Feature Gems & Gemology, Fall 2005, Volume 41, No. 3

Experimental CVD Synthetic Diamonds from LIMHP-CNRS, France

In the last decade, progress in diamond growth by chemical vapor deposition (CVD) has resulted in significant improvement in the quality of synthetic single crystals. This article reports on the gemological and spectroscopic features of six synthetic type IIa diamonds grown for research purposes at the French Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions (LIMHP-CNRS), and compares their diagnostic features to CVD-grown diamonds from other producers. Three of the six samples were nitrogen doped, whereas the other three were classified as high purity. A number of characteristics that are diagnostic of CVD synthetic diamond were present in the nitrogen-doped crystals, despite an absence of defect-related absorption features in the infrared region. Identification of the high-purity samples was more complicated, but it was still possible based on features in their photoluminescence spectra, their distinctive birefringence, and characteristic luminescence images.