SPATIAL CORRELATION OF INFRARED AND PL OPTICAL CENTERS IN HYDROGEN-RICH DIAMONDS

This study gives an analysis of the spatial correlation of absorption features found in the infrared region and photoluminescence (PL) features of several hydrogen-rich diamonds from Zimbabwe. The diamonds were cut into several thin plates and one plate was chosen from each diamond, the largest being approximately 5.0 x 5.0 x 0.3 mm. An ultraviolet laser was used to inscribe axes onto the plates which allowed accurate and consistent maps to be taken. An IR microscope with a mapping functionality was used to analyze the spatial distribution of prominent IR features such as the hydrogen-related 3107 cm^-1 feature and the nitrogen aggregate features at 1170 cm^-1 and 1280 cm^-1. The PL map was taken with 488, 514, and 833 nm lasers and a number of features were tracked. Both maps were taken along a grid with 100 mm spacing covering the majority of the diamond plates.

The plates have noticeable hydrogen clouds with well-defined, symmetrical shapes. The IR mapping shows a very strong correlation of the 3107 cm^-1 peak in the areas with the inclusions. The A-aggregate nitrogen feature at 1280 cm^-1 is inversely correlated with the inclusions. In the PL spectroscopy, the H2 (at 986.2 nm) and H3 (at 503.2 nm) were mapped and correlate with the hydrogen clouds. Several additional peaks at 524, 700.5, 926, and 948 nm also correlate with the clouds. The 637 peak, which is the negatively charged nitrogen-vacancy center [NV^-], shows an inverse correlation.

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