This article addresses the possible defects of a diamond crystal. For a broader discussion of diamonds, see diamond. For other uses of the word diamond, see diamond (disambiguation). A scattering of round-brilliant cut diamonds shows off the many reflecting facets. ... Diamond is: the name of a form of carbon valued for its beauty in jewelry and its hardness in industrial uses; a square or rhombus whose longest diagonal is usually aligned vertically; a playing card marked with a stylized red diamond (♦), or when plural, the corresponding card suit; or the...

Crystallographic defects in the crystal lattice of diamond are common; they may be the result of extrinsic substitutional impurities, or intrinsic (interstitial and structural) anomalies. All diamonds possess crystal lattice defects of some sort; the defects themselves may be either anthropogenic or natural, epigenetic or syngenetic. The material properties of diamond are affected by these defects and determine to which type a diamond is assigned; the most dramatic effects are on a diamond's color and semiconductivity, as explained by the band theory. Crystalline solids have a very regular atomic structure: that is, the local positions of atoms with respect to each other are repeated at the atomic scale. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... A scattering of round-brilliant cut diamonds shows off the many reflecting facets. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... This article addresses the material properties of diamond. ... A semiconductor is a material with an electrical conductance that is intermediate to those of an insulator and a conductor. ...

The defects can be detected by different types of spectroscopy, including ESR, photoluminescence in ultraviolet light, and absorbtion of infrared light. The resulting absorption spectrum can then be analyzed, identified, and used to separate natural from synthetic or enhanced diamonds. Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ... // Overview Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) is a spectroscopic technique which detects species that have unpaired electrons, generally meaning that it must be a free radical, if it is an organic molecule, or that it has transition metal ions if it is an inorganic complex. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ... IR spectrum of a thin film of liquid ethanol. ... An absorption spectrum is a diagram depicting the wavelengths of electromagnetic radiation absorbed by a material, usually a gas or a solute. ... Synthetic diamond is diamond produced through chemical or physical processes in a laboratory. ... This article addresses treatments designed to enhance the gemological characteristics of diamond. ...

Extrinsic defects

Infrared spectrum of Type IaB diamond. (1) region of nitrogen impurities absorption, (2) B2 peak, (3) self absorption of diamond lattice, (4) hydrogen peaks

The burning of diamonds in a vacuum and the analysis of resultant gases and remnant matter has shown that diamonds can contain many elements present as substitutional (i.e., replacing carbon atoms in the lattice) impurities: nitrogen, boron, hydrogen, oxygen, sulfur, nickel, cobalt, and iron have all been thus detected. Image File history File links Innfra Red specto of diamond. ... Image File history File links Innfra Red specto of diamond. ... This article is about absence of matter. ... Gas (actually, as), the GNU assembler, is the default GCC back-end. ... A chemical element, often called simply element, is a substance that cannot be divided or changed into different substances by ordinary chemical methods. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black Atomic mass 10. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10 , 4, d Density, Hardness 8908 kg/m³, 4. ... General Name, Symbol, Number cobalt, Co, 27 Chemical series transition metals Group, Period, Block 9 , 4, d Density, Hardness 8. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4, d Density, Hardness 7874 kg/m3, 4. ...

Nitrogen

The most common impurity in diamond is nitrogen, which can comprise up to 1 percent of a diamond by mass. Nitrogen as a diamond impurity was first identified in 1959 by Kaiser and Bond of Bell Telephone (Kaiser and Bond 1959). Previously, all lattice defects in diamond were thought to be the result of structural anomalies; later research revealed nitrogen to be present in most diamonds and in many different configurations. 1959 was a common year starting on Thursday of the Gregorian calendar. ... AT&T Corporate Logo, 1969-1983 The Bell System is an informal name given to the US telecommunications company American Telephone & Telegraph Company (AT&T) before AT&T divested its local exchange telephone service operating companies on January 1, 1984. ...

The light absorption and other material properties of diamond are highly dependent upon nitrogen content and aggregation state. Although all aggregate configurations cause absorption in the infrared and ultraviolet, diamonds with high levels of nitrogen are usually colorless. It is the interactions between different aggregate configurations which cause color rather than the aggregates themselves (Anderson et. al. 1998, p. 215). Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ...

Main nitrogenous defects

There are more than 50 forms of nitrogenous defects that occur in diamonds, and the three main forms observed in visible and infrared spectra are as follows: Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ...

C center 

C center defects consist of single substitutional nitrogen atoms in the diamond lattice that are spacially isolated. These are easily seen in ESR spectra (in which they are called P1 centers). C form defects impart a deep yellow to brown color; these diamonds are classed Type Ib and are commonly known as canary diamonds, which are rare in gem form. In most cases synthetic diamonds contain a high level of nitrogen in the C form because nitrogen from the atmosphere is difficult to exclude from the synthesis process; as little as one nitrogen atom per 100,000 carbon atoms will produce a deep yellow (Nassau 1980, p. 191). Because the nitrogen atoms have five available electrons (one more than the carbon atoms they replace), they act as deep donors; that is, each substituting nitrogen has an extra electron to donate, thereby forming a donator energy level within the band gap. Light with energy above ca. 2.5 eV and above can excite the donor electrons into the conduction band, thereby allowing light absorption (Nassau, p. 332).

A center 

The A center is probably the most common defect in natural diamonds. The structure of this form remains a topic of debate: first researchers supposed that it consisted of nitrogen, but later the conclusion was reached that the A center was due to microscopic platelets (now platelets connected with B2 peaks). This theory remained for twenty years, until N. V. Sobolev offered the theory of two nitrogen atoms (bonded strongly together as a molecular pair) replacing carbon in the diamond lattice. Recent research has shown the accuracy of this model. The A center does not cause discoloration on its own; these diamonds are classed as Type IaA.

B1 center 

The structure of B1 defects is not yet clear. The most popular explanation involves four nitrogen atoms surrounding a vacancy. These diamonds are classed as Type IaB; most gem diamonds contain a mixture of A center and B center defects, together with N3 centers, the combination producing the yellow-brown Cape series. As with A center defects, B1 center defects do not cause discoloration by themselves (Anderson et. al., p. 215).

Properties For alternative meanings see atom (disambiguation). ... A gemstone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewellery. ... Properties The electron is a subatomic particle. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... In physics and quantum chemistry, an energy level is a quantized energy of a bound quantum mechanical state. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... In semiconductors and insulators, the conduction band is the range of electron energy, higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current. ...

Minor nitrogenous defects

N3 center 

The N3 center consists of three nitrogen atoms surrounding a vacancy in a flat configuration. It can occur along with other aggregate forms, with which it produces strong colors—particularly with A and B1 centers (Anderson et. al., p. 215). The N3 center is paramagnetic so its structure is well-developed by the ESR method. In ultraviolet fluorescence spectra, this defect produces a characteristic absorption line in the far violet at 415.5 nm, termed the N3 line (O'Donoghue 2002, p. 52).

Paramagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin as well as electron orbital angular momentum, to align with an external magnetic field. ...

Boron

Diamonds containing boron as a substitutional impurity are termed Type IIb. Only one percent of diamonds are of this type, and most are blue to grey (O'Donoghue 2002, p. 52). The boron acts as an acceptor; that is, because the substituting boron atoms have one less available electron than the carbon atoms they replace, each boron atom creates an electron hole in the band gap that can accept an electron from the valence band. This allows red light absorption, and due to the small energy (c. 0.4 eV) needed for the electron to leave the valence band, holes are created in the latter even via thermal heat at room temperatures. These holes can move in an electric field and render the diamond electrically conductive (i.e., a p-type semiconductor). Very little substitutional boron is required for this to happen—a typical ratio is one boron atom per 1,000,000 carbon atoms (Nassau, p. 333). In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ... In solids, the valence band is the highest range of electron energies where electrons are normally present at zero temperature. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... Electrical conductivity is a measure of how well a material accommodates the transport of electric charge. ... A P-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case positive) charges. ...

Type IIb diamonds transmit in the ultraviolet down to c. 250 nm but do not absorb in the visible region apart from the far red (hence the blue color); they may phosphoresce blue after exposure to shortwave ultraviolet. Synthetic diamonds containing boron are blue and either Type IIb or a mixture of IIb and IIa material (O'Donoghue 2002, p. 52, 46). Phosphorescence is the result of a radiative (light emitting) transition involving a change in the spin multiplicity of (in most cases) a molecule from excited state singlet to excited state triplet. ...

Intrinsic defects

Every natural diamond crystal contains typical intrinsic or self-defects: vacancies, dislocations, and interstitial atoms. For the syntaxic operation, see Dislocation (syntax) For the medical term, see Dislocation (medicine) In materials science a dislocation is a linear crystallographic defect, or irregularity, in crystal structure. ...

Vacancies

A vacancy is an empty position in a diamond's lattice. Vacancies may be affected or created by radiation damage—high-energy subatomic particles knock carbon atoms out of the lattice. This may be the result of natural or artificial radiation (see Diamond enhancement - Irradiation). Vacancies are detectable via ultraviolet luminescence. Radiation generally means the transmission of waves, objects or information from a source into a surrounding medium or destination. ... Helium atom (schematic) Showing two protons (red), two neutrons (green) and two electrons (yellow). ... This article addresses treatments designed to enhance the gemological characteristics of diamond. ... Luminescence is any emission of electromagnetic radiation. ...

Carbon atoms neighboring a vacancy may jump into a vacant place and leave an empty position in the diamond lattice; by this process a vacancy can migrate through the diamond, and can form compound defects with other vacancies or nitrogenous defects.The empty positions are termed F-Centers and are occupied by single electrons, which are able to be excited to higher energy levels, thus absorbing visible light and producing color (Nassau, pp. 323–324). The F-Centers usually create a green color that can be modified by subsequent annealing. An F-Center, from the German Farbenzentrum, is the anionic vacancy in a crystal filled by one or more electrons (depending on the charge of the missing ion in the crystal). ... The word anneal has several meanings: In metallurgy and materials science annealing is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ...

Dislocations

The purest diamonds, which contain little if any extrinsic impurities (Type IIa), may have their color modified by structural dislocations or plastic deformations, which are breaks in the translational symmetry of the lattice. There are two important types of dislocations in diamond: the glide set, in which bonds break between layers of atoms with different indices (those not lying directly above each other); and the shuffle set, in which the breaks occur between atoms of the same index. The dislocations produce dangling bonds which introduce energy levels into the band gap, enabling the absorption of light (Kolodzie and Bleloch). A chemical bond is the phenomenon of atoms being held together in molecules or crystals. ...

These defects are thus believed to cause brown, pink, or purple coloration. Like boron-containing Type IIb diamonds, Type IIa diamonds transmit in the ultraviolet down to 250 nm. If treated with high temperatures and high pressures, the dislocations can be "healed" and the color removed (see next section).

B2 center 

Some diamonds contain platelets in the 100 plane visible by microscope. This intriguing defect causes a sharp peak at 1600 cm^-1 in IR spectra.

Effects of HTHP on defects

Experiments with synthetic and natural diamonds treated at high temperatures and high pressures (HTHP) have shown that, with time, lattice defects can be altered or repaired. In Type IIa diamonds with structural dislocations, single nitrogen vacancies are created—as indicated by absorption peaks at 3760 cm^-1—and much of the original color is removed (O'Donoghue and Joyner 2003, p. 35). HTHP can also be used to remove color from diamonds with B1 centers. No single nitrogen is introduced in this case; however, N3 centers sometimes are, and impart a light yellow-grey color (Deljanin and Fritsch, 2000).

Diamonds with C form aggregates can be converted to the A form. This process is called aggregation of nitrogen because nitrogen atoms tend to assemble to the aggregate locations with lower energy. The next step of this process is conversion of A form to B1 form of nitrogen with attendant constitution of platelets (B2 center). Possibly when most of the nitrogen is in B1 form the platelets disintegrate with the formation of micro-voids. Conversion of A form into B1 form takes place at noticeably higher temperatures and/or longer treatment times.

References

• Anderson, B., Payne, J., Mitchell, R. K. (ed.) (1998). The spectroscope and gemmology, pp. 214–222. Robert Hale Limited; Clerkwood House, London. ISBN 071980261X
• Deljanin B., Fritsch E. (2001). Les diamants de Type I traités à HPHT: Novatek, General Electric, Russes et Suedois. Revue de Gemmologie, Association Française de Gemmologie, Jan./Feb. 2001, Vol. 141/142, pp. 54–58.
• Evans T. and Qi Z. The kinetics of aggregation of nitrogen atoms in diamonds. Proc. Roy. Soc. London A381, 1982. p. 238-242.
• Kaiser, W. and Bond, W. L. (1959) Nitrogen, A Major Impurity in Common Type I Diamond Pyis. Rev. 115, 875-863.
• Kiflawi I., Bruley J. The nitrogen aggregation sequence and the formation of voidites in diamond. Diamond and Related Materials 9 (2000) 87–93
• Kolodzie, A. T., Bleloch, A. L. Investigation of band gap energy states at dislocations in natural diamond. Cavendish Laboratory, University of Cambridge; Cambridge, England.
• Nassau, Kurt. (1980). Gems made by man. Gemological Institute of America; Santa Monica, California. ISBN 087330161
• O'Donoghue, M. (2002). Synthetic, imitation & treated gemstones. Elsevier Butterworth-Heinemann, Great Britain. ISBN 0705631732
• O'Donoghue, M., Joyner, . (2003). Identification of gemstones, pp. 28–35. Butterworth-Heinemann, Great Britain. ISBN 0750655127
• Taylor W. R., Canil D. and Milledge H. J. Kinetics of Ib IaA nitrogen aggregation in diamond. Geochemica and Cosmochemica Acta Vol. 60 1996 y. p. 118-124.
• Woods G. S., 1986. Platelets and the infrared absorption of Type Ia diamonds. Proceeding of Royal Society of London 407, 219-238.