Two approaches were used in an attempt to determine the strength of the 1-phonon infra-red absorption by B-type N aggregates. In one case, purely type-IaA specimens with known infra-red absorption strengths (and therefore known N concentrations) were heat-treated so as to cause partial aggregation of A-type centers to B-type centers. Changes in the strengths of the A-type, and resultant B-type, 1-phonon components were monitored via the decomposition of the resultant infra-red spectra. In the other case, direct chemical analyses were made of the N in diamonds which exhibited predominantly B-type absorption features. This approach was complicated because the diamonds in which the B-type aggregate was the only point defect also contained extended defects that could involve N. These defects could, in turn, contribute to absorption in the 1-phonon region. The N concentrations were measured for 2 distinct groups of diamonds that could both be mistaken for IaB. By taking account of subtle differences between the infra-red spectra of these groups, and by making allowances for data concerning their defect contents which had been obtained from electron microscopic observations, it was possible to arrive at a reasonably consistent interpretation of the measurements. A value of 79.4ppm[at]cm was suggested for the absorption strength, at 1282 wave-numbers, of the B-type N aggregate.

S.R.Boyd, I.Kiflawi, G.S.Woods: Philosophical Magazine B, 1995, 72[3], 351-61