Modelling defects in diamond to preserve consumer trust in the global diamond trade
Submitting InstitutionUniversity of Exeter
Unit of AssessmentPhysics
Summary Impact TypeTechnological
Research Subject Area(s)
Chemical Sciences: Inorganic Chemistry, Other Chemical Sciences
Earth Sciences: Geology
Summary of the impact
An atomistic modelling program developed at Exeter University has been
used to make a significant, recognised contribution to the strong business
performance of the De Beers Group, the world's leading diamond company. It
gave De Beers the confidence to fund the successful development of new
methods to identify synthetic and treated diamonds, which the company says
has minimised the impact of fraudulent behaviour on consumer confidence,
supported jobs in the global diamond trade, contributed to sales of $7.4bn
in one year alone and was a factor in its decision to invest £20m in new
research facilities in the UK.
Natural diamonds are among the world's most precious natural resources;
diamond jewellery had a global retail value of $72 billion in 2012
according to management consulting firm Bain & Company [5.1]. However,
the last two decades have seen a rapid development in the production of
synthetic diamond and the artificial enhancement of colour of natural
diamond. The increasing quality of counterfeit natural diamonds represents
a serious threat to consumer confidence. Bain & Company reported that
2011 marked the appearance of a large batch of synthetic diamonds believed
by their dealer to be natural, highlighting the need for better techniques
to guarantee the authenticity of natural diamonds and preserve trust in
Research by Robert Jones, Emeritus Professor (at Exeter since 1971) in
Physics has developed new methods to understand colour caused by defects
in diamonds and to distinguish between natural and artificial or
heat-treated diamonds. The new methods are based on prior studies by Jones
into the defects that exist in a wide range of materials. A computer code
— AIMPRO (Abinitio Modelling Program) — that calculates, among other
things, the optical properties of materials was first developed by Jones
[3.1] and now has an international community of users. It analyses the
structural, electrical, optical and mechanical properties of solids in
order to identify material defects. It is unusual in that it uses Gaussian
functions (similar to a normal distribution bell curve) to represent the
quantum-mechanical wavefunctions, and hence the electron density within a
solid, rather than the more commonly used plane waves. Fewer Gaussian
functions than plane waves are needed per atom meaning that larger unit
cells can be investigated.
Jones used AIMPRO to model complex defects in Gallium Nitride and Silicon
[3.2, 3.3]. The code works by arranging atoms in a structure. If the atoms
are aligned incorrectly, the code calculates the force between the atoms
and rearranges the structure until equilibrium is reached. Then the
optical properties and other properties such as the electron energy loss
spectra (EELS) are calculated.
At the request of the Diamond Trading Company (DTC), the rough diamond
distribution arm of De Beers, Jones used AIMPRO to determine the optical
properties and EELS signature of various defects in the diamond. Three
types of defect exist in natural diamond: vacancies and interstitials
(where an atom is either missing from or added to an otherwise regular
structure), impurities (which replace carbon atoms in the lattice), and
dislocations (where neighbouring planes of atoms have slipped in relation
to each other). Jones began by calculating the energy spectrum of the most
stable dislocation that is found in all types of diamond. He showed that
the dislocation itself is not responsible for the colour of brown diamonds
— the most common colour variety of natural diamonds. Instead he proved
that it is the vacancy clusters that can give rise to the brown colour and
he argued that such clusters are introduced by movement of dislocations
when a diamond is plastically deformed under heat and pressure [3.4]. The
vacancy clusters and therefore the brown colour can be removed by exposure
to 2000°C heat. Crucially, Jones discovered that this causes the vacancy
clusters to decay into other types of defect, such as nitrogen-vacancy
defects, the optical properties of which are well known. Counterfeiters
are not yet able to remove these new defects, which show up through
optical spectroscopy used by companies like De Beers to validate their
Further studies considered the optical properties of a number of other
defects such as silicon and nitrogen vacancies, all of which are present
in treated diamond and cause colour changes. More recent work has dealt
with the properties of graphene and related doping mechanisms [3.5],
References to the research
References in bold best indicate the quality of the underpinning
3.1. "LDA calculations using a basis of Gaussian orbitals", P. R.
Briddon and R. Jones, Phys. Stat. Solidi B 217, 131-171 (2000), cited
231 times in WoS.
3.2. "Theory of threading edge and screw dislocations in GaN", J.
Elsner, R. Jones, P. K. Sitch et al. , Phys. Rev.
Lett. 79, 3672-3675 (1997), cited 242 times in
3.3. "Oxygen and dioxygen centers in Si and Ge: Density-functional
calculations", J. Coutinho, R. Jones, P. R. Briddon et al.
, Phys. Rev. B 62, 10824-10840 (2000), cited 180 times
3.4. "Dislocations, vacancies and the brown colour of CVD and natural
diamond", R. Jones, Diamond and Related Materials 18, 820-826
(2009), cited 14 times in WoS. This issue of the journal
contains the proceedings of the 19th European Conference on Diamond,
Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide,
held in Sitges, Spain 7-11th Sept 2008.
3.5. "Plasmon spectroscopy of free-standing graphene films", T. Eberlein,
U. Bangert, R. R. Nair, R. Jones, M. Gass, A. L. Bleloch, K. S, Novoselov,
A. Geim, and P. R. Briddon, Phys. Rev. B 77, 233406 (2008) cited
125 times in WoS.
3.6. "p-type doping of graphene with F4-TCNQ", H. Pinto, R. Jones, J. P.
Goss et al., J. Phys.: Condens. Matter 21, 364220 (2009), cited 33
times in WoS.
Details of the impact
Diamond modelling research at Exeter has made an impact in two principal
areas. It has provided De Beers with the scientific understanding it
needed to develop techniques to identify synthetic and treated diamonds,
maintaining consumer confidence in De Beers' diamond trading and, by way
of the company's long-established dominance, in the diamond industry as a
whole. Secondly, it was a factor in a decision by De Beers to invest £20m
in strengthening its research base in the UK, creating high-level
employment for UK scientists [5.2].
The continued success of De Beers is crucial to the employment of
thousands of people around the world. The De Beers Group employs
approximately 20,000 people, of whom 17,000 are based in Africa. The
company has mining operations in South Africa, Botswana, Namibia and
Canada and is part of the Anglo-American Group that has 145,000 employees
in 30 countries. De Beers sells approximately 40% of the world's rough
diamonds, thus supporting a huge number of downstream jobs in the diamond
trade, from polishing through grading to jewellery manufacture and
retailing. In 2011, De Beers had sales of $7.4 billion with earnings
before interest, taxes, depreciation and amortisation (EBITDA) of $1.7
billion. According to the Head of Physics [5.2] at the De Beers Research
Centre in Maidenhead, a key factor in achieving such a strong performance
was the high consumer demand that drove price increases for rough and
polished diamonds. This, he says, "was underpinned by work supporting
consumer confidence in diamonds in the face of rapid development over the
last 20 years of processes for production of synthetic diamond and
artificial treatment of natural diamond. It is vitally important for the
diamond trade that consumers can buy diamonds without fear of product
Referring specifically to Exeter's contribution, De Beers Head of Physics
said: "Prof Jones's work since 1993 in modelling defects in diamond has
played a major role in helping us build the foundation of knowledge on
which our identification methodology is based and has been an important
factor in enabling the detection and containment of recent attempts to
sell synthetic or treated diamond fraudulently as natural untreated
Jones's research, supported by two collaborative awards in science and
engineering (CASE) PhD studentships funded jointly by EPSRC and De Beers
[5.3, 5.4], helped the company to develop and test the idea that vacancy
clusters are responsible for brown colouration in natural diamonds with
low nitrogen content. It enabled De Beers to understand the mechanism by
which the brown colour is removed by relatively short high temperature
heat treatments, and the identity and stability of by-products of this
heat treatment. The work also helped unravel the link between
nitrogen-vacancy-hydrogen defects and their optical signatures. These
defects have not been detected in any natural diamond but tend to be
present in synthetic diamond, changing its colour. Prof Jones' work helped
De Beers understand these phenomena. De Beers Head of Physics concludes:
"[Exeter's research] has therefore been of fundamental importance in the
development of a robust identification methodology that has safeguarded
consumer confidence and therefore many jobs in the diamond industry."
De Beers cannot quantify the impact of Exeter's work in economic terms;
to remain one step ahead of counterfeiters, the company discloses very
little information about the methods they use to characterise diamonds.
But further evidence that Jones's research has informed practice at De
Beers comes in journal articles published by De Beers scientists [5.5,
5.6, 5.7], which reference the work. It is also highlighted by De Beers'
decision, on the basis of Jones's results, to award two further CASE
studentships in 2009 to academics at the University of Manchester, and to
support further experiments at Helsinki University of Technology. The
published paper from Helsinki [5.8] in 2009 cited Jones's work in their
own calculations and acknowledged discussions with Jones during their own
research. Jones's work is generally accepted as explaining the role of
vacancy clusters in the colour of diamonds.
According to De Beers Head of Physics, De Beers has an increasingly
strong research base within the UK, employing 56 highly trained people,
including many PhD scientists, at its DTC research centre in Maidenhead.
The DTC collaborates closely with Element Six (E6), part of the De Beers
Group and the world's leading supplier of synthetic industrial diamonds.
De Beers Head of Physics reports that in 2013 E6's global R&D will be
consolidated into the E6 Global Innovation Centre (http://www.e6.com/gic)
near Oxford, where "a pipeline of innovative products will be developed
for customers in industries from oil and gas drilling to machining and
He said: "This £20m investment is consolidating E6's existing global
innovation teams in the UK and the choice of location was strongly
influenced by the excellence of UK research in diamond science as
exemplified by Professor Jones at Exeter." He added: "De Beers organizes
an annual conference to encourage presentation and discussion of new
research relevant to the diamond industry at which Prof Jones has been an
active and valued contributor." [5.9]
Sources to corroborate the impact
5.1. Figure 1.1 in The Global Diamond Report 2013:
5.2. Letter from Head of Physics at De Beers Research Centre in
Maidenhead, UK. The letter describes the nature and scale of De Beers
business and the contribution made by Prof Jones to its development of
methods to distinguish between naturally colourless, heat treated and CVD
diamond. The depth of detail supplied reflects De Beers need to also
protect their commercial interest. De Beers are obviously reluctant to put
details of anti-counterfeiting measures in the public domain.
5.3. "Modelling of Point and Extended Defects in Group IV
Semiconductors", PhD thesis, Naomi Fujita, University of Exeter (2009).
CASE award funded by De Beers, supervised by Prof R. Jones.
5.4. "Defects and dopants in carbon related materials", PhD thesis, Hugo
Pinto, University of Exeter (2009). CASE award funded by De Beers,
supervised by Prof R. Jones.
5.5. "Brown diamonds and high pressure high temperature treatment", D.
Fisher, Lithos 112S 619-624 (2009). This journal article by a De
Beers scientist describes methods for determining the history and origin
of diamonds, making reference to the work of Prof Jones, and acknowledging
5.6. "Charge transfer effects, thermo — and photochromism in single
crystal CVD synthetic diamond", R. U. A. Khan, P. M. Martineau, B. L.
Cann, M. E. Newton and D. J. Twitchen, J. Phys.: Condens. Matter 21,
364214 (2009). This journal article by De Beers scientists describes the
optical signature by which CVD synthetic diamond can be identified, and
makes due reference to the work of Prof Jones.
5.7. "Brown colour in natural diamond and interaction between the brown
related and other colour-inducing defects", D Fisher, S J Sibley and C J
Kelly, J. Phys.: Condens. Matter 21, 364213 (2009). This journal
article by De Beers scientists describes optical absorption spectra of
different types of diamond, and makes due reference to the work of Prof
5.8. "Properties of optically active vacancy clusters in type IIa
diamond", J.-M. Mäki, F. Tuomisto, C. J. Kelly, D. Fisher and P. M.
Martineau, J. Phys.: Condens. Matter 21, 364216 (2009). The
article makes reference to the work of Prof Jones and acknowledges his
5.9. Prof Jones received invitations to speak at conferences organised by
scientists employed by De Beers, including the 19th European Conference on
Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon
Carbide, held in Sitges, Spain 7-11th Sept 2008.