Defects in coloured natural diamonds

Characterization of different types of gem-quality diamonds with UV-VIS-NIR, FTIR and EDXRF spectroscopy reveals a number of optical centers. The colour of the diamonds is clearly caused by a combination of some or all of these centers. Other optically inactive defects can have an effect on the colour of a diamond by influencing the Fermi-level: the relative concentrations of different charged states of a defect in diamond is determined by the Fermi-level. A topographic short-wave UV (225 nm) fluorescence study of growth sector-dependent inclusion of defects in natural diamonds with different colours is also presented. These measurements show that fluorescencent defect centers decorate defect structures connected to growth history of the diamond. On the basis of these characterisation techniques, some interrelationships between different coloured diamonds are highlighted. (C) 2001 Elsevier Science B.V. All rights reserved.