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The electronic structure and optical properties of bulk, micro-sized, and nano-sized α-Al2O3 (wafer, microparticles (MPs), nanowires (NWs), and nanotubes (NTs)) have been investigated using X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). XANES results show that the wafer, MPs, and NTs have characteristic features of α-Al2O3. The NWs have a core/shell structure with a single crystalline α-Al2O3 core surrounded by an amorphous shell, which is consistent with transmission electron microscopy result. It is found that some Al3+ in the shell and core/shell interface of the NWs as well as the surface of the NTs were reduced to Al2+ or Al1+ during the growth process. XEOL results show that the wafer and MPs have a broad emission at 325 nm and a sharp emission at 694 nm, which are attributed to F+ center and Cr3+ impurities, respectively. The NWs exhibit an intense emission at 404 nm that comes from F center, while the NTs show relatively weak luminescence at 325, 433, and 694 nm, which are attributed to F+ center, F center, and Cr3+ impurities, respectively. The O K-edge XEOL confirms that the emissions of α-Al2O3 in the range of 250-550 nm are related to the oxygen site. Furthermore, on the basis of XEOL and photoluminescence yield, the strong luminescence of the NWs (404 nm) is related to the Al2+ or Al1+ in the shell and core/shell interface, while the luminescence of the NTs at 325 and 433 nm are related to the bulk and the Al2+ or Al1+ on the surface, respectively. [ABSTRACT FROM AUTHOR]

The reductive dehalogenation of a zwitterionic GeII species to make a zwitterionic GeI dimer with a 1,2‐dicationic core is reported herein. To the root of the stability of this compound, the molecular and electronic structures were comprehensively characterized and investigated using crystallographic, spectroscopic, and computational methods. It was determined that the Ge centers are attracted because they are both electron‐rich and positively charged. A comparison to the electronic structure in triphosphenium cations revealed varying degrees of covalent bonding and that this difference can be distinguished spectroscopically. [ABSTRACT FROM AUTHOR]

We report a resonant inelastic x-ray scattering (RIXS) study of crystalline CeB6. Ce Lα1,2 RIXS was measured with excitation energies resonant with the Ce L3-edge. A lifetime-broadening suppressed x-ray absorption near-edge structure (LBS-XANES), which successfully reproduced the Lα1,2 RIXS spectra over wide ranges of excitation and emission energies, was simulated using the SIM-RIXS program. A pre-edge structure in the LBS-XANES can be resolved, and many-body effects were suggested in the Lα1,2 RIXS around the Ce L3-edge energy. No convincing signs of Ce (II) or Ce (IV) states were observed in the LBS-XANES. Ce Lγ4 RIXS was measured at 302 K and 28 K with excitation energies across the Ce L1-edge. The interactions of p-valence electrons between Ce and B6 were found to be considerably small, regardless of temperature. Thus, the electronic state of CeB6 was concluded to be suitably described as a nominally Ce(4f 1)3+(e-)(B6)2- system with some hybridization among all valence orbitals of Ce and B. [ABSTRACT FROM AUTHOR]

Electronic structures of Se, Se80Te20, and Se80-xSbxTe20(0≤x≤9) systems have been investigated using x-ray photoelectron spectroscopy and x-ray absorption near edge spectroscopy (XANES). The experimental results show strong Se–Se and Se–Te interaction as well as antimony dilution effects in the ternary alloy. The interpretation of the results is assisted by theoretical calculations. The densities of states for the energy bands have been evaluated with the full potential augmented plane wave method based on the density functional theory (DFT) and the real-space multiple scattering (RSMS) approach using small clusters of model crystal structures. The ab initio calculation methods for the XANES spectra of Se, Se80Te20, and Se80-xSbxTe20(0≤x≤9) systems are compared with the experimental data. It is found that the DFT calculation provides better agreement with the pre-edge resonance, while RSMS yields good agreement with the postedge region. The interplay of x-ray spectroscopy results and theory is discussed. [ABSTRACT FROM AUTHOR]

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We present the first report for the investigation on surface second harmonic generation (SSHG) of thin films of Se80−xSbxTe20 (0 ≤ x ≤ 9 at.%) system. SSHG measurements were made using a confocal microscope system and a mode locked Ti:Saphire pulsed laser (785 nm) probe beam with 100 fs pulses. A remarkable difference in the magnitude of the signal generated between the samples with antimony content ≤4 at.% and those containing antimony >4 at.% has been explained based on charge distribution associated with structural changes in these materials for different compositions. The results have been discussed on the basis of relatively isolated atomic events that occur at short length scales mainly due to spatial redistribution of covalent bonds and the rational changes in the electric dipole moment arising from the change in the distribution of the lone pair electrons inherent in chalcogenide glasses. The analysis of the results is supported by the variation of the glass transition temperature obtained from differential scanning calorimetry (DSC) results. The electronic structure has been calculated using the density functional theory (DFT) modified by the generalized gradient approximation (GGA) for the exchange correlation energy. [ABSTRACT FROM AUTHOR]

Abstract: High resolution X-ray absorption near-edge structures (XANES) of rare earth hexaboride (LaB6 and CeB6) single crystals have been studied at the regions of the B K-edge and the La and Ce N5,4-edge. The difference in the occupancy of 4f electrons between the ground state of La (4d104f0) and Ce (4d104f1) causes different features in the La and Ce N5,4-edge XANES (giant resonance), while B K-edge XANES exhibit similar features for the two materials indicating that the influence of the 4f electron is confined in the vicinity of the lanthanide ion. Theoretical simulations based on density functional theory using the WIEN2k code have been conducted to compare with the XANES at B K-edge. The results and their implications are discussed. [Copyright &y& Elsevier]

The in-depth mechanism of the emerging Ru-catalyzed polyolefin hydrogenolysis remains unclear. Here, we overcome this challenge by constructing a strong metal-support interaction (SMSI) system based on Ru/TiO 2 catalysts. With the increase of SMSI intensity, electrons are transferred from the TiO x capping layer to the Ru species. This effect facilitates the key steps of hydrogenation/desorption, while having little effect on the dehydrogenation and C–C cracking elementary reactions. As a result, the catalyst with higher hydrogenation capability prone to proceed hydrogenation and desorption step, thus suppressing cascade C–C cracking and avoiding the production of low value methane. The catalyst with the strongest SMSI effect exhibits a liquid fuel yield of 89.4% at ∼100% solid conversion. The SMSI effect also enables the catalysts with superior stability, so it can also efficiently upcycle commercial polyolefins. This work provides an in-depth understanding of the effects of metal-support interactions on polyolefin hydrogenolysis and paves the way for catalyst design. [Display omitted] • This work provides a comprehensive mechanism study of polyolefin hydrogenolysis. • Electron-rich Ru species facilitate the hydrogenation and desorption processes. • We achieve a ∼90% yield of value-added liquid fuels and a low gas yield (8.6%). [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure and the origin of luminescence from blue luminescent carbon nanocrystals (CNC) have been investigated with X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL). XANES shows that nitrogen has been incorporated into the carbon nanocrystals matrix (dominated by sp2 carbon). XEOL from CNC is compared with that from natural diamond and previously reported CVD nanodiamond containing N impurities. The results reveal that N doping is almost certainly responsible for the blue luminescence in carbon nanocrystals. The implication of the results is discussed. [Copyright &y& Elsevier]