Optimization of NV-Diamond Material Properties for High Sensitivity Magnetometry

Enhancing the sensitivity of ensemble-based magnetometry using NV-diamond requires optimized diamond samples with a high density of negatively-charged NV centers, good fluorescence contrast, and long spin coherence times. Here we report a systematic study of both the conversion efficiency from nitrogen to NV- and the negative-to-neutral NV charge state ratio versus initial nitrogen concentration, irradiation dose, and optical excitation intensity. We present a theoretical model that describes the measured NV charge state dynamics in the presence of both green laser excitation and substitutional nitrogen defects. We correlate a range of characterization measurements, and we draw conclusions on the optimal samples for NV magnetometry, with applications to magnetic surveying, geophysics, and neuroscience.