MAGI Application note:

Detecting synthetic CVD-diamond with GemmoRaman-532SG™

Jan. 8. 2014 Mikko Åström, Alberto Scarani, Marco Torelli

Synthetic diamonds grown by CVD-method (Chemical Vapor Deposition) have recently gained a lot of publicity in jewelry trade publications and triggered many alerts about undisclosed stones submitted to major gemological laboratories. Development of pure CVD- diamond production has been fast and dynamic because the material has great potential for semiconductor industry. Detecting CVD-diamonds polished as gems  has become extremely difficult if not impossible to deal with by using traditional gemological tools.

CVD synthetic diamonds currently on the market can be unambigously identified only by combination of two advanced test methods; UV-fluorescence microscopy and photoluminescence spectroscopy. UV-fluorescence microscope (such as DeBeers DiamondView) is used for revealing curved growth striations of CVD-diamond also known as "terraces" (Fig 1.) Extended range and enhanced signal to noise ratio of scientific grade GemmoRaman-532SG™ spectrometer addresses the latter requirement by detecting subtle photoluminescense peaks arising from silicon impurity in these diamonds.

While silicon impurities have been found from very limited set of natural samples, it is still considered as very strong indication of CVD- origin of a diamond. The crystallographic SiV--defect, consisting of negatively charged Silicon atom next to a vacancy (a missing carbon atom) is very stable and can not be removed in commercial HPHT- treatment temperatures.

In some CVD-stones it is also possible to detect SiV-peak by UV-Vis-NIR spectroscopy, but many scientific studies have shown that its sensitivity is not sufficient enough in all cases. Therefore, for studying CVD diamonds, the more sensitive PL-spectroscopy technique is preferred.



Fig1. Curved growth striations of CVD-diamond photographed with MAGI in-house build deep ultraviolet (<225nm) fluorescence microscope. 15x, Marco Torrelli

References & Further reading

CVD Synthetic Diamonds from Gemesis Corp, Gems & Gemology, Summer 2012, vol. 48
Wuyi Wang, Ulrika F. S. D’Haenens-Johansson, Paul Johnson, Kyaw Soe Moe, Erica Emerson, Mark E. Newton, and Thomas M. Moses

Identification of Synthetic Diamond Grown Using Chemical Vapor Deposition (CVD) Gems & Gemology, Spring 2004, vol. 42
Philip M. Martineau, Simon C. Lawson, Andy J. Taylor, Samantha J. Quinn, and David J. F. Evans, and Michael J. Crowder

New Generation of Synthetic Diamonds Reaches the Market (Part A):  CVD-grown Blue Diamonds
Contributions to Gemology, Nov 2013, No. 14, p.1-14
Adolf Peretti, Franz Herzog, Willy Bieri, Matthias Alessandri, Detlef Günther, Daniel A. Frick, Ed Cleveland, Alexandre M. Zaitsev, Branko Deljanin