Oxidation states of Fe and Ti in blue sapphire

Wongrawang, P; Monarumit, Natthapong; Thammajak, Nirawat; Wathanakul, P.; Wongkokua, Wiwat

doi:10.1088/2053-1591/3/2/026201

Cited by 24 publications

(16 citation statements)

References 17 publications

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“…For example, titanium and iron impurities turn the crystal blue. It is generally believed that that the blue color is caused by intervalence electron transfer of the red-light absorbing Fe–Ti pairs. − However, alternative mechanisms were suggested. , Moreover, the oxidation states of the ground-state Fe–Ti pair are still debated. , Here, we apply the OS-CDFT method to provide insights into this photoexcited intervalence electron transfer process.…”

Section: Resultssupporting

confidence: 91%

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Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Sit

2019

J. Chem. Theory Comput.

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We propose a new constrained density functional theory (CDFT) approach which directly controls the oxidation state of the target atoms. In this new approach called oxidation-state constrained density functional theory (OS-CDFT), the eigenvalues of the occupation matrix obtained from projecting the Kohn–Sham wave functions onto the valence orbitals are constrained to obtain the desired oxidation states. This approach is particularly useful to study electron transfer problems in transition metal-containing systems due to the multivalent nature of the transition metal ions. The calculation of the forces on the ions and of the coupling constant was implemented under the OS-CDFT scheme to allow efficient and accurate study of electron transfer reactions. We demonstrated the application of this method in the study of different electron transfer reactions including the aqueous ferrous–ferric self-exchange reaction, polaron hopping in the TiO2 anatase and bismuth vanadate, and photoexcited electron transfer in the sapphire.

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Section: Resultssupporting

confidence: 91%

“…This explains the distinct blue color of the corundum crystal with Fe–Ti pair impurities. This is also in reasonable agreement with the 580–710 nm absorption range found in the photoluminescence experiments of the blue sapphire. , …”

Section: Resultssupporting

confidence: 91%

Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Sit

2019

J. Chem. Theory Comput.

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“…MMCT is well documented in the literature. The intense blue color of sapphire has been proposed as arising from Fe → Ti MMCT among trace Ti 4+ and Fe 2+ ions in the Al 2 O 3 crystal. , Transition-metal tungstate complexes, MWO 4 (M = Mn, Co, Ni, and Cu), exhibit MMCT from the occupied t 2g states on M to empty W 5d orbitals . Photosensitization of nanocrystalline TiO 2 was achieved by chemisorption of pentacyanothiamine-ferrate(II) that formed a surface complex characterized by a Fe II → Ti IV MMCT .…”

Section: Resultsmentioning

confidence: 99%

Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO₂ Nanorods

et al. 2018

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We report the sequential, quantitative loading of transition-metal ions (Cr, Mn, Fe, Co, Ni, and Cu) onto the surface of rod-shaped anatase TiO nanocrystals in bimetallic combinations ( C = 15) to form M,M'-TiO nanocrystals. The materials were characterized with transmission electron microscopy (TEM), powder X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. TEM and XRD data indicate that the sequential adsorption of metal ions occurs with the retention of the phase and morphology of the nanocrystal. Atomistic models of the M,M'-TiO nanocrystals were optimized with density functional theory calculations. Calculated UV-visible absorption spectra and partial charge density maps of the donor and acceptor states for the electronic transitions indicate the importance of metal-to-metal charge transfer (MMCT) processes.

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“…Thus, an intervalence charge transfer between Ti 3+ and Fe 3+ was the underlying dominant mechanism postulated for the blue colouration of the sapphires [13] that produced the metastable Fe 2+ /Ti 4+ configuration [17]. Recently, based on X-ray absorption nearedge structure (XANES) spectra, the energy band model of Fe 3+ -Ti 4+ mixed acceptor states was formulated to describe the cause of the colour of blue sapphire [21].…”

Section: Colourmentioning

confidence: 99%

“…They have significant, pronounced colour zoning and extend to 10 cm in diameter. One Table 4 Selected important deposits of rubies ( O ) and sapphires ( O ) across the world [81] Marbles Amphibolites [91] O [21] Thailand…”

Section: Corundum As a Gemstonementioning

confidence: 99%

Intriguing minerals: corundum in the world of rubies and sapphires with special attention to Macedonian rubies

et al. 2021

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This lecture text presents features of the fascinating mineral corundum and its gem varieties, ruby and sapphire. The geologic occurrences of its varieties and the best-known world localities are presented in detail. The mineralogy and crystallography of corundum, as well as its occurrence forms, are discussed. The origin of their colour varieties and their usage are described, in addition to their important physical characteristics. Applications in the watch and laser industries and as an abrasive material, among others, are included. The ruby variety from dolomite marble in North Macedonia exhibits the unique optical phenomenon known as diasporescence-the inclusion of diaspore crystals in the corundum matrix. This phenomenon affects the parting of corundum crystals and influences their colour, density and hardness. Therefore, special attention is paid here to morphological and physical characteristics of the Macedonian gem corundum.

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Oxidation states of Fe and Ti in blue sapphire

Cited by 24 publications

References 17 publications

Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO₂ Nanorods

Intriguing minerals: corundum in the world of rubies and sapphires with special attention to Macedonian rubies

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Oxidation states of Fe and Ti in blue sapphire

Cited by 24 publications

References 17 publications

Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Oxidation-State Constrained Density Functional Theory for the Study of Electron-Transfer Reactions

Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO2 Nanorods

Intriguing minerals: corundum in the world of rubies and sapphires with special attention to Macedonian rubies

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Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO₂ Nanorods