Abstract
Similar electron paramagnetic resonance (EPR) spectra caused by the trigonalcentres NE4 and AB1 have been detected in nitrogen-rich diamond synthesizedwith Ni catalyst by two different groups. The NE4 centre is commonlyconsidered to be the basic structure of several nickel–nitrogen centres that areformed upon the annealing of this type of diamond. However, its EPRspectrum is observed so far only in diamond crystals grown in Novosibirsk,whereas in similar crystals grown in the NIRIM the AB1 centre could bedetected. This discrepancy in the EPR detection could be solved by are-analysis of the published EPR data of the NE4 centre and through EPRinvestigations of synthetic diamonds from Novosibirsk and the NIRIM. Thestudy revealed that the EPR spectrum of the NE4 centre corresponds infact to the spectrum of the trigonal AB1 centre, which is described withS = 1/2 and theg-values g∥ = 2.0027 ± 0.0002 andg⊥ = 2.0923 ± 0.0002.Furthermore, we study whether the experimentalg-valuescan be successfully explained, within the framework of crystal-field theory, by thepreviously proposed models for the AB1 (NE4) centre.
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