A Defect Study and Classification of Brown Diamonds with Deformation-Related Color

For this study, the properties of a large sample of various types of brown diamonds with a deformation-related (referred to as “DR” in this work) color were studied to properly characterize and classify such diamonds, and to compare them to pink to purple to red diamonds. The acquisition of low temperature NIR spectra for a large range of brown diamonds and photoexcitation studies combined with various treatment experiments have opened new windows into certain defect characteristics of brown diamonds, such as the amber centers and naturally occurring H1b and H1c centers. It was determined that the amber centers (referred to as “AC” in this work) exhibit rather variable behaviors to annealing and photoexcitation; the annealing temperature of these defects were determined to range from 1150 to >1850 °C and it was found that the 4063 cm−1 AC was the precursor defect of many other ACs. It is suggested that the amber centers in diamonds that contain at least some C centers are essentially identical to the ones seen in diamonds without C centers, but that they likely have a negative charge. The study of the naturally occurring H1b and H1c link them to the amber centers, specifically to the one at 4063 cm−1. Annealing experiments have shown that the H1b and H1c defects and the 4063 cm−1 AC were in line with each other. The obvious links between these defects points towards our suggestion that the H1b and H1c defects are standalone defects that consist of multiple vacancies and nitrogen and that they are—in the case of brown diamonds—a side product of the AC formation. A new classification of DR brown diamonds was elaborated that separates the diamonds in six different classes, depending on type and AC. This classification had been completed recently with the classification of brown diamonds with a non-deformation-related color (referred to as “NDR”), giving a total of 11 classes of brown diamonds

Spectral Differentiation of Natural-Color Saltwater Cultured Pearls from Pinctada Margaritifera and Pteria Sterna

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UV-VIS-NIR Reflectance Spectroscopy of Natural-Color Saltwater Cultured Pearls from Pinctada Margaritifera

International audienceNatural-color saltwater cultured pearls from Pinctada margaritifera were studied by diffuse reflectance UV-Vis-NIR spectroscopy to identify the absorption features associated with their various colors. Nine patterns observed in the visible range demonstrated that individual colors are caused not by one pigment but by a mixture of pigments

The origin of color in natural C center bearing diamonds

International audience"The properties of 152 natural diamonds with C centers - detectable by the absorptions at about 1344 and/or 2688 cm− 1 in the infrared spectra - were analyzed in order to better understand their origin of color. While such diamonds are generally thought to be yellow, type Ib natural diamonds are usually not so, but mainly orange-yellow, orange, brown, 'olive' (a mixture of yellow with brown and/or gray with always a greenish component) and mixtures thereof. The only natural diamonds found to be of pure yellow coloration were - with very few exceptions - type IaA diamonds with a very minor Ib component, of cuboid-octahedral growth, often so-called re-entrant cubes. This was verified by the analysis of over 70,000 bright yellow and over 20,000 yellow-orange melee diamonds (i.e. diamonds weighing less than 0.20 cts) submitted for testing at the laboratory. In natural type Ib diamonds of octahedral growth the color is strongly influenced by vacancy-related defects that originate mainly from plastic deformation; natural type Ib diamonds of regular octahedral growth generally show distinct deformation-related strain and often some associated color zoning or 'colored graining' along octahedral planes. None of the nickel-rich, C-center-containing natural diamonds included in this study showed any specific Ni-related absorption band in the visible range spectrum that had an influence on color. The "olive" to brown color in type Ib diamonds was found to be caused by a combination of continuum absorption with increased absorbance from the NIR to about 480 nm plus distinct NV− center absorption.

NATURAL DIAMONDS MISTAKENLY IDENTIFIED AS NPD SYNTHETIC DIAMONDS

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Residual radioactivity of treated green diamonds

International audienceTreated green diamonds can show residual radioactivity, generally due to immersion in radium salts. We report various activity measurements on two radioactive diamonds. The activity was characterized by alpha and gamma ray spectrometry, and the radon emanation was measured by alpha counting of a frozen source. Even when no residual radium contamination can be identified, measurable alpha and high-energy beta emissions could be detected. The potential health impact of radioactive diamonds and their status with regard to the regulatory policy for radioactive products are discussed