Electron spin resonance spectra, which were designated W26 and W25, were observed in type-Ia samples. This showed that the H3 and H4 optical absorptions, respectively, were due to excited states of the defects which were responsible for these absorptions. Zero-field and hyperfine parameters were determined. Previously proposed models for the H4/W25 defect and, by implication, for the B nitrogen aggregate were confirmed. Electron spin resonance data also supported a previously proposed model for the H3 center.

J.A.Van Wyk, G.S.Woods: Journal of Physics - Condensed Matter, 1995, 7[29], 5901-11