Hydrothermal Growth of Nanodiamonds for Quantum Applications

Abstract For decades, pyrolysis of organic compounds has been pursued to produce graphitic carbon, revealing that structural evolution depends more on reaction dynamics than precursor chemistry. Here, a parallel and previously overlooked pathway is uncovered: the spontaneous formation of nanodiamonds (NDs) at temperatures as low as 220 °C and 2.5 MPa during the earliest stages of carbonization. These transient sp 3 clusters, long masked by amorphous carbon, can now be unambiguously identified through the activation of optically addressable nitrogen vacancy (NV − ) and silicon vacancy (SiV − ) centers, supported by Raman spectroscopy of 1321 nm and high‐resolution transmission electron microscopy (HRTEM) lattice spacings of 0.206 nm consistent with diamond. The resulting NDs exhibit robust quantum‐optical signatures, including Optically detected magnetic resonance (ODMR) with a contrast of ≈16%, comparable to values measured in bulk single‐crystal diamond, confirming the formation of quantum‐grade color centers within these sub‐10 nm NDs. This discovery reshapes the understanding of carbon phase evolution and establishes a sustainable, solution‐processed pathway for scalable, low‐temperature synthesis of quantum‐relevant NDs, a capability once thought exclusive to nature or extreme synthesis conditions.