THE NITROGEN-CONTENT OF TYPE IA NATURAL DIAMONDS

The nitrogen concentrations of type Ia diamonds have been measured, by inert gas fusion analysis, as a function of their infrared absorption strengths. With purely type IaA diamonds it is found that an absorption coefficient of 1 cm-1 is produced, at 1282 wavenumbers, by 17.5 at. ppm of nitrogen. This result is consistent, through experiments in which single N atoms have been made to aggregate to form A defects (nitrogen pairs), with measurements relating the strength of the infrared absorption to the concentration of single N atoms. For purely type IaB diamonds we find that an absorption coefficient of 1 cm-1 is produced, again at 1282 wavenumbers, by 103.8 at. ppm of nitrogen. This figure is in excellent agreement with the results of an earlier photon activation analysis of such diamonds. However, pure type IaB diamonds are expected to contain voidites, which themselves contain nitrogen. Possible reasons which could account for the observed linearity between the total measured nitrogen and the absorption due to the B defects are considered. © 1990.