Temperature effects in EPR spectra and optical features of plastically deformed natural IaAB, IaB, and low-nitrogen diamonds

Abstract

In this study, the three natural IaB, IaAB, and low-nitrogen diamond crystals from Yakutian province with plastic deformation characteristic features have been investigated. It is shown that for low-nitrogen and type IaB diamonds, plastic deformation does not lead to brown coloration raising the question about the nature of the color. The crystal of the IaAB type is brown and contains from 53 to 64 % of the total nitrogen in the form of A-aggregates. In electron paramagnetic resonance (EPR), this sample reveals the W7 centers which are formed from the A-centers as a result of plastic deformation and the 490.7 single line related to dangling bonds in the dislocation cores. For this brown plastically deformed diamond the narrowing of the 490.7 EPR line and the dynamical broadening of the W7 lines are observed with a temperature increase from 77 to 300 K. It is assumed that the charge transfer from the W7 defects to dangling bonds in the dislocation core takes place. The obtained changes in the linewidths of EPR spectra can be explained by the mobility of electrons localized on dangling carbon bonds where the varying polarization of the W7 orbitals leads to the modulation of the nitrogen hyperfine structure. In this case, the charge-transfer complexes formed can be responsible for the appearance of the 550 nm band in the optical absorption spectra and, as a consequence, for the brown color of the plastically deformed IaAB diamond sample.