Utilizing EPR spectroscopy to determine the structure of nitrogen impurities in diamonds

Treated color diamonds are becoming increasingly abundant in the gem diamonds industry. In addition to traditional/conventional gemological gem diamond evaluation methods, it is carried out also by UV-visible and Infra-Red spectroscopy, Raman and cathodoluminescence spectroscopy.

In this study, electron paramagnetic resonance (EPR) spectroscopy is used to determine the structure of the dispersed nitrogen atoms in treated fancy (colored) diamonds. The colors examined were blue, pink, yellow, orange (cognac) and green. The EPR basic principle relays on determinations of atoms with an unpaired electron, radicals. It is a very sensitive method and capable of measuring concentrations as low as radicals/cc. The nitrogen content is determined by Infra-Red spectroscopy.

The results indicate that all the carbon radicals observed are affected by adjacent nitrogen atoms and have a fine hyperfine structure of the nitrogen (splitting the nitrogen signal accordingly). The highest concentration of radicals and hyperfine structures is observed in pink and orange treated diamonds.