NDT breaking the 10 carat barrier – world record synthetic diamonds investigated
The first small manufactured industrial diamonds were produced in 1953 by the Swedish company ASEA but their accomplishment went unannounced. In 1970, General Electric (GE) produced synthetic diamond crystals using the HPHT method with a belt type of press and created a 0.78ct polished RBC colorless diamond. In the 1980’s and 1990’s Russians used their own technology (“BARS” and “TOROID” high pressure apparatus (HPA) with high pressure presses of up to 25 MN load) to grow industrial and crystals up to 2.00ct in polished size, mostly orange to yellow in colour. In the last 15 years, companies including Lucent, Chatham, AOTC, Gemesis (now IIa Technologies) and many other producers in China, Germany, India, Russia, Ukraine, USA and Taiwan have improved the technology yet again and used their expertise to successfully grow diamond crystals that cut to 1.00ct up to 2.00ct in size. This “next generation” of diamonds exhibited high clarities (VS and VVS) and colours (D-H), as well as new blue and pink colours (after irradiation). Other companies (ref. 2-3) including Scio Diamonds, Washington Diamonds, Taidiam, PDC diamonds and Pure Grown Diamonds(selling arm of IIa technologies) are also using a very different technology/process of Chemical Vapour Deposition (CVD) to produce laboratory-grown diamonds up to 3.00 ct in size (table 1).
Production Facility and Technology
The new world record for the largest laboratory-grown diamond crystal is 60ct and this gem was produced during the first week of July 2015 at the New Diamond Technology (NDT) facility in St. Petersburg (Russia) during an inspection by Branko Deljanin (CGL-GRS). In April 2015, NDT experimentally produced a 32.26ct colorless gem quality diamond crystal. From this stone, the largest lab-grown faceted diamond in the world has been cut. It is a 10.02ct faceted square emerald-cut synthetic diamond (Fig. 4a and Fig. 10). The NDT facility in St. Petersburg has over 50 HPHT presses (incl. 25MN load presses equipped with a high pressure apparatus (HPA) type “TOROID” and 50MN load presses type SK850 equipped with HPA type “Cubic”, see Fig. 1 and Fig. 2a), producing 5,000ct of diamonds per month in collaboration with a modern cutting facility (Fig. 2b and Fig. 3a) where they process and polish the laboratory-grown diamonds. New Diamond Technology Ltd recently entered the synthetic diamond jewellery market after completing eight years of research and successful production of type IIa and IIb crystal plates for specific industrial applications (medical, synchrotron radiation and anvil design). NDT now uses much larger cubic type presses (the latest 850 series, Chinese made), and as a result many large stones can be produced in one run (16 colorless stones, 6-10 cts rough) in a cycle that takes 10 to 12 days on average.
World synthetic diamond production volume from 2014-2017 is unlikely to be more than 2.5 million carats (white crystals) per year, and lab-grown diamonds currently represent only 2.5 – 3.0% of the natural diamond supply. This could change dramatically (double or triple) in the next 1 or 2 years if the Chinese manufacturers move their focus from the production of industrial diamond powder to growing single crystal diamonds and adapt their technologies to produce large crystals using cubic HPHT presses (Fig. 1).
Material and Methods
Six of the largest crystals and polished colorless diamonds, including the record breaking 10.02ct (E VS1), 5.11ct (I, SI1) and 4.30ct (D, VS2) were tested at the M&A Gemological Instruments facility in Finland by M. Åström and B. Deljanin, and six other samples (including 2 blue lab-grown diamonds) were tested at the GRS laboratory in Hong Kong by M. Alesandri and Dr. A.Peretti. Both examinations used standard instruments and advanced spectrometers.
The instruments used at M&A Gemological Instruments facility were:
- GemmoRaman-532SG Raman/Photoluminescence spectrometer (536 – 765nm, 0.25nm resolution, TEC-cooled CCD)
- GemmoFtir fourier transform infrared spectrometer (tested with resolution 4cm -1 , range 500-7000cm -1)
- GemmoSphere UV-Vis-NIR spectrometer
- MAGI in-house built deep ultraviolet fluorescence excitation setup with 200nm, 258nm, 360nm and broadband UV- filtering
The instruments used at GRS laboratory in Hong Kong were:
- A custom-built UV-VIS-NIR instrument using a quadruple-channel Czerny-Turner spectrometer and two broadband light sources recorded the spectra in the wavelength range from 240 – 1100 nm. This apparatus enabled the detection at liquid-nitrogen temperature (LNT) of very weak absorptions with spectral resolution better than 0.2 nm.
- Photoluminescence (PL) of all samples was analyzed at LNT using a custom-built spectrometer working with 405 nm and 532 nm excitation lasers. PL measurements were performed in a wavelength range from 408 to 1100 nm range (UV-VIS-NIR and PL equipment assembled by Dr. Thomas Hainschwang, GGTL Laboratories).
- Infrared absorption spectra were recorded in the mid-IR range from 400 – 7800 cm-1 (resolution 4 cm-1) at room temperature using a Perkin Elmer Spectrum Two FTIR spectrometer equipped with a ZnSe beam splitter.
- An ED-XRF instrument (FISCHERSCOPE XANDPP) was used to examine the trace elements within the diamonds.
Examination with Microscope and Polarized Light
Most NDT-grown diamonds studied exhibit high (Fig. 4a) to medium (Fig. 3b) clarity (VVS1-SI1). Based on this clarity, for the majority of stones it is not possible to distinguish them from similarly colored natural diamonds by using just a loupe or microscope. Only a few lower clarity stones (especially crystals) had metallic inclusions that are typical for HPHT grown diamonds (Ref. 7). As expected, none of the samples exhibited any pattern when examined under cross polarized filters. This is likely due to a relatively short growth period (Ref. 6).
UV Fluorescence and Phosphorescence
As found with other HPHT-grown diamonds on the market, the SWUV (254nm) fluorescence of NDT-grown diamonds were greenish blue and stronger than LWUV (365nm) in half of the samples (Ref. 7). An interesting new feature discovered in approximately half of the samples is a weak-medium bluish orange fluorescence and phosphorescence (Fig. 3c and Fig. 5). This phenomena were not only present when excited by UV lamp but also when exposed to a strong pinpoint light (e.g. LED light). These samples were part of NDT’s latest production.
All colorless lab-grown diamonds tested were type IIa with no presence of nitrogen and a small amount of boron (Fig. 6). Two blue lab-grown diamonds (Fig. 7a) were type IIb (Fig. 7b). They contained boron in higher amounts than found in natural type IIb blue diamonds (Ref. 5).
Research tests at the GRS facility in Hong Kong confirmed preliminary results (Fig. 8a and Fig. 8b) by analysing additional 6 samples with repeated measurements and under various measuring conditions (no Ni-related peaks were found). All samples investigated by GRS remain in their reference collection for further investigation. Additional spectroscopic information was collected from these lab-grown diamonds, exhibiting unusual fluorescence and phosphorescence behaviour (Fig. 7b).
NV0 (575nm) and NV-(637nm) and Si-V0 (737nm) centres are present in approximately half of the samples. Si-V0 defect is found in CVD-grown diamonds and are extremely rare in natural diamonds and rare in HPHT-grown diamonds. Nickel was not detected in our samples and if is present, then it is probably present at low concentration below sensitivity of our PL spectrometers (using 405nm and 532nm lasers at GRS or 532nm laser at M&A Gemological Instruments). Further research is required to determine if NV centres (Fig. 8a) in NDT-grown diamonds are the result of additional HPHT treatment (used historically by other companies to improve the color of natural and synthetic diamonds) or is caused by some other phenomenon.
In our opinion, the orange color luminescence is most probably caused by NV centres, eventually in combination with other defects. This is most likely a characteristic of the very large stones and is caused by the long lasting growth period when stones were exposed to high pressures and temperatures.
The only detected element in all samples was iron (Fe). Titanium (Ti) was only detected in samples where the seed is still exposed. We did not detect any manganese (Mn), cobalt (Co) or nickel (Ni) that are traditionally used as catalysts in the HPHT process. This can be explained because most of the samples tested were of high clarity (VS2 and better) and therefore without metallic inclusions.
Diamonds grown by New Diamond Technology (NDT) are the largest colorless synthetic diamonds reported to date (Fig. 10), with weights up to 60ct crystals and 10.02 ct faceted (Fig. 9). Most samples are of high color grades (colorless and near-colorless, D-J) and high to medium clarity, but may contain metallic inclusions formed from metal/catalyst. Natural and CVD synthetic diamonds show strong Ia or weak IIa birefringence patterns as they are more heavily strained than HPHT synthetic diamonds. HPHT synthetic diamonds do not show birefringence under cross polarized filters (Ref. 6 and 7). Our colorless samples were type IIa with some boron (weak type IIb) or blue with high B content. Their natural counterparts, colorless type IIa diamonds are highly transparent and considered the worlds most valuable diamonds, usually appearing in large sizes (5ct – 100ct+) and in high colors (D-E) and clarities (IF-VVS). They are also known as type “Golconda” diamonds because legendary the “best” stones are historically believed to originate from the Golconda province in India. All synthetic diamonds fluoresced and phosphoresced blue under SWUV light. In addition, half of them showed orange color when exposed to a UV lamp, with stronger responses to short-wave than long-wave excitation and lasting phosphorescence. Natural diamonds show a stronger reaction (usually blue) under LWUV than SWUV light. Phosphorescence in natural diamonds is very rare and almost exclusively found in type IIb and Chameleon diamonds, but without blue/orange colour. Therefore the synthetic diamonds can be distinguished based on their phosphorescence, particularly from their natural type IIa counterparts.
Photoluminescence spectra revealed NV centres and in combination with other defects could be responsible for orange luminescence. Boron impurities are responsible for the blue phosphorescence in HPHT-grown diamonds but further research is needed to determine what is causing the orange phosphorescence. The exact nature of the phosphorescence processes is still not fully understood, but likely involves complex steps of charge carrier trapping and de-trapping (Ref. 5). Orange phosphorescence could come from the recombination at donor-acceptor pair. In case of NDT-grown diamonds with orange phosphorescence, the donor may be the NV center or some others. Further research is underway to also understand role of boron and other impurities present.
Using a combination of standard gemological and spectroscopic tests, it is possible to identify all New Diamond Technology (NDT) colorless and blue HPHT-grown diamonds. Gem-quality synthetic diamonds from NDT can therefore be distinguished from natural diamonds of similar quality.
One of the authors (BD) has had the opportunity to study HPHT-grown and CVD-grown samples from all producers of gem-quality synthetic diamonds in the last 15 years and this is first time that HPHT-grown diamonds are exhibiting an orange luminescence (usually a characteristic of CVD-grown colorless diamonds) under SWUV light. The most surprising phenomena is, that even visible pinpoint light triggers this orange reaction. This specific type of fluorescence/ phosphorescence offers the possibility for a straightforward and simple “screening test” for most larger diamonds created by NDT (Russia).
We would like to thank all participants and sponsors (OGI Systems, Certiline and HRA Group) of the Mediterranean Gemmological & Jewellery Conference (MGJC) 2015 in Athens organized by IGL Hellas (George Spyromilios) and CGL-GRS Swiss Canadian Gemlab, Canada as well as GRS Gemresearch Swisslab AG for their contributions. This forum allowed us to exchange knowledge and ideas with some of the major stakeholders in the field of diamond research, e.g. DeBeers and GGTL Laboratories (Dr. Thomas Hainschwang) and others (see Rapaport article covering the 2015 MGJ Conference).
We also appreciate that the producers of synthetic diamonds New Diamond Technologies (Russia), Taidiam (Taiwan) and Volldstaedt (Germany) participated in a round table discussion on synthetic diamonds and shared the information on technology of growing diamonds and identification techniques with other labs and conference delegates. A special thanks goes to Nikolai Khikhinashvili (NDT) who brought the largest 10.02ct lab-grow diamond to MGJ Conference 2015 and organized the visit to the facility in Russia, as well as to Dr. Alexander Kolyadin (NDT) for useful technical information and providing samples for this study. We appreciate the help of Bill Vermeulen, CGL-GRS Canada for editing the article. Many thanks to John Chapman for his assistance and contribution in photography. This report would not have been possible with out the scientific input from Dr. Andrey Katrusha, project research advisor for New Diamond Technology (NDT).
Branko Deljanin1, Matthias Alessandri2 , Dr. Adolf Peretti3 , Mikko Åström4, Dr. Andrey Katrusha 5
1CGL-GRS Swiss Canadian Gemlab, Vancouver, Canada
2GRS Lab (Hong Kong) Limited, Hong Kong, China
3GRS Gemresearch Swisslab AG, Lucerne, Switzerland
4M&A Gemological Instruments, Järvenpää, Finnland
5Consultant, St. Petersburg, Russia
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