HRD Antwerp reported on 28 September 2015 that they had received a 3.09-carat CVD (chemical vapour deposition) synthetic diamond for examination recently, the largest of its kind encountered by the lab. The lab-grown diamond is a slightly tinted white (I to J), VS2, brilliant cut stone with measurements of 9.36 – 9.42mm x 5.76mm and no fluorescence (nil).
The lab employed D-screen and Alpha Diamond Analyser for screening and both instruments indicated that the stone require further testing. As the latter device confirmed that it was a type IIa diamond, it showed that it is potentially grown in laboratory or HPHT treated. The diamond went through various spectroscopic analyses subsequently. With the help of DiamondView Imaging, a layered growth structure, which is characteristic of CVD diamonds, is found at the pavilion of the stone. Based on this the lab assumed that the stone was grown in different steps rather than in a single run. The table of the stone displayed a ‘somewhat cloud-like structure’. While visual examination did not reveal fluorescence, DiamondView Imaging showed a red and purple fluorescence. No phosphorescence was observed.
UV-VIS absorption spectroscopy and Photoluminescence laser spectroscopy were performed for further characterisation. One of the major features that can be detected in CVD diamonds is the SiV- centre doublet around 737 nm. While the presence of SiV- centre is only weakly detected by UV-VIS absorption spectroscopy (Figure 4, left), its presence is stronger with PL laser spectroscopy (Figure 4, right). Except for the NV0 centre, no other peaks are observed in the UV-VIS spectrum. There are no clear indications of possible colour treatment after growth.
HRD Antwerp concluded that in view of the layered growth procedure of the CVD method, a very large plate must have been created in order to be able to cut a 3.09ct brilliant shaped diamond out of it. ‘Whereas previously only smaller diamonds were created by chemical vapour deposition, it now seems to be no obstacle any more to create cut diamonds of up to 3 carats,’ said the article.
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