Enhanced Optical <sup>13</sup> C Hyperpolarization in Diamond Treated by High‐Temperature Rapid Thermal Annealing
Max Gierth, Valentin Krespach, Alexander I. Shames, Priyanka Raghavan, Emanuel Druga, Nicholas Nunn, Marco D. Torelli, Ruhee Nirodi, Susan Le, Richard L. Zhao, Alessandra Aguilar, Xudong Lv, M. Shen, Carlos A. Meriles, Jeffrey A. Reimer, A.M. Zaitsev, Alexander Pines, Olga Shenderova, Ashok Ajoy
Abstract
Abstract Methods of optical dynamic nuclear polarization open the door to the replenishable hyperpolarization of nuclear spins, boosting their nuclear magnetic resonance/imaging signatures by orders of magnitude. Nanodiamond powder rich in negatively charged nitrogen vacancy defect centers has recently emerged as one such promising platform, wherein 13 C nuclei can be hyperpolarized through the optically pumped defects completely at room temperature. Given the compelling possibility of relaying this 13 C polarization to nuclei in external liquids, there is an urgent need for the engineered production of highly “hyperpolarizable” diamond particles. Here, a systematic study of various material dimensions affecting optical 13 C hyperpolarization in diamond particles is reported on. It is discovered surprisingly that diamond annealing at elevated temperatures ∼1720 °C has remarkable effects on the hyperpolarization levels enhancing them by above an order of magnitude over materials annealed through conventional means. It is demonstrated these gains arise from a simultaneous improvement in NV − electron relaxation/coherence times, as well as the reduction of paramagnetic content, and an increase in 13 C relaxation lifetimes. This work suggests methods for the guided materials production of fluorescent, 13 C hyperpolarized, nanodiamonds and pathways for their use as multimodal (optical and magnetic resonance) imaging and hyperpolarization agents.