Irradiation Damage in Type I Diamond

Abstract

In addition to the GRI and uv bands induced in all diamond by 0.78‐MeV electron irradiation, another optical absorption feature, which we have named the ND1 band, is found in all Type I diamonds. A single EPR line appears to be associated with the ND1 band. It is suggested that the ND1 center arises from the combination of a defect product—probably an interstitial—and nitrogen in platelet form. Certain observations can only be explained by assuming that the ND1 centers are not distributed randomly through the crystal, but occur in clusters. The ND1 center acts as an acceptor, the center (probably a vacancy) responsible for the GRI and uv band as a donor. In the ionized state, GRI is optically inactive; ND1 is optically active. Electron transfer by thermal excitation results in the bleaching of GRI and enhancement of ND1. Illumination with light in the ND1 band causes electron transfer in the reverse direction, restoring band strengths to their former condition. A model is proposed which defines the energies within the forbidden gap of the ground and excited states of GRI and ND1.