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

Intrinsic paramagnetic defects in ∼5 nm 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 (9-10 GHz) 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 (g ∼ 4). On transferring spectra to the Q-band (34 GHz) the shape of the HF pattern changes and splitting between doublet components is reduced from 10.4 to 2.6 mT. 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 g ∼ 2.003 and zero-field splitting parameters D(1) = 0.095 cm(-1) (TR1) and D(2) = 0.030 cm(-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.