High Pressure High Temperature Synthesized Diamond Particles with Controlled Nitrogen Content

Diamond particles hosting nitrogen vacancy centers is a platform material for potential use in emerging nano and microscale sensing technologies. These envisioned quantum sensors are based on optical manipulation and readout of NV centers in response to external environmental stimuli (e.g., temperature, electromagnetic fields, mechanical strain). The important prerequisites for such measurement protocols are NV centers with suitable spin properties such as long coherence and relaxation times. While such properties are observed in bulk diamond crystals of suitable quality, the properties of diamond particles are often severely degraded by the presence of paramagnetic defects such as electronic spins associated with surface defects and other paramagnetic centers (primarily nitrogen P1 centers). Here we demonstrate HPHT grown microparticulate diamond with good crystal quality and a controlled nitrogen content in the range of <i>ca.</i> 5-50 atomic ppm. A resultant improvement in NV electronic spin coherence times by approximately 3-fold is directly observed by pulsed electron paramagnetic resonance (EPR) across the range of nitrogen concentration studied. These results may provide a foundation for the production of the next generation of fluorescent diamond particles, which thus far have relied exclusively on particulate diamond with nitrogen contents of ca. 100 atomic ppm.