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Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

We report on EPR and 13C and 1H NMR studies of detonation nanodiamond particles with surface grafted by paramagnetic gadolinium ions obtained by ion exchange with hydrogen atoms of carboxyl groups through the reaction of aqueous nanodiamond suspension with an aqueous solution of gadolinium nitrate. Our findings give clear evidence that Gd3+ ions are chemically bound to the nanodiamond surface and interact with electron and nuclear spins of the diamond nanoparticle, which results in acceleration of electron and nuclear spin–lattice relaxations. A model of positioning of Gd3+ ions on the DND surface terminated by oxygen-containing groups is suggested. The distance between the Gd ion and nanodiamond surface is estimated by relaxation measurements as 0.32 nm. Biomedical applications of the studied nanomaterials are discussed.

We report on a 1H NMR study of diamond nanoparticles decorated by copper and cobalt. Increase in the 1H relaxation rate under decoration results from the interactions of hydrogen nuclear spins of the surface hydrocarbon and hydroxyl groups with paramagnetic copper and cobalt ions. This finding reveals the appearance of paramagnetic Cu2+ or Co2+ ions on the detonation nanodiamond (DND) surface rather than as a separate phase, which is consistent with the 13C NMR data of the same samples. Our results shed light on the mechanism of ion incorporation. A topological model for relative position of paramagnetic Cu2+ or Co2+ ions and hydrogen atoms on the DND surface is suggested. An application of the studied nanomaterials in the field of biomedicine is discussed.