The vacancy as a probe of the strain in type IIa diamonds

The width of the vacancy related photoluminescence from diamond is used to qualitatively measure the strain in type IIa diamonds of a range of brown colours and to measure the effect on the strain of high pressure high temperature annealing of the brown diamonds. The results indicate that for untreated type IIa diamonds the strain in colourless diamonds is generally less than that observed in brown ones. Annealing to remove the brown colour brings about a measurable reduction in the strain as assessed via the luminescence line width; but a dependence on the depth of the original brown colour is retained with the value remaining in most cases above 1.70 meV, a width below which 92% of the untreated colourless diamonds lie.