The acceptor-donor pair recombination of beryllium-treated sapphires

Monarumit, Natthapong; Lhuaamporn, Thanapong; Wathanakul, P.; Saiyasombat, Chatree; Wongkokua, Wiwat

doi:10.1016/j.radphyschem.2023.110756

Cited by 3 publications

(4 citation statements)

References 17 publications

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“…Hence, the cause of the colour change in yellow sapphires by beryllium heat treatment was proposed to be due to Fe 3+ -Be 2+ mixed-donor states [7]. Moreover, beryllium heat treatment can reduce the blue colour by acceptor-donor pair recombination between Fe 3+ -Ti 4+ mixed-acceptor states and Fe 3+ -Be 2+ mixed-donor states [12]. However, the monochromatic UV-Vis-NIR absorption spectra did not exhibit any additional features attributable to beryllium impurities within the energy band gap, as seen in the polychromatic spectra.…”

Section: Resultsmentioning

confidence: 99%

An application of polychromatic UV-Vis-NIR spectroscopy on detection of beryllium treatment in ruby and yellow sapphire

Monarumit,

Lhuaamporn,

Schwarz

et al. 2023

J. Phys.: Conf. Ser.

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The ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy has been essentially used to characterize gem materials and their treatments. The spectrophotometer was designed using a diffraction grating to provide the monochromatic light from a tungsten lamp in analyzing a sample. The signal is recorded by a photodiode, resulting in a characteristic spectrum of a gemstone sample. While the monochromatic UV-Vis-NIR spectrophotometer is used for characterizing treated ruby and yellow sapphire samples; however, some indicative characteristic absorptions could be missing. The technique may not be able to clearly differentiate the Be-treated ruby and yellow sapphire samples from the natural ones. Therefore, polychromatic UV-Vis-NIR spectroscopy could be utilized. The polychromatic light from a tungsten lamp passing through the sample provides the polychromatic UV-Vis-NIR spectrum produced by the spectrophotometer comprising a diffraction grating with a diode array CCD or CMOS detector. Both natural and Be-treated ruby and yellow sapphire samples were measured using both spectrophotometers. The experiment reveals that the polychromatic UV-Vis-NIR excitation spectroscopy can be used to differentiate the Be-treated ruby and yellow sapphires from the natural ones. Moreover, the polychromatic UV-Vis-NIR spectrophotometer offers the advantages of portability, measuring time, and low cost.

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Section: Resultsmentioning

confidence: 99%

An application of polychromatic UV-Vis-NIR spectroscopy on detection of beryllium treatment in ruby and yellow sapphire

Monarumit,

Lhuaamporn,

Schwarz

et al. 2023

J. Phys.: Conf. Ser.

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“…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%

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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“…In the fields of gemology and mineralogy, XANES spectroscopy has been employed to ascertain the oxidation states of Fe and Ti in heat-treated blue sapphire [14][15][16][17][18]34], the oxidation state of Fe in quartz [35,36], the Fe valence in beryl [37,38], and the Fe valence in heat treated spinel [39]. XANES spectroscopy is conducted using synchrotron radiation generated from a synchrotron light source radiation facility, as illustrated in Figure 3.…”

Section: X-ray Absorption Spectroscopy (Xas)mentioning

confidence: 99%

“…Recently, the proposed presence of Fe 3+ -Ti 4+ mixed acceptor states in the energy band gap has been proposed as the cause of the blue color in sapphire, suggesting that when blue sapphire is heat-treated in oxidizing conditions, electrons are added to holes on those mixed acceptors, the holes are filled up, and they require fewer electron transitions, resulting in the hindering/fading of the blue color. Therefore, the oxidation of Fe does not change in the process [14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

Amphon,

Chankhantha,

Srimuang

et al. 2024

Minerals

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Blue sapphire has long been treated with heat to modify its blue color and attain greater value. However, the process of modifying the blue color in sapphire remains not well understood. The color-changing mechanism has traditionally been explained using the Intervalence Charge Transfer (IVCT) (Fe2+-Ti4+ and/or Fe2+-Fe3+) theory, wherein the blue color can be diminished by heat treatment in an oxidizing environment which alters Fe2+ (FeO) to Fe3+ (Fe2O3) and decreases the occurrence of the IVCT process. However, recently, the band gap theory has been proposed, suggesting that iron (Fe) in sapphire is always in the Fe3+ state, the blue color is caused by Fe3+-Ti4+ pair and the heat treatment does not affect Fe oxidation state. Therefore, in this study, eight magmatic sapphires from four localities were investigated for changes in blue color via color analysis, changes in spectra using XANES, and changes in chemical composition using PIXE both before and after heat treatment. The color analysis reveals a slight reduction in saturation (fading of blue) and a noticeable lightening after heat treatment, which corresponds with the high content of solid inclusions or trapiche samples. XANES data analysis using the LCF technique indicated insignificant changes in Fe oxidation state from 2+ to 3+ after heat treatment across all samples. However, when comparing the XANES data with color parameter L*a*b*, it is noted that the percentage of Fe oxidation state changes does not show a positive relationship with changes in blue based on color parameter b* (blue–yellow); rather, it shows a positive relationship with parameter L* (lightness). Microscopic observations also reveal the dissolution of clouds or minute particles around planes of ilmenite needles. It could be suggested that the changes in Fe oxidation state may not be directly related to changes in blue color but could be linked to the partial dissolution of Fe-bearing inclusions.

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The acceptor-donor pair recombination of beryllium-treated sapphires

Cited by 3 publications

References 17 publications

An application of polychromatic UV-Vis-NIR spectroscopy on detection of beryllium treatment in ruby and yellow sapphire

An application of polychromatic UV-Vis-NIR spectroscopy on detection of beryllium treatment in ruby and yellow sapphire

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

Changes in Blue Color of Sapphire Compared with Oxidation State Changes

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