Paramagnetic centers in detonation nanodiamonds studied by CW and pulse EPR

Dispersed detonation nanodiamonds have been studied by continuous-wave (CW) and pulse EPR techniques. The spectrum of bulk radicals ( g = 2.0025 ± 0.0002, a Lorentz line shape with Δ H pp = 0.95 ± 0.05 mT) dominated in CW EPR and prevented to record spectra from other paramagnetic species. The pulse EPR-spectrum was the superposition of the distorted P1-center spectrum with parameters ( g = 2.0025, A xx = 2.57 mT, A yy = 3.08 mT, A zz = 4.07 mT), the H1-center spectrum ( g = 2.0028) and the single line ( g = 2.0025, Δ H pp = 0.40 ± 0.05 mT) from other centers which may be assigned to surface radicals. The concentration of P1-centers has been estimated by CW EPR as 2 ± 1 ppm N.