Browsing by Author "Chan, T. S."

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Effect of Mn substitution on electronic structure of Ca(9)Y(PO(4))(7):Eu(2+), Mn(2+) phosphor determined by X-ray absorption spectroscopy
(2011-10-27)
Lu, Y. R.
;
Huang, C. H.
;
Chen, T. M.
;
Lin, J. H.
;
Ma, Y. R.
The single-composition Ca(9)Y(PO(4))(7):Eu(2+), Mn(2+) phosphors were synthesized by a solid-state reaction. The luminescent properties and electronic structures were investigated by photoluminescence (PL) and X-ray absorption near-edge structure (XANES). The PL demonstrated energy transfer and a red-shift as the Mn doping level was increased. The energy transfer is ascribed to charge transfer between Eu and Mn. The change of the PL intensity is caused by the increased O 2p-Mn 3d hybridization. The narrowing of the band gap, which finding is supported by the red-shift, is responsible for the formation of the Mn-related states close to the conduction band minimum. (C) 2011 Elsevier B.V. All rights reserved.
Effect of Mn substitution on electronic structure of Ca9Y(PO4)(7):Eu2+, Mn2+ phosphor determined by X-ray absorption spectroscopy
(2011-10-27)
Lu, Y. R.
;
Huang, C. H.
;
Chen, T. M.
;
Lin, J. H.
;
Ma, Y. R.
The single-composition Ca9Y(PO4)(7):Eu2+, Mn2+ phosphors were synthesized by a solid-state reaction. The luminescent properties and electronic structures were investigated by photoluminescence (PL) and X-ray absorption near-edge structure (XANES). The PL demonstrated energy transfer and a red-shift as the Mn doping level was increased. The energy transfer is ascribed to charge transfer between Eu and Mn. The change of the PL intensity is caused by the increased O 2p-Mn 3d hybridization. The narrowing of the band gap, which finding is supported by the red-shift, is responsible for the formation of the Mn-related states close to the conduction band minimum. (C) 2011 Elsevier B.V. All rights reserved.
Pressure-induced structural distortion of TbMnO(3): A combined x-ray diffraction and x-ray absorption spectroscopy study
(2009-04-01)
Chen, J. M.
;
Chou, T. L.
;
Lee, J. M.
;
Chen, S. A.
;
Chan, T. S.
The variation of electronic states and structural distortion in highly compressed multiferroic TbMnO(3) was probed by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. Refined XRD data enabled observation of a reduced local Jahn-Teller (JT) distortion of Mn sites within MnO(6) octahedra in TbMnO(3) with increasing hydrostatic pressure. A progressively increasing intensity of the white line in Mn K-edge x-ray absorption spectra of TbMnO(3) was detected with increasing pressure. The absorption threshold of Mn K-edge spectra of TbMnO(3) is shifted toward higher energy, whereas the pre-edge peak is slightly shifted to lower energy with increasing hydrostatic pressure. We provide spectral evidence for pressure-induced bandwidth broadening for mangnites. The enhanced intensity of the white line and the shifted absorption threshold of Mn K-edge spectra are explained in terms of a reduced JT distortion of MnO(6) octahedra in compressed TbMnO(3). Comparison of XAS data with full-multiple-scattering calculations using code FDMNES shows satisfactory agreement between experimental and calculated Mn K-edge spectra.
Pressure-induced structural distortion of TbMnO3: A combined x-ray diffraction and x-ray absorption spectroscopy study
(2009-04-01)
Chen, J. M.
;
Chou, T. L.
;
Lee, J. M.
;
Chen, S. A.
;
Chan, T. S.
The variation of electronic states and structural distortion in highly compressed multiferroic TbMnO3 was probed by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. Refined XRD data enabled observation of a reduced local Jahn-Teller (JT) distortion of Mn sites within MnO6 octahedra in TbMnO3 with increasing hydrostatic pressure. A progressively increasing intensity of the white line in Mn K-edge x-ray absorption spectra of TbMnO3 was detected with increasing pressure. The absorption threshold of Mn K-edge spectra of TbMnO3 is shifted toward higher energy, whereas the pre-edge peak is slightly shifted to lower energy with increasing hydrostatic pressure. We provide spectral evidence for pressure-induced bandwidth broadening for mangnites. The enhanced intensity of the white line and the shifted absorption threshold of Mn K-edge spectra are explained in terms of a reduced JT distortion of MnO6 octahedra in compressed TbMnO3. Comparison of XAS data with full-multiple-scattering calculations using code FDMNES shows satisfactory agreement between experimental and calculated Mn K-edge spectra.
Structural distortion and electronic states of Rb doped WO3 by X-ray absorption spectroscopy
(2016-01-01)
Wang, Y. C.
;
Hsu, C. H.
;
Hsu, Y. Y.
;
Chang, C. C.
;
Dong, C. L.
Rubidium tungsten bronzes (RbxWO3) have recently attracted much attention due to their intriguing phenomena, such as complex structural phase transitions, strong electron-phonon coupling, and superconducting properties. This study investigates the local atomic and electronic structures of RbxWO3 (0.17 <= x <= 0.33). X-ray powder diffraction patterns showed a hexagonal tungsten bronze (HTB) phase. X-ray absorption spectra (XAS) at the W L-3-edge and Rb K-edge of RbxWO3 were carried out. The XAS analysis indicated a local distorted WO6 octahedron which leads to a splitting of e(g) and t(2g) energy states in the tungsten 5d orbital and this splitting of energy levels exhibited an asymmetrical behavior at x = 0.23 and 0.27. Overall analysis revealed a distortion of local atomic structure of the WO6 octahedra by rubidium doping, leading to the modification of the electronic structures of e(g) and t(2g) states in the tungsten 5d orbital, thereby accounting for the property changes in CDW formation and superconducting transition temperature of these materials.