INFRARED-ABSORPTION BY THE B-NITROGEN AGGREGATE IN DIAMOND

Two approaches have been adopted in attempting to determine the streng th of the one-phonon infrared absorption by the B nitrogen aggregate i n diamond. On the one hand, we have heat treated purely type IaA speci mens with known infrared absorption strengths (and thus also known nit rogen concentrations) to bring about partial aggregation of the A cent res to B centres, monitoring changes in the strengths of the A, and re sultant B, one-phonon components by decomposition of the ensuing infra red spectra. Secondly, we have made direct chemical assays of nitrogen in diamonds that show dominant B absorption features. This approach i s complicated because diamonds in which the B aggregate is the only po int defect also contain extended defects that may or may not involve n itrogen. These defects may or may not, in turn, contribute to absorpti on in the one-phonon region. Nevertheless, the nitrogen concentrations have been measured for two distinct groups of diamonds that both uncr itically might at first glance be typed together as 'IaB'. By taking i nto account subtle differences between the infrared spectra of these g roups, and making allowance for what is known from electron microscopi cal observations about their defect contents, it is possible, despite certain experimental indeterminacies, to arrive at a reasonably consis tent interpretation of the measurements. A value of 794 +/- 8 at.ppm/c m(-1) is suggested for the absorption strength, at 1282 wavenumbers, o f the B nitrogen aggregate.