Diamond Dictionary by GHI

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(Select a letter from above to go to that “page” of the dictionary below.)

A-band: Excited by CL, may vary its position in different diamonds from 430 to 490 nm. Its position in low nitrogen diamonds and IIa diamonds is 440 nm, and it is its most common position.

Absorbance: Relative intensity of transmitted light. Absorbance is defined as: A = log10(Itransmitted/Iinitial).

Absorption: Process of absorption of light by electrons in a material. The absorbed light energy is usually converted into invisible heat energy. The absorbed light is therefore not transmitted all the way through the material.

Annealing: Heating, usually follows irradiation to change the color of diamonds. For instance, some blue, green and yellow diamonds can be converted by annealing into intense yellow, orange and pink.

Atm (atmosphere): Unit for pressure.1 atm = 1 kg/cm2

BARS press:
Acronym for the Russian “Bespressoovye Apparaty tipa Razreznaya Sfera” or in English “Split Sphere No Press Apparatus”. In this apparatus the high pressure is obtained by injecting liquid into a compression barrel. Inside sits a reaction cell containing the heating element, seed crystal and carbon source material and the metal solvent. BARS are developed in Russia to grow single crystal diamonds for industrial (Russian producers) and jewelry purposes (used by AOTC and Gemesis).

Belt Type press: Designed by Tracy Hall from GE to make the first polycrystalline diamond and used today in modified versions by other industrial producers to grow diamonds. Carbon (diamond powder) is placed in a capsule, which is placed in a die and swung into position between two anvils and subjected to extreme pressure and heat.

Boron: The element responsible (as an impurity replacing carbon) for the semi-conducting properties and the gray to blue color in type IIb diamonds.

Carat: Unit for weight equal to 0.20 grams.

CIS (Cross-referencing Identification System): Developed by EGL USA Group to store all data (e.g. identification number, weight, measurements, shape, results from DiamondSureã, color, clarity, fluorescence, photos, UV-VIS-NIR, FTIR, PL and CL spectra along with other necessary advanced tests) in one CIS computer system. The system will be interactive to enable the searching and cross-referencing of data and will permit statistical analysis of each of the groups, e.g. percentage of each characteristic present in all diamonds tested by laboratories. It is used to better communicate research and identification data between EGL USA Group and GHI labs in North America and India.

CL (cathodoluminescence): A luminescence excited with electrons. CL can be applied only for defects, which are effective recombination centers (like the H3 or N3 nitrogen related centers) for free electrons. In contrast, ineffective recombination centers (like the 638nm nitrogen related center) cannot be excited in CL. A technical advantage of CL is the easy and inexpensive excitation of wide band gap semiconductors, like diamond.

cm-l: Wavenumber, a unit used for measurements of energy of photons in infrared spectral range (400 – 6000cm-1).

Covalent bonding: A covalent bond is an electronic link between atoms resulting from the sharing of electrons between atoms. Diamond has covalent bonding.

CPF (Cross Polarized Filters): Two polarizing filters are “crossed” when arranged one in front of the other and rotated until minimum of light is transmitted to the eye. The polarization-optical method has been developed for the evaluation of internal mechanical stress in diamonds (Orlov 1973; Varshavskii 1968; Lang 1967a).

Crystal: Material with regular (repeatable) arrangement of atoms forming atomic planes.

CVD (Chemical Vapor Deposition): Method of growing polycrystalline and single-crystal diamonds from carbon-containing gas without pressure.

CZ (Cubic Zirconia): A form of zirconium oxide doped with stabilizing additive. Used as a major diamond imitation and as an artificial gemstone in inexpensive jewelry.

DiamondSure©: A De Beers developed spectroscopic instrument used for screening loose diamond imitations and lab-grown diamonds based on absence of N3 center (at 415nm).

DiamondView©: A De Beers developed instrument used for identification of loose laboratory grown diamonds based on study of growth structure under strong short wavelength UV light.

EDXRF (Energy Dispersive X-ray Fluorescence): An X-ray spectroscopic method used to identify chemical elements in major or trace quantities from sodium (atomic number 11) onwards. It is a diagnostic test for low quality lab-grown diamonds by detecting metals (nickel, iron and cobalt).

Fluorescence: A short lifetime luminescence (fast luminescence). Visually fluorescence stops immediately after the excitation is switched off. Typically lifetime of fluorescence in diamonds is about one microsecond (one millionth of a second). Fluorescence is the most important kind of luminescence used by gemologists.

FTIR (Fourier-Transform Infrared spectroscopy): An optical absorption technique for analyzing impurities in diamonds (nitrogen, hydrogen, boron) and carbon bonding environments. FTIR is usually used in infrared spectral range from 400 – 6000cm-1. This method is used for identification of treatments of natural diamonds, laboratory-grown diamonds and other gems.


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H (hydrogen): Impurity sometimes present in type Ia natural diamonds (often causing cloudy appearance) and CVD-grown diamonds. Optical centers formed by hydrogen in diamonds of different type and origin may be different, exhibiting different lines in infrared spectra.

H3 center: A nitrogen-related defect exhibiting in optical spectra ZPL at 503nm. The H3 center is common in absorption and luminescence spectra of nitrogen-containing natural and synthetic diamonds after any irradiation and subsequent annealing at temperatures above 500°C. The H3 centers are formed of A aggregates of nitrogen and vacancies.

High resolution spectroscopy: It means resolution of spectra. In gemology it is a resolution of 0.5nm and less. For physicists studying diamond spectroscopy at low temperatures it should be 0.1nm and less.

HPHT (High Pressure High Temperature): Process of growing diamonds at a pressure of 60 kBar and a temperature of 1300 degrees in specially designed presses. Using the same presses but applying higher pressures and temperatures natural diamonds can be treated to change their color to green-yellow and yellow (type Ia diamonds), colorless and pink (type IIa diamonds) and blue (type IIb diamonds).

Inclusion: Internal visible features within cut or uncut gem materials. Inclusions could be crystals, twinning wisps, needles (natural diamonds) or flux, metals (lab-grown diamonds). Fractures and cavities could be present in both materials.

Irradiation: Bombardment by atomic particles, or the emanations of radioactive substances. It may be natural or artificial. It may change the color of diamond to blue and green.


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Luminescence: General term used to describe the emission of light by a substance under illumination with short wavelength light (usually UV light), electrons or X-rays.

LW UV light: Long Wavelength Ultra Violet light. In gemology the term LW UV is commonly used for ultraviolet radiation at a wavelength of 365nm.


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N3 center: An optical center with ZPL at 415nm. The N3 center is a common feature in most type Ia natural diamonds containing the B aggregates. It is rarely observed in synthetic diamonds. Most of type Ia diamonds have yellowish to yellow tint color due to absorption of light by the N3 center in the blue range of visible spectrum (“cape diamonds”).

Nitrogen: An element which is dispersed within the crystal lattice of diamond replacing carbon atoms. Nitrogen produces absorption bands in the blue part of visible spectra (the cause of yellow color) and 1100 – 1300 cm-1 range in infrared spectra.

nm (nanometer): A common unit of wavelength of light in visible and UV spectral range. One nanometer is one billionth of a meter (1 nm = 10-9 m).

Octahedron: An eight-sided crystal, each face being an equilateral triangle. It is one of the seven basic forms belonging to the highest class of symmetry in the cubic crystal system.

Phosphorescence: A long lifetime luminescence, which is observed as a luminous afterglow persisting after the excitation source has been shutoff. In diamonds the lifetime of phosphorescence can be as long as a few minutes.

Physical properties: Observable and measurable characteristics of materials related to their internal atomic structure and interatomic forces, e.g. optical transparency, density, hardness, thermal conductivity, color.

PL (Photoluminescence): A luminescence excited with light. The main process of PL excitation is the resonance interaction of electrons of optical centers with an electromagnetic wave.

ppm (parts per million): A unit used for measuring concentration of impurity atoms (e.g. nitrogen and boron) in natural and lab-grown diamonds


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Raman spectroscopy: An optical method examining vibrational interactions between atoms, where the incident photon contributes, or receives only a small amount of energy to excite or absorb atomic vibrations. Since Raman spectra are unique for any crystal, the Raman spectroscopy is the most reliable method to distinguish between diamond and imitation.

Raman spectrometers: These use high resolution microscopes to focus laser beam (excited spot can be as small as 0.5 micron) and is used to study color centers in diamonds.

SW UV light: Short Wavelength Ultra Violet light. In gemology the term SW UV is commonly used for ultraviolet radiation at a wavelength of 254nm.

Synthetic diamond: Laboratory grown diamond, which have the same composition, structure and physical properties as naturally occurring diamond. However, defect structure of synthetic diamond differs from that of natural diamond.

Synthetic Moissanite: Silicon carbide manufactured at high temperature (2300°C) by vapor transfer in vacuum or in argon gas.

Treatment (enhancement): A process designed to artificially change the appearance (color and clarity) and properties of diamonds and other gems.

Type I diamond: A category of diamonds, which contain nitrogen as a major impurity.

Type Ia diamond: Type I diamonds with nitrogen present in aggregated forms, up to 3000 ppm of nitrogen. Type la is the most common type of natural diamond (97%). Type Ia diamonds can be of different color but blue: near-colorless, “Cape” yellow, orange or brown.

Type Ib diamond: Type I diamond with dispersed nitrogen atom replacing individual carbon atoms in diamond lattice, up to 500 ppm nitrogen. Type Ib diamonds are rare in nature, but most synthetic diamonds are type Ib, “Canary” yellow and brownish yellow.

Type II diamond: A category of diamonds, which do not contain detectable amount of nitrogen.

Type IIa diamond: Very rare in nature (less than 2%). The most pure diamonds with no detectable content of any impurity. Type IIa natural diamonds may be colorless, or have brown and pink color.

Type IIb diamond: Extremely rare in nature (around 0.1%) diamonds containing boron as a major impurity. Type IIb diamonds are semiconductors. Type IIb diamonds are blue or gray-blue in color.

UV-VIS-NIR spectroscopy: An optical absorption method for detection of optical centers in Ultraviolet Visible-Nearinfrared spectral range. It is the primary method for determining color origin in diamonds and other gemstones.

UV lamp: A lamp producing ultraviolet radiation. UV lamp is used to excite and examine fluorescence in gems, what may be an aid in identification or detection of treatments.


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ZPL:Zero-phonon line. Primary line in spectrum bf an optical center. ZPL represents pure electronic transition at a center and is its characteristic feature.

Reference courtesy of GHI (Gemology Headquarters International); Branko Deljanin & Dusan Simic

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