Thermal properties of fluoride glasses and their gel precursors

Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.This revised version was published online in November 2005 with corrections to the Cover Date.     

钐对锰激活的硼硅锌存储玻璃的影响

使用高温固相法合成了钐锰共激活的硼硅锌玻璃. 利用热释光谱研究了钐的掺入对锰激活的硼硅锌玻璃的陷阱能级的影响, 发现钐的掺入使后者的缺陷向浅能级方向移动, 表现为锰激活的硼硅锌玻璃的余辉和存储性能的相应变化.     

MEASUREMENTS OF CHAIN INTERPENETRATION OF POLYMER GLASSES

The concept of entanglement provides the basis of our current understanding of the flow behavior of polymer melts, Current techniques developed to investigate the degree of interpenetration of polymer chains only provide indirectly the information of the degree of entanglement in a relatively large scale （several to tens of nanometer）. In this article, we report ^1H-NMR spectroscopy with dipolar filters under fast magic angle spinning for probing chain interpenetration of polymer glasses at the molecular level.     

Charge transfer complexes and salts of ionenes

A review of the synthesis and properties of ionenes is presented. Particular attention is paid to the electrical and related properties of conductive teteracyano-p-quinodimethane (TCNQ) complex salts of ionenes containing ammonium or sulfonium groups in the main chain and to their chemical stability. The recent work on preparation of such ionenes with inorganic and organic counterions which show interesting linear and nonlinear optical properties is also discussed. It is shown that in the solid state ionenes act as a kind of a matrix fixing, in a chemically controlled way, positions and distribution of different kinds of counterions. Because the reaction of counterion exchange is easy in the case of ionenes it provides a convenient way to prepare a broad class of polyelectrolytes with many different properties.     

IR-spectral investigation of the structure of glasses in the Fe2O3-V2O5 system

The structure of glasses in the Fe₂O₃-V₂O₅ system in the 0–50 mol% Fe₂O₃ range is studied by IR-spectroscopy. It is found that the introduction of Fe₂O₃ favours the transformation of the VO₅-groups into VO₄ ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm^–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO₅-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO₄-tetrahedra.

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IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe₂O₃-V₂O₅

Zusammenfassung Die Struktur von Gläsern des Systems Fe₂O₃-V₂O₅ in dem Bereich von 0–50 Molprozent Fe₂O₃ wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe₂O₃ begünstigt die Umwandlung der VO₅- in VO₄-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm^–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO₅-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO₄-Tetraeder zurückgeführt.

     

Hydrogen-Related Paramagnetic Centers in Ge-Doped Sol-Gel Silica Induced by γ-Ray Irradiation

We have studied the generation mechanisms of H(II) paramagnetic centers in Ge-doped silica by investigating up to 10⁴ mol ppm sol-gel Ge-doped silica materials. We have considered materials with the same concentrations of Ge but that are produced by two different densification routes that give rise to different concentrations of Ge-related oxygen deficient centers (GeODC(II)). These centers are characterized by an optical absorption band at ∼5.2 eV (B_2β band) and two related emissions at ∼3.2 eV and ∼4.3 eV. The GeODC(II) content was estimated by absorption and emission measurements. The H(II) centers were induced by room temperature γ-ray irradiation and their concentration was determined by electron paramagnetic resonance measurements. The comparison between the two kinds of materials, obtained by different preparations, shows that the GeODC(II) concentration increases with the Ge content and is enhanced by vacuum densification. The comparison of irradiated samples shows that beyond the already known process of conversion of preexisting GeODC(II) into H(II) centers, another generation process of H(II) centers is effective that involves irradiation induced GeODC(II).     

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2O‐(30–x)K2O‐70B2O3 (5 ≤ x ≤ 25 mol%) glasses

The local distortions and electron paramagnetic resonance parameters for Cu²⁺ in the mixed alkali borate glasses xNa₂O‐(30–x)K₂O‐70B₂O₃ (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na₂O compositions x. Owing to the Jahn–Teller effect, the octahedral [CuO₆]¹⁰⁻ clusters show significant tetragonal elongation ratios p ~19% along the C₄ axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi‐linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi‐linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi‐linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal‐fields and the electronic cloud distribution around Cu²⁺ with the variation of the composition of Na₂O.     

An investigation on visible luminescence of Ho activated LBTAF glasses

Different concentrations of Ho³⁺-doped lead borate titanate aluminum fluoride (LBTAFHo) glasses with chemical composition of PbO-H₃BO₃-TiO₂-AlF₃-Ho₂O₃ were prepared by the melt quenching method. The spectral properties were investigated using the absorption, emission and decay measurements. The experimental oscillator strengths were calculated from the area under the absorption bands. Applying Judd-Ofelt theory, the intensity parameters (Ω_{λ=2, 4, 6}) were calculated, by the least square fit approach from which the radiative transition rates, luminescence branching ratios and radiative decay times were determined. The photoluminescence spectra revealed the quenching of luminescence intensity beyond 1.0 mol% of Ho³⁺ ion concentration. To investigate the luminescence potentiality of ⁵F₄→⁵I₈ emission level, the effective bandwidth and the stimulated emission cross-section were determined. The quenching in experimental decay time is attributed to the resonance energy transfer among the excited Ho³⁺ ions.     

Spectroscopic Investigation of Tungsten Ions in Lead Scandium Phosphate Glass System

Lead scandium phosphate glasses (PbO-Sc₂O₃-P₂O₅) containing different concentrations of tungsten oxide (WO₃) ranging from 0 to 5 mol% were prepared. A number of studies, viz. differential thermal analysis (DTA), infrared spectra, optical absorption, and electron spin resonance (ESR) spectra, have been carried out. The results of DTA indicated the highest glass forming ability for the glass containing 5 mol% of WO₃. The results of spectroscopic studies have been analyzed in light of different oxidation states of tungsten ions.     

Influence of Carbon Multiple Treatments on the Photoelectrical Properties of Porous Glasses

We have studied the influence of multiple carbon treatments on the properties of silica porous glasses. Each step of each carbon treatment started with filling the voids of porous glass with carbon. During the following anneal carbon interacted with the walls of the voids. It was shown that low dimensional silicon clusters were formed inside the voids as a result of this reaction. In the experiments the photoluminescence spectra and conductivity of carbon-processed specimens were measured. The size-distribution of voids in porous glasses was calculated from absorption—desorption isotherms. An original technique was proposed that allowed to obtain the size-distribution of silicon clusters from the positions of peaks in the photoluminescence spectra. Correlation between the photoluminescence intensity and the sizes of pores was revealed. The observed oscillations in the shapes of the photoluminescence spectra in subsequent cycles of carbon treatment are explained by changes of the number of clusters corresponding to definite peaks in the size distribution spectra.