Infrared absorption by the single nitrogen and A defect centres in diamond

Abstract The infrared absorption spectra of a suite of twenty-one type Ib synthetic diamonds have been recorded, and the concentrations of nitrogen in the form of single substitutional N atoms in these specimens determined by electron spin resonance measurements. It is found that an absorption coefficient, at 1130 wave-numbers, of 1 cm−1 is produced by 250 ±2at. p.p.m. of nitrogen in this form, a. result identical to that of Chrenko, Strong and Tuft and consistent also with that of Woods, van Wyk and Collins. Seventeen of these specimens were heated at temperatures between 1800 and 2050°C, under a stabilizing pressure, to bring about an appreciable degree of aggregation of the single N defects into A centres, or nitrogen pairs. For each specimen the residual, unaggregated single N defect concentration was then determined by electron spin resonance. The difference between this and the original value gave the concentration of nitrogen in the form of A defects. The infrared absorption strength of the A centres was obtained in each case by decomposition of the infrared spectrum into the residual single N, and A, components. In this way it is found that the absorption coefficient at 1282 wavenumbers due to A centres is 1 cm−1 per 16.2±1 at. p.p.m. This value is in good agreement with an earlier result obtained by inert-gas fusion and the result given in the paper that immediately follows.