13C spin-lattice relaxation in nanodiamonds in static and magic angle spinning regimes

We report on C-13 nuclear spin-lattice relaxation time (T-1) dependence on the magic-angle-spinning (MAS) rate in powder nanodiamond samples. We confirm that the relaxation is caused by interaction of nuclear spins with fluctuating electron spins of localized paramagnetic defects. It was found that T-1 is practically not affected by MAS for small particles, while for larger particles with lower defect density T-1 is different in static and MAS regimes and reveals elongation with increasing MAS rate. This effect is attributed to suppression of nuclear spin diffusion by MAS. We propose an approach that describes T-1 dependence on the MAS rate and allows quantitative analysis of this effect. (C) 2014 Elsevier Inc. All rights reserved