The link between brown colour and vacancy structures in natural diamond and was studied through the techniques of aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy. Bright field and high angle annular dark field imaging modes revealed discrete patches of stronger contrast, of the order of 1nm in size, that were similar to simulated images of vacancy clusters. Core loss spectra show a pre-edge feature for brown diamond corresponding to π* states. This feature was absent for colourless and heat treated brown diamonds. Additional spectra acquired in regions containing dislocations for both brown and white (colourless) diamonds showed a second pre-edge feature indicating that dislocations have electronic states associated with them and were therefore optically active.

An Analysis of Vacancy Clusters and sp2 Bonding in Natural Type IIa Diamond using Aberration Corrected STEM and EELS. I.S.Godfrey, U.Bangert: Journal of Physics - Conference Series, 2011, 281[1], 012024