Spectroscopic Investigation of Properties of Blue Sapphire Samples Depending on Heating Conditions

Phlayrahan, Aumaparn; Monarumit, Natthapong; Lhuaamporn, Thanapong; Satitkune, Somruedee; Wathanakul, P.

doi:10.1007/s10812-019-00898-y

Cited by 6 publications

(10 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The absorption peak near 3310 cm −1 was indicative of sapphire grown in a strongly reducing environment [32]. Phlayrahan et al [33] proposed the heating-induced The obvious peaks at 380 nm and 453 nm for the deep-blue core and two distinct peaks at 376 nm and 448 nm for the yellowish-brown rim in the UV-Vis absorption spectra of the studied sample were attributed to Fe 3+ -Fe 3+ ion pairs, as was the weak peak at 533 nm. The weak peak at 576 nm was caused by Fe 2+ -Ti 4+ ion pairs, which appeared at the core but not the rim (Figure 6).…”

Section: Color Genesis Of Growth Bandsmentioning

confidence: 99%

“…The absorption peak near 3310 cm −1 was indicative of sapphire grown in a strongly reducing environment [32]. Phlayrahan et al [33] proposed the heating-induced binding between Ti, Fe, and -OH in the blue sapphire structure, and that the intensity of peak at 3309 cm −1 series gradually decreases with increasing heating temperature in any given condition. However, the trend from core to rim in our sample was reversed (Figure 7), suggesting that the deep-blue rimmed by yellowish-brown bands in the investigated sample was not caused by heating but by a different redox condition during the formation.…”

Section: Color Genesis Of Growth Bandsmentioning

confidence: 99%

See 1 more Smart Citation

Genesis of Color Zonation and Chemical Composition of Penglai Sapphire in Hainan Province, China

Wang

Liu

2022

Minerals

View full text Add to dashboard Cite

The Penglai sapphires are mainly hosted in alkaline basalts and derived in alluvial sediments. Previous studies have investigated the formation of the Penglai sapphires; however, the genesis of color zoning remains ambiguous. In this paper, we report spectral and chemical composition data of sapphires using ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), and laser-ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS). The results show that the Penglai sapphire has a magmatic origin, mostly showing various shapes of incomplete girdles, barrels, and flakes. The content of Ti in rims is higher than in cores of color-banded sapphire, which results from ubiquitous Ti-bearing inclusions within grown bands. The main chromophore of the deep-blue core is Fe2+-Ti4+, which pairs with Fe3+-Fe3+, Cr3+, and V3+ in the core, likely producing purple-hued blue in an oxidizing environment. The yellowish-brown rim is due to Fe3+ and Cr3+ in a reduced environment. Compared with the basaltic sapphires worldwide, the Fe content is moderately higher than those of most Asian sapphires but obviously lower than those of Changle sapphires in Shandong, China, and overlaps with those of African sapphires.

show abstract

Section: Color Genesis Of Growth Bandsmentioning

confidence: 99%

Section: Color Genesis Of Growth Bandsmentioning

confidence: 99%

Genesis of Color Zonation and Chemical Composition of Penglai Sapphire in Hainan Province, China

Wang

Liu

2022

Minerals

View full text Add to dashboard Cite

show abstract

“…Naturally, there are many color shades of blue sapphire from milky to dark blue based on color intensity relating to the content of trace elements and internal features as well as micro-and nano-inclusion [8]. The blue intensity of blue sapphire can be changed after heat treatment [9][10][11][12][13][14][15][16] relating to the important parameters including oxidation-reduction atmospheric condition, heating temperature, soaking time and chemicals in gemstone [9].…”

Section: Introductionmentioning

confidence: 99%

“…The slight changing from Fe 2+ to Fe 3+ on blue sapphire after heating under oxidizing atmosphere at 1400 °C were proposed by linear combination fitting calculation [14]. However, the oxidation state of Fe and Ti on blue sapphire was reported as Fe 3+ and Ti 4+ before and after heating under oxidizing atmosphere no matter what temperature was used [15,16]. The causes of color change and references can be summarized in table 1.…”

Section: Introductionmentioning

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.

View full text Add to dashboard Cite

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.

show abstract

“…[4] While the band gap theory proposes that Fe in corundum always present as Fe 3+ and Fe 3+ −Ti 4+ is the cause of blue with series of experiments supporting this conclusion. [10][11][12][13][14] According to Wongkokua et al (2019), [14] the blue color is related to the energy states that (1) heating in reducing condition can cause more electron holes on the energy levels of 2.14 and 1.75 eV, thus promoting electron transitions from the corundum valence band to those mixed acceptors in the gap, and the 580 and 710 nm absorptions being raised up, i.e., more blue developed. (2) heating in oxidizing condition, electrons are added to holes on those mixed acceptors, the holes are filled up, and require less electron transition, resulting in hindering/fading of blue color.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Blue Coloration in Sapphires Using X‐Ray Absorption Near‐Edge Structure Spectroscopy (XANES)

Amphon

Chankhantha

Thammajak³

et al. 2022

Cryst. Res. Technol.

View full text Add to dashboard Cite

The color of blue sapphire has long been explained using the intervalence charge‐transfer (IVCT) [Fe2+‐Ti4+ and/or Fe2+‐Fe3+] theory, in which the blue can be reduced by thermal (heat) treatment in oxidizing condition to alter Fe2+ (FeO) to Fe3+ (Fe2O3). However, the color mechanism is not well understood. Recently, the band gap theory proposes that iron (Fe) in sapphire always presents as Fe3+, and the blue is caused by Fe3+‐Ti4+ pair, hence thermal treatment does not alter Fe oxidation. The UV–Vis–NIR, Proton‐Induced X‐ray Emission (PIXE), and X‐ray Absorption Near‐Edge Structure (XANES) techniques are carried out before and after treatment to prove this issue. The absorption spectra are slightly lower after treatment, corresponding with the reduction of blue color in all samples. XANES data reveal mixture of Fe2+ and Fe3+ (mainly Fe3+) in all samples, and show insignificantly change after heated which rather supports the band gap theory. However, calculation based on linear combination fitting (LCF) technique shows a slight change in the oxidation from Fe2+ to Fe3+ which rather supports the IVCT theory. It is noted that the highest change is found in the lowest ratio of Fe:Ti sample, while the lowest change is conversely.

show abstract

Spectroscopic Investigation of Properties of Blue Sapphire Samples Depending on Heating Conditions

Cited by 6 publications

References 12 publications

Genesis of Color Zonation and Chemical Composition of Penglai Sapphire in Hainan Province, China

Genesis of Color Zonation and Chemical Composition of Penglai Sapphire in Hainan Province, China

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

Investigation of Blue Coloration in Sapphires Using X‐Ray Absorption Near‐Edge Structure Spectroscopy (XANES)

Contact Info

Product

Resources

About