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These faceted diamonds are treated by irradiation, HPHT, and multiprocess treatments, respectively, and they range in size from 0.24 to 0.42 ct.
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With the increasing availability of treated-color diamonds on the market, their characterization is becoming more and more critical to the jewelry testers and customers. In this investigation, ten color diamonds treated by irradiation (4 pieces), HPHT (3 pieces), and multiprocess (3 pieces) were examined by spectroscopic methods. These diamonds are...
Citations
... Blue and green diamonds display visible spectra with a large band between 400 and 600 nm, which may be associated with the H3 defect (N-V-N defect) [2]. The GR1 center is attributed to the neutral isolated vacancy (V • ) located at 741 and 744 nm, which is seen in both green and blue diamonds [34]. ...
... Blue and green diamonds display visible spectra with a large band between 400 and ~600 nm, which may be associated with the H3 defect (N-V-N defect) [2]. The GR1 center is attributed to the neutral isolated vacancy (V°) located at 741 and 744 nm, which is seen in both green and blue diamonds [34]. ...
Color induction in nitrogen-contaminated diamonds was carried out via various procedures that involve irradiation, thermal treatments (annealing), and more. These treatments affect vacancy defect production and atom orientation centers in the diamond lattice. Natural diamonds underwent color enhancement treatments in order to produce green, blue, and yellow fancy diamonds. The aim of this study was to follow the changes occurring during the treatment, mainly by EPR spectroscopy, which is the main source for the determination of the effect of paramagnetic centers (carbon-centered radicals) on the color centers produced via the treatments, but also via visual assessment, fluorescence, UV-vis, and FTIR spectroscopy. The results indicate that diamonds containing high levels of nitrogen contamination are associated with high carbon-centered radical concentrations. Four paramagnetic center structures (N1, N4, and P2/W21) were generated by the treatment. It is suggested that the N4 structure correlates with the formation of blue color centers, whereas yellow color centers are attributed to the presence of N1 species. While to produce blue and yellow colors, a thermal treatment is needed after irradiation, for treated green diamonds, no thermal treatment is needed (only irradiation).
... Such thermal treatment involved controlled heating and cooling. [18][19][20] Heating in the 400-1300 1C temperature range in the absence of molecular oxygen (to avoid oxidation of the diamond to carbon dioxide) is conducted until the desired color is achieved. This process eliminates undesirable color centers and improve diamond color quality. ...
The modification of nitrogen-contaminated diamonds into color-enhanced diamonds is usually achieved by irradiation and thermal treatment (annealing). These treatments affect nitrogen contamination chemical bonding, vacancy concentration, and atom orientation centers in the diamond lattice. In this study, natural diamonds were subjected to irradiation and thermal annealing color enhancement treatments to produce green, blue, and yellow fancy diamonds. The study followed the changes that occur during treatment relying on visual assessment, fluorescence, UV-vis, FTIR, and EPR spectroscopy to characterize paramagnetic centers. The results indicated that diamonds containing high levels of nitrogen contamination presented a relatively high carbon-centered radical concentration. Two paramagnetic groups with different g-values were found, namely, low g-value centers of 2.0017-2.0027 and high g-value centers of 2.0028-2.0035. It is suggested that the 2.0017-2.0022 centers correlate with blue centers, whereas the 2.0023-2.0027 centers correlate with yellow centers. It was also found that thermal treatment was required to produce blue and yellow fancy diamonds, whereas no such treatment was needed to produce green diamonds.
... Previously, irradiation and/or annealing studies have been performed on HPHT synthetic type IIb diamonds [12], type IIb CVD synthetic diamond [13], and 12 naturally sourced IIb diamonds [14] along with other diamond materials [15][16][17][18][19][20][21][22]; these also were electron-irradiated and isochronally annealed. In a prior study [14], some limited spatial mapping was performed on an irradiated diamond over a narrow annealing range; this series of experiments seeks to expand on those results. ...
... Nitrogen-vacancy centers can be formed in relatively high concentrations at temperatures > 600°C and its intensity can increase several orders of magnitude over the temperature range examined here [14]. The generation of NV centers with irradiation and low temperature annealing has been documented numerous times [15,[46][47][48][49]; it is the most common method to produce pink-to-red color in treated natural diamonds and post-growth processing of CVD and HPHT laboratory-grown diamonds. ...
Natural blue diamonds are among the rarest and most valuable of gemstones; however, they are occasionally treated by a variety of methods to improve the color or in attempts to obscure the evidence of treatment. In this study, two sections were cut from a rough naturally sourced type IIb diamond. One was subjected to electron irradiation along one edge. Subsequently, both were isochronally annealed from 300oC to 1200oC and the optical defects were documented by changes in infrared (IR) absorption and photoluminescence spectroscopic mapping. The thermal behavior of these centers (TR12, 3H, NV⁰, GR1, 648.2 and 776.4 nm centers among others) along with their spatial distribution in the irradiated and non-irradiated diamond provided additional insights into their configuration.
After irradiation, the uncompensated boron concentration as determined by IR spectroscopy for this sample showed a pronounced decrease particularly at positions close to the irradiation edge. This uncompensated boron decreased further with low temperature annealing (300–600oC) principally due to interstitial migration. At temperatures greater than 600oC, the uncompensated boron concentration rebounded due to vacancy migration that likely depletes or annihilates compensating defects. Among the photoluminescence (PL) defects, the 3H center (ZPL = 503.5 nm) showed a much greater thermal stability in the irradiated sample compared to its non-irradiated counterpart.
... Many lines arise after ion implantation , but these systems have not yet been described in the spectra of natural crystals. Many unassigned lines were observed in spectra of diamonds after irradiation and annealing (Wang et al. 2018). In natural diamonds, radiation centers with a high concentration can also be found (Breeding et al. 2018;Vasilev et al. 2018a, b). ...
... Many sharp unassigned lines were detected in the PL spectra of synthetic diamonds (Eaton-Magana et al. 2017;Loudin 2017). Recent studies of PL in natural diamonds in the NIR range have revealed some previously unreported systems (Hainschwang 2014;Wang et al. 2018;Vasilev 2019). These studies have shown the necessity for revealing the diversity of PL-active systems in natural diamonds in the NIR range. ...
... nm, 918/930 nm, 946.5/961.5 nm, and 981/994 nm (Fig. 2a). The spectrum with this system is shown in (Wang et al. 2018). The energy spacing ΔE between the lines in the doublet is 0.016 eV; the distance between the doublets is 0.043 eV; and the line width (FWHM) of the first doublet in the spectra of various crystals varies from 0.004 to 0.006 eV. ...
Natural diamond remains the source of many interesting effects and finds that are difficult to reproduce or detect in synthetic crystals. Herein, we investigate the photoluminescence (PL) of more than 2000 natural diamonds in the range 800–1050 nm. PL spectra were registered with excitation at 405, 450, 488 (Ar+), and 787 nm. The investigation revealed several systems that were not previously described. Some new dislocation-related systems were discovered in the spectra of crystals with signs of plastic deformation. They are four sets of doublets 890/900.3 nm, 918/930 nm, 946.5/961.5 nm, and 981/994 nm; four lines at 946, 961.5, 986, and 1020 nm. In low-nitrogen diamonds, they are accompanied by a line at 921 nm. Unreported vibronic systems with zero-phonon lines at 799.5, 819.6, 869.5, and 930 nm were revealed. In most cases, the systems were accompanied with doublet 883/885 of the simplest Ni-related center. We assigned these systems to Ni-related centers of different complexity. The results expand opportunities to restore growth conditions and thermal history of diamond crystals. The detection of new shallow centers expands the prospects of diamond as an optic and semiconductor material for applications in the NIR range.
... In the laboratory, attempts have been made to artificially induce green color in diamonds. This can be done with high-energy electron irradiation of yellowish diamonds (Collins, 1982;Wang et al., 2018), followed by prolonged annealing at a temperature of 1400°C for colorless type Ia diamonds (Collins, 2001), or using high-pressure, hightemperature (HPHT) annealing for brown type Ia diamonds (Collins et al., 2000;Collins, 2001Collins, , 2003. A multi-step processing that probably involved irra-diation, annealing, and re-irradiation was documented by GIA researchers (Fritsch et al., 1988). ...
... In the laboratory, attempts have been made to artificially induce green color in diamonds. This can be done with high-energy electron irradiation of yellowish diamonds (Collins, 1982;Wang et al., 2018), followed by prolonged annealing at a temperature of 1400°C for colorless type Ia diamonds (Collins, 2001), or using high-pressure, hightemperature (HPHT) annealing for brown type Ia diamonds (Collins et al., 2000;Collins, 2001Collins, , 2003. A multi-step processing that probably involved irra-diation, annealing, and re-irradiation was documented by GIA researchers (Fritsch et al., 1988). ...
Magallana bilineata is a euryhaline species that inhabits backwaters, creeks, estuary banks, coastal bays, and lagoons, forming oyster beds on a large scale. A large number of specimens of this species from Hab River Delta were examined to study the taxonomic characteristics of the genus Magallana as part of a joint project between Japan and Pakistan. Ten shells of each species were opened. Only one shell of M. bilineata (150 mm shell height) contained a pearl, attached to tissues near the adductor muscle. It was near-round, with a smooth surface and a purplish and off-white color very similar to the inner shell layer of M. bilineata. The crystal structure of calcium carbonate was observed under high magnification.
In this work, low-temperature photoluminescence spectroscopy was employed to investigate the N3 optical color center in natural type Ia diamond. The optical properties of the N3 center with regular changes in testing temperature and laser power were studied, and the energy level transition was also discussed. The results showed that the PL intensity of the N3 center enhanced sub-linearly with laser power increased, indicating that the electron transition of the N3 center was mainly radiative recombination with weak Auger recombination participation. In addition, the physical model was employed to analyze the change in the zero phonon line with the increase in the test temperature; it obtained thermal quenching activation energy (25.2 meV), bond softening, and strong interaction with acoustical phonons of the N3 center. The theoretical analysis of the broadening parameters revealed that the longitudinal optical phonon energy was 55.1 meV, and the electron–optic phonon coupling strength was 2.3 meV.
The formation mechanisms of the zero-phonon line optical center at 580 nm (H19 center) in photoluminescence spectra of irradiated natural diamonds and those deposited from the vapor phase were studied after their high-temperature vacuum annealing. The photoluminescence band intensity of the H19 center was shown to increase exponentially as the annealing temperature increased. Temperature dependences of photoluminescence spectra and local mechanical stress effects on the position and full width at half-height of the 580-nm zero-phonon line optical peak led to the conclusion that the H19 optical center was a complex intrinsic vacancy defect.
