Things we still don't know about optical centres in diamond

In this article the optical spectra associated with some of the major defects in diamond are considered. In particular, we deal with isolated substitutional boron, isolated substitutional nitrogen and the nitrogen aggregates, the self-interstitial and defect complexes involving the self-interstitial with nitrogen or boron. Although some aspects of the spectra are understood, many puzzles and inconsistencies remain. The absorption bands responsible for the colours of natural pink and amber diamonds are discussed and studies of transition metal complexes in high-pressure high-temperature synthetic diamond are briefly mentioned. (C) 1999 Elsevier Science S.A. All rights reserved.