line is also observed in a powdered sample. The shape of the line changes greatly when excitation light polarization is varied. The magnitude of the line has a non-linear relation to excitation light intensity. For low intensities this dependence is close to a square law. To explain the mechanism giving rise to this line in the magnetic spectrum, we suggest a model based on the dipole-dipole interaction between different NV- centers., Comment: 8 pages, 6 figures