Study of Fe ions in aquamarine and the effect of dichroism as seen using UV–Vis, NIR and x-ray

Bunnag, Nantharat; Kasri, Bootsaba; Setwong, Watcharakon; Sirisurawong, Ekkasit; Chotsawat, Maneerat; Chirawatkul, Prae; Saiyasombat, Chatree

doi:10.1016/j.radphyschem.2020.109107

Cited by 15 publications

(12 citation statements)

References 18 publications

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“…Site symmetry of Fe such as coordination environments and Fe oxidation state could be obtained from the pre-edge fit considering from characteristics of pre-edge features [22,29]. In this study, before heating found that trend of the integrated intensity of sapphire from Sri Lanka is higher than in Kanchanaburi province, Thailand, which tends to be in the center as shown in figure 8(a).…”

Section: Resultsmentioning

confidence: 69%

“…After that, advanced gemological instruments were applied to the samples consisting including EDXRF spectrophotometer to analyze the chemical composition [18], the internal features focused on types of mineral inclusions of the samples were observed beneath gems microscope by Laser-Raman spectroscopy as well as the micro inclusions were observed by SEM-EDS [8], the absorption spectra of the samples that related with the cause of color on blue sapphire before and after heating were determined by UVvis-NIR spectrophotometer [19], FTIR spectrometer was used for analyzing the functional group in molecule i.e., C-H C-O and O-H [15] and XAS technique was focused on Fe K-edge and Ti K-edge XANES spectra to determine Fe and Ti oxidation state [7,15,16]. The data from XAS spectra were analyzed by Athena for determining the Fe and Ti oxidation states [20] and Larch software for studying the site symmetry of Fe by characteristics of pre-edge features [21,22]. Moreover, the energy band gaps (E g ) of the samples were calculated using a Tauc plot diagram [23].…”

Section: Methodsmentioning

confidence: 99%

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The blue color mechanism on sapphires from different gem deposits before and after heating under oxidizing atmosphere

Thengthong,

Sakkaravej,

Wongkokua

et al. 2023

J. Phys. Commun.

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The blue color of sapphire is commonly related to the amount of Fe and Ti impurities replacing Al3+ in Al2O3 structure. Generally, the color intensity on sapphires is related to the gem deposits including the basaltic-related and metamorphic-related ones. The color of sapphires has been changed after heating under oxidizing atmosphere. However, the explanation about the color mechanism from some previous research contradicted each other and it was still wondered. For this reason, this research is focused on the role of Fe and Ti oxidation states as well as the blue color mechanism on sapphires before and after heating under oxidizing atmosphere. In this study, the sapphire samples were collected from different gem deposits including basaltic-related sapphires from Kanchanaburi province, Thailand and metamorphic-related ones from Sri Lanka before and after heating at 1100°C under oxidizing atmosphere. As a result, the blue color on sapphires before heating can be described that a hole color center assigned to Fe3+-Ti4+ mixed acceptor states inside an energy band gap that could be received an electron from the valence band for charge-balancing after excitation. After heating, the basaltic-related sapphires turned from dark blue to light blue and the metamorphic-related ones turned from light blue to colorless because the Fe3+-Ti4+ mixed acceptor states were decreased because a hole color center was filled by an electron from oxygen during the heating process instead of an electron from the valence band. Therefore, it can be concluded that the blue color mechanism on sapphires before and after heating under oxidizing atmosphere can be explained by an energy band model involving the presence or absence of Fe3+-Ti4+ mixed acceptor states as well as a hole color center inside an energy band gap.

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Section: Resultsmentioning

confidence: 69%

Section: Methodsmentioning

confidence: 99%

The blue color mechanism on sapphires from different gem deposits before and after heating under oxidizing atmosphere

Thengthong,

Sakkaravej,

Wongkokua

et al. 2023

J. Phys. Commun.

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“…The original spectrum signal was analyzed and the peaks were fitted to four main peaks: 280 nm, 380 nm, 482 nm, and 542 nm. The peak at 280 nm was assigned to Fe (III) and confirmed the existence of Fe 2 O 3 and MgFe 2 O 4 [35,36]. The peak at 380 nm was assigned to Cr (III) [37], which corresponds to the FeCr 2 O 4 phase.…”

Section: Direct-acid-leaching Processmentioning

confidence: 64%

Efficient Recovery of Vanadium from High-Chromium Vanadium Slag with Calcium-Roasting Acidic Leaching

Peng

Shi

et al. 2022

Minerals

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High-chromium vanadium slag (HCVS) is an important by-product generated during the smelting process of high-chromium-vanadium-titanium-magnetite. Direct acid leaching and calcium-roasting acid leaching technology were applied to recover vanadium and chromium from HCVS. The effects of experimental parameters on the leaching process, including concentration of H2SO4, reaction temperature, reaction time, and liquid-to-solid ratio, were investigated. The XRD and UV-Vis DRS results showed that vanadium and chromium existed in low valence with a spinel structure in the HCVS. The Cr-spinel was too stable to leach out; no more than 8% of the chromium could be leached out both in the direct acid leaching process and calcium-roasting acid-leaching process. Most low valence vanadium could be oxidized to high valence with calcium-roasting technology, and the leaching efficiency could be increased from 33.89% to 89.12% at the selected reaction conditions: concentration of H2SO4 at 40 vt.%, reaction temperature of 90 °C, reaction time of 3 h, liquid-to-solid ratio of 4:1 mL/g, and stirring rate of 500 rpm. The kinetics analysis indicated that the leaching behavior of vanadium followed the shrinking core model well, and the leaching process was controlled by the surface chemical reaction, with an Ea of 58.95 kJ/mol and 62.98 kJ/mol for direct acid leaching and roasting acid leaching, respectively.

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“…The spectrum ( Figure 3 ) shows two main absorption bands at 425 nm, due to Fe 3+ in octahedral sites, and at ca. 820 nm, due to Fe 2+ -Fe 3+ intervalence charge transfer [ 25 ].…”

Section: Resultsmentioning

confidence: 99%

The Use of UV-Visible Diffuse Reflectance Spectrophotometry for a Fast, Preliminary Authentication of Gemstones

et al. 2022

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The identification of gemstones is an important topic in the field of cultural heritage, given their enormous value. Particularly, the most important precious stones, namely diamond, emerald, ruby and sapphire, are frequently subjected to counterfeit by substitution with objects of lesser value with similar appearance, colour or shape. While a gemmologist is able to recognise a counterfeit in most instances, more generally, it is not easy to do this without resorting to instrumental methods. In this work, the use of UV-visible diffuse reflectance spectrophotometry with optic fibres (FORS) is proposed as a fast and easy method for the preliminary identification of gemstones, alternative to the classical methods used by gemmologists or to Raman spectroscopy, which is by far the instrumental method with the best diagnostic potential, but it cannot be used in situations of problematic geometric hindrance. The possibilities and the limitations given by the FORS technique are critically discussed together with the spectral features of the most important gemstones. Finally, the application of chemometric pattern recognition methods is described for the treatment of large sets of spectral data deriving from gemstones identification.

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Study of Fe ions in aquamarine and the effect of dichroism as seen using UV–Vis, NIR and x-ray

Cited by 15 publications

References 18 publications

The blue color mechanism on sapphires from different gem deposits before and after heating under oxidizing atmosphere

The blue color mechanism on sapphires from different gem deposits before and after heating under oxidizing atmosphere

Efficient Recovery of Vanadium from High-Chromium Vanadium Slag with Calcium-Roasting Acidic Leaching

The Use of UV-Visible Diffuse Reflectance Spectrophotometry for a Fast, Preliminary Authentication of Gemstones

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