Role of extended defects in brown colouration of diamond

Abstract

AbstractThe absorption spectrum of brown diamond is broad and featureless, in both natural type IIa and CVD‐grown material. It is argued that such an absorption is due to an extended, rather than a point, defect. Ab‐initio modelling studies have been conducted on dislocations and extended vacancy‐related defects. While certain dislocations could potentially explain the origin of colour, their density is too low to account for experimentally observed absorption magnitudes. It is demonstrated that a vacancy disk lying in the {111} plane has an absorption spectrum similar to that seen in natural and CVD brown diamond. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)