Spin S=1 centers: A universal type of paramagnetic defects in nanodiamonds of dynamic synthesis

Intrinsic paramagnetic defects in 5nm sized nanodiamonds, produced by various dynamic synthesis (DySND) techniques (detonation, shock-wave, pulsed laser ablation of solid carbon containing targets), have been studied by multi-frequency electron paramagnetic resonance (EPR). X-band (910GHz) EPR spectra of DySND, in addition to the main intensive singlet Lorentzian-like EPR signal, reveal a low intensity doublet pattern within the half-field (HF) region (g4). On transferring spectra to the Q-band (34GHz) the shape of the HF pattern changes and splitting between doublet components is reduced from 10.4 to 2.6mT. The HF patterns observed are attributed to the forbidden ΔM _S=2 transitions between the Zeeman levels of some spin-triplet (S=1) centers. The model of two triplet centers with g2.003 and zero-field splitting parameters D ₁=0.095cm ¹ (TR1) and D ₂=0.030cm ¹ (TR2) satisfactorily describes experimental results at both microwave frequencies. The spin-triplet-type defects are observed in a wide variety of DySND samples irrespective of industrial supplier, cooling and carbon soot refinement methods, initial purity, disintegration, or subsequent targeted chemical modification. This indicates that the intrinsic defects with S=1 in DySND systems are of universal origin.