Microstructure and crystallization properties of TeO2?PbF2 glasses

The microstructures of (1 − x)(TeO₂)–xPbF₂, (x = 0.1, 0.15, and 0.25 mol) glasses were investigated by using the Raman spectroscopic technique. The effect of compositions on the TeO₂ glass networks and the intensity ratios of the deconvoluted Raman peaks were determined. The results confirm that the addition of modifiers to the glass network former shifts the Raman intensity and the peak wavenumber values for each band in the 167–165, 652–645, and 747–755 cm⁻¹ wavenumber regions. The structural evaluation was recognized from the Raman spectra, with the structural units described as [TeO₃₊₁] polyhedra, [TeO₃] trigonal pyramids, and [TeO₄] trigonal bipyramids for this binary glass system. Heat‐treatment of the samples shows that the metastable crystalline phase of TeO₂ known as γ‐TeO₂ is formed only when the modifier content is 10 mol% in the glass matrix. Transparent glass properties were not realized when the TeO₂ amount was decreased to less than 10 mol% content. Copyright © 2008 John Wiley & Sons, Ltd.     

Computational characterization of the hydroxylamino (?NH?OH) group

We have examined computationally some properties of the hydroxylamino group, ? N(H)? OH, in different molecular environments. Geometries were optimized at the B3LYP/6‐31G** level and used to calculate B3LYP/6‐311G(3df,2p) energy differences and HF/6‐31G* electrostatic potentials V( r ) and local ionization energies . V( r ) and were evaluated on the molecular surfaces defined by the 0.001 au contours of the electronic densities. Two important factors in determining the ? N(H)? OH structure are lone pair repulsion and possible intramolecular hydrogen bonding involving the remainder of the molecule, which can affect the pyramidal character of the nitrogen. The nitrogen and oxygen lone pairs produce regions of negative potential, those of the oxygen being stronger. These should function as hydrogen bond acceptors, although not as well as NH₃ and H₂O. The nitrogen lone pairs, although less negative, are expected to be the more basic, often roughly similar to pyridine. The amine and hydroxyl hydrogens tend to have quite positive potentials, and should be potent in hydrogen bonding. Depending upon the remainder of the molecule, the hydroxyl and the amine protons can range from essentially no acidity to weak to quite strong. The hydroxylamino group is estimated to have an average polarizability of 2.38 ų and as a substituent on aromatic rings to be activating and ortho, para‐directing, with Hammett δ_p = ?0.37. Copyright © 2007 John Wiley & Sons, Ltd.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Modeling the physico‐chemistry of acid sulfate waters through Raman spectroscopy of the system FeSO4?H2SO4?H2O

Mine waters containing extremely high concentrations of sulfuric acid and dissolved iron are found in the Rio Tinto (Spain) area. In this study, Raman spectroscopy has been used to investigate the speciation of the system iron(II)–sulfuric acid–water as an approach to study Rio Tinto's stream water. Several solutions of aqueous sulfuric acid containing iron(II) sulfate in the range 0–1.65 mol/kg were prepared, and qualitative and quantitative analyses of the ions present in the solutions were carried out using Raman spectroscopy. The intrinsic features of Raman spectroscopy allowed the identification of the species present in solution and calculation of the species concentration through band‐fitting of the Raman spectra. The activity coefficient product of the system iron(II) sulfate–sulfuric acid–water as a function of salt concentration is reported. Previous findings on the formation of iron(II) hexahydrate complexes in the mentioned system have been corroborated by means of Raman spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

C?H hydrogen bonding: 3. Hammett correlations for phenylacetonitriles and tetrafluorobenzenes with HMPA

Understanding the hydrogen bond, or H‐bond, arguably the strongest known intermolecular attractive force, is of great importance. Models of H‐bonding hold that both electrostatic and covalent components are at work. H‐bonding of C? H bonds, and thus presumably other A? H bonds, is greatly facilitated by polar substituents. We have found that equilibrium constants, K, for C? H H‐bonding in series of phenylacetonitriles and tetrafluorobenzenes with HMPA are closely correlated by the Hammett equation. That is, K values vary as substituents of different polarities are introduced at positions remote from the donor C? H bond. This result is consistent with a significant electrostatic component in these examples of H‐bonding. It may, however, also be explained by interaction with the σ* orbital of the C? H bond, which is involved in the covalent component of the H‐bond. Theoretical models need to be applied to this and other cases. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy in living plant using triplex Au?Ag?C core–shell nanoparticles

This paper presents, for the first time, noninvasive imaging of a livingplant using biocompatible carbon‐encapsulated Au Ag nanoparticles (NPs) using micro‐Raman spectroscopy (MRS). A convenient and controllable hydrothermal synthetic route was developed to synthesize the layer‐by‐layer triplex Au Ag C core–shell NPs, which can incorporate the reporter molecule 4‐mercapto benzoic acid (4‐MBA). A unique approach was devised to deliver the carbon‐encapsulated surface‐enhanced Raman scattering (SERS) tags into the leaf of Nicotiana benthamiana. In vivo SERS mapping was subsequently performed to monitor the distribution of tags inside the leaf, which successfully avoided interference of autofluorescence from plant tissue. The imaging modality reported here and further the bio‐functionalized carbon‐encapsulated SERS NPshold significant potential as a strategy forbiochemical imaging in living plantsin a noninvasive and nontoxic manner, whichmight open up exciting opportunities for plant sciences. Copyright © 2010 John Wiley & Sons, Ltd.     

Broadband ∼2μm emission in Tm3+/Ho3+ co-doped TeO2–WO3–La2O3 glass

In this work, we report the infrared emission properties of Tm³⁺/Ho³⁺ co-doped TeO₂–WO₃–La₂O₃ (TWL) glass under 808 nm laser excitation. A broad and flat emission from 1600 to 2200 nm corresponding to the Tm³⁺ (³F₄→³H₆) and Ho³⁺ (⁵I₇→⁵I₈) emissions is observed. The full width at half maximum (FWHM) of this broadband increases up to a value of ～370 nm with an optimal [Tm³⁺]/[Ho³⁺] concentration ratio. The energy transfer processes of Tm³⁺?Ho³⁺ are analyzed and the results show that energy transfer between Tm³⁺ and Ho³⁺ plays an important role in the luminescence mechanism. The OH^? influence on the broadband emission is also discussed. These results indicate that Tm³⁺–Ho³⁺ co-doped TWL glass could be a promising material for widely tunable laser or broadband amplifier applications.     

Raman scattering of MnOx?CeOx composite catalysts: structural aspects and laser‐heating effects

Composite MnO_x CeO_x catalysts (Mn_at: Ce_at = 1) synthesized via the redox and coprecipitation routes were comparatively characterized by micro‐Raman spectroscopy using a laser irradiation power ranging between 0.6 and 4.2 mW. A quasi‐molecular dispersion of the oxide species determines a major and irreversible structural rearrangement of the redox MnO_x CeO_x system because of severe heating effects for laser power in excess of 0.6 mW. The X‐ray diffraction data of samples calcined in the range of 673 1273 K confirm that the micro‐Raman characterization of the composite MnO_x CeO_x systems requires an adequate minimization of the irradiation power to prevent the strong sintering and restructuring phenomena due to laser‐heating effects. Copyright © 2011 John Wiley & Sons, Ltd.     

C?H bond activation of ethylene by bare neutral palladium and platinum atoms: a theoretical investigation

The reactions of bare neutral palladium (Pd) and platinum (Pt) atoms with ethylene on both singlet and triplet surfaces were investigated at B3LYP and CCSD (T) levels of theory. The calculated potential energy profiles clearly show that Pt has higher reactivity than Pd toward ethylene. For both Pd and Pt, the reactions on singlet surfaces are energetically more favorable than those on triplet surfaces. However, notable barriers lie on the singlet and triplet surfaces for Pd +ethylene. This result rationalizes the experimental observation that Pd mainly forms π‐complex with ethylene. But under high‐energy condition, the reaction can proceed to yield dehydrogenation products, Pd‐CCH. and Pd (HCCH). For Pt, triplet‐singlet surface crossing was suggested to occur in the region where Pt forms π‐complex with ethylene to lead the reactions to the energetically more favorable singlet surfaces. For both the two metals, π‐complex and C? H bond insertion species are the reaction intermediates and the H.‐elimination products are the final products. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of charge-compensated C3v (Ⅱ) centers for Er3+ ions in CdF2 and CaF2 crystals

A unified theoretical method is established to determine the charge-compensated C3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 crystals by simulating the electron paramagnetic resonance(EPR)parameters and Stark energy levels.The potential(Er³⁺–F^?–O₄^2?)and(Er³⁺-F₇^?-O₄^2?)structures for theC3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 crystals are checked by diagonalizing 364×364 complete energy matrices in the scheme of superposition model.Our studies indicate that the C3v(Ⅱ)centers of Er3+ions in CdF2 and CaF2 may be ascribed to the local(Er³⁺-F^?-O₄^2?)structure,where the upper ligand ion F?undergoes an off-center displacement by?Z≈0.3?A for CdF2 and?Z≈0.29?A for the CaF2 along the C3 axis.Meanwhile,a local compressed distortion of the(ErFO4)6?cluster is expected to be?R≈0.07?A for CdF2:Er3+and?R≈0.079?A for CaF2:Er3+.The considerable g-factor anisotropy for Er3+ions in each of both crystals is explained reasonably by the obtained local parameters.Furthermore,our studies show that a stronger covalent effect exists in the C3v(Ⅱ)center for Er3+in CaF2 or CaF2,which may be due to the stronger electrostatic interaction and closer distance between the central Er3+ion and ligand O2?with the(Er³⁺-F^?-O₄^2?)structure.     

GeO2-Bi2O3-MOx(MOx=WO3,BaO)玻璃近红外超宽带发光的研究

(99.5-χ)GeO2-XBaO-0.5Bi2O3(χ=3,6,9mol%)与(99.5-(4))GeO2-(4)WO3-0.5Bi2O3((4)=3,6,9mol%)玻璃,测定了样品的发射光谱(800 nmLD激发)、吸收光谱、荧光衰减和差热曲线.实验结果表明,在GeO2-.WO3-Bi2O3系统玻璃中,随着WO3含量的增加,在1260 nm处的发光强度增强,荧光半高宽(FWHM)增宽,荧光寿命增长,而且玻璃的吸收边带发生明显的红移;在GeO2-BaO-Bi2O3系统玻璃中,随着BaO含量的增加,玻璃在1290 nm处发光强度增强,FWHM增宽,荧光寿命增长,吸收边带也有明显的红移.从吸收边带发生红移的情况,结合发射光谱和荧光衰减曲线特性,我们推断玻璃样品在近红外的宽带发光可能由Bi5+离子所引起.从荧光特性估算了玻璃的σ×τ和σp×△λ值,这些玻璃均具有较小的σp×τ和较大的σ×△λ特性,说明GeO2-Bi2O3-MOx(MOx=WO3,BaO)系统玻璃是研制成近红外(O到S波段)超宽带光纤放大器的良好材料.     

Investigation of a high-temperature phase of 3Bi2O3·2TeO2 binary oxide

The high-temperature phase of 3Bi₂O₃·2TeO₂ binary oxide is characterized by thermal analysis, X-ray powder diffraction, and¹²⁵Te Mössbauer spectroscopy. The phase, obtained by rapid quenching from 900 °C, is identified to be cubic Bi₆Te₂O₁₃ with an oxygen-deficient fluorite structure, which is isomorphous with -Bi₂O₃.     

X‐ray absorption spectroscopy at the Ni?K edge in Stackhousia tryonii Bailey hyperaccumulator

Young plants of Stackhousia tryonii Bailey were exposed to 34 mM Ni kg^?1 in the form of NiSO₄· 6H₂O solution and grown under controlled glasshouse conditions for a period of 20 days. Fresh leaf, stem and root samples were analysed in vivo by micro x‐ray absorption spectroscopy (XAS) at the Ni? K edge. Both x‐ray absorption near edge structure and extended x‐ray absorption fine structure spectra were analysed, and the resulting spectra were compared with spectra obtained from nine biologically important Ni‐containing model compounds. The results revealed that the majority of leaf, stem and root Ni in the hyperaccumulator was chelated by citrate. Our results also suggest that in leaves Ni is complexed by phosphate and histidine, and in stems and roots, phytate and histidine. The XAS results provide an important physiological insight into transport, detoxification and storage of Ni in S. tryonii plants. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of metal ion on the water structure studied by the Raman O?H stretching spectrum

Raman spectra in the O H stretching region of aqueous salt solutions were measured and compared, and the effects of metal ions on water structure deduced. The effects of alkali ions, alkaline ions or the first‐row transition metals on water structure were found to be similar. Differences of metal ionic effects on water structure exist among Na⁺, Mg²⁺ and Al³⁺, and between Ca²⁺ and Mn²⁺ and Al³⁺ and Fe³⁺. The factors that influence the metal ionic effects on the water structure are the ionic charge, the outmost electronic structure and ionic size, the ionic charge being the most important. With a five‐component Gaussian deconvolution of the Raman spectra of the aqueous solutions of NaCl, MgCl₂, AlCl₃ and FeCl₃ with concentrations of 0 to ∼1mol/l, the ionic effects were found to be similar on the bands at 3233, 3393, 3511 and 3628 cm⁻¹, but different on the band at 3051 cm⁻¹. With increasing polarization of the metal ion, the band at 3051 cm⁻¹, due to strong hydrogen bonding, increases. Copyright © 2009 John Wiley & Sons, Ltd.     

Self‐trapped N?H vibrational states in the polymorphs of glycine,L‐ and DL‐alanine

The polarized Raman spectra of the oriented single crystals of L ‐ and DL ‐alanine, α‐, β‐ and γ‐polymorphs of glycine have been studied at 3–300 K. Regularly spaced band packets have been observed in the spectral range of 2500–3000 cm⁻¹, with intensity decreasing noticeably on heating. These band packets were interpreted as the manifestations of the existence of N H self‐trapped states in these systems at low temperatures. The analysis of the polarized spectra has shown that the self‐trapping is observed exclusively for the NH stretching vibration of the amino groups, which is related to the NH···O hydrogen bonds along the head‐to‐tail chains of zwitterions in the crystal structures. The wavenumber of this NH stretching vibration, however, was proposed to depend not solely on the length of this NH···O hydrogen bond, but also on the lengths of all the other NH···O hydrogen bonds formed by the NH₃⁺ and the COO⁻ groups in the structure linking the head‐to‐tail chains with each other. The arguments in favor of the hypothesis that the self‐trapping in these systems can be mediated by zero‐point quantum motions, and not by lattice phonons, are considered. The unusually low wavenumber (2500 cm⁻¹) observed for the NH stretching vibration and indicating at the formation of a very strong NH···O bond is interpreted based on considering the effect of the crystalline environment on the formation and properties of the NH···O bonds in the head‐to‐tail chains of amino acid zwitterions. The results are interesting for understanding the factors determining the dynamics and structural instability of crystalline amino acids and also for biophysical chemistry, as the hydrogen bonded chains formed by amino acid zwitterions in the crystals can mimic the peptide chains. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal analysis and infrared study of Nb2O5–TeO2 glasses

Tellurite glasses of the xNb₂O₅–(100–x) TeO₂, (3 ≤ x ≤ 20 mol%) system have been prepared and studied by IR spectroscopy and differential thermal analysis to explore the role of Nb₂O₅ on their structure. IR analysis indicates that NbO₆ transforms TeO₄ units into tellurite structural TeO₃ units, with a shift of lattice vibrations towards higher wavenumbers. The stretching force constant of the tellurite structural units increases with Nb₂O₅ content, a feature that is attributed to the higher bond strength and higher coordination number of Nb₂O₅ relative to TeO₂. The crystallization kinetics has been studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results are analyzed, and both the activation energy of the crystallization process and the crystallization mechanism are characterized. The thermal stability of these glasses are characterized in terms of characteristic temperatures, such as the glass-transition temperature, T _g, the temperature of onset of crystallization, T _in, the temperature corresponding to the maximum crystallization rate, T _p, and two kinetic parameters, K(T _g) and K(T _p). The results reveal that thermal stability increases with increasing Nb₂O₅ content. XRD diffraction of the studied glasses indicates the presence of microcrystallites of α-tellurite, γ-telluride, Nb₂Te₄O₁₃ and an amorphous matrix.     

Upconversion Properties of Er3+/Yb3+ Co-doped TeO2–TiO2–K2O Glasses

The Er³⁺/Yb³⁺ co-doped TeO₂–TiO₂–K₂O glasses were prepared by conventional melting procedures, and their upconversion spectra were performed. The dependence of luminescence intensity on the ratio of Yb³⁺/Er³⁺ was studied, and the relationship between green upconversion luminescence intensity and Er³⁺ concentration is discussed in detail. The 546 nm green upconversion luminescence intensity is optimised in the studied glasses either when the Yb³⁺/Er³⁺ ratio is 25/1 and Er³⁺ concentration is 0.1 mol%, or when the Yb³⁺/Er³⁺ ratio is 10/1 and Er³⁺ concentration is 0.15 mol%. These glasses could be one of the potential candidates for LD pumping microchip solid-state lasers.     

TeO2-Nb2O5-YF3 玻璃系统的形成区及性质研究

制备了一种新型的氧卤碲酸盐玻璃:TeO2-Nb2O5-YF3,给出并研究了TeO2-Nb2O5-YF3三元系统的玻璃形成范围。测试了玻璃的密度、折射率、差热(DTA)、拉曼光谱、红外透射光谱以及紫外吸收光谱,通过光谱分析研究了组分含量的变化对玻璃结构及红外透射特性的影响。实验结果表明,TeO2-Nb2O5-YF3玻璃系统具有优良的成玻璃性能和热稳定性等特性,而且在2.8~3.3μm区域内无明显的[OH]基团吸收,在中红外3~5μm区域具有优良透射性能,因此在中红外透射方面具有潜在应用价值。     

Birkhoff’s Polytope and Unistochastic Matrices,N = 3 and N = 4

The set of bistochastic or doubly stochastic N×N matrices is a convex set called Birkhoff’s polytope, which we describe in some detail. Our problem is to characterize the set of unistochastic matrices as a subset of Birkhoff’s polytope. For N=3 we present fairly complete results. For N=4 partial results are obtained. An interesting difference between the two cases is that there is a ball of unistochastic matrices around the van der Waerden matrix for N=3, while this is not the case for N=4.