“Core–Shell” Diamond Nanoparticles with NV– Centers and a Highly Isotopically Enriched 13C Shell as a Promising Hyperpolarization Agent

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In this article, we demonstrate the synthesis of “core–shell” diamond nanoparticles, possessing nitrogen–vacancy (NV – ) centers and naturally abundant 13 C in the inner part (or the “core”) and a highly isotopically enriched outer part (or the “shell”). Such nanoparticles are formed by overgrowth over previously electron-irradiated nanodiamonds under high-pressure high-temperature conditions. The synthesized diamond material is investigated using microscopy and spectroscopy techniques. Raman spectroscopy provides an estimate (96%) for the 13 C isotopic content within the “shell”, and the persistence of NV – centers in the natural abundance “core”, providing an optically detected magnetic resonance signal, is confirmed. Considering the measured nuclear polarization lifetime ( T 1 ∼ 90 s), the estimation of the spin diffusion length for the “shell” nuclear spins reveals that 13 C can act as a vector for transferring the spin polarization from NV – centers to the surface. These particles, therefore, offer a promising platform for the hyperpolarization of nuclear spins in a fluid.