HIGH TEMPERATURE ANNEALING OF HYDROGEN-RICH DIAMONDS

This study gives an analysis of the effect of high temperature annealing on the infrared and photoluminescence (PL) features as well as the inclusions of two hydrogen-rich diamond plates from Zimbabwe that were cut from the same rough. The samples showed strong inclusion-related zoning known as hydrogen clouds which consist of micron-sized particles of as yet undetermined structure. This allowed hydrogen-rich and hydrogen-poor areas to be compared throughout the annealing study.

The diamond plates were annealed to temperatures of 300^oC, 600^oC, 800^oC, 1000^oC, 1400^oC, and 1700^oC. The infrared and PL, and Raman maps were collected after every temperature step to study the effects of heat on the defects, and photomicrographs were collected to study the inclusions.

Several photoluminescence features were seen to decrease in size including the 637 nm peak, which is the negatively charged nitrogen-vacancy center [NV^-] and the 503.2 nm peak, known as the H3 and consists of two nitrogen atoms and vacancy in the neutral charge state and normally has a high thermal stability. The H2 defect at 986.2 nm, which is the negative form of the H3, was shown to increase after annealing. The hydrogen clouds underwent dramatic changes in apparent color and particle size, going from a light translucent gray appearance to an opaque black. The particle size grew from less than one micron to an average of fourteen microns, and the hexagonal outline of the particles became noticeable. Spatial raman spectroscopy was used to show that the color change and size change were due to graphitization of the included particles.