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- ItemInfluence of modifier cations on the radiation-induced effects of metaphosphate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Ebeling, Polina; Ehrt, Doris; Friedrich, ManfredThe influence of different modifying cations on the radiation-induced defect generation in metaphosphate glasses was studied by optical absorption and electron paramagnetic resonance spectroscopy. For this task, several model glasses were prepared. These were simple metaphosphates of alkaline earths, aluminum and zinc. The synthesized glass samples were irradiated with X-rays and with UV light from an Xe/Hg lamp. The cation-dependent differences in the structure of the phosphate glasses were found to have a great influence on the concentration of some radiation-induced defects and thus on the optical absorption. The influence of the different cations became especially distinct under UV light Irradiation due to the selective interaction of the UV light with the glass samples. Some additional phenomena were observed for the irradiated zinc and magnesium metaphosphate glasses which were not found by the previously undertaken study of complex phosphate glasses.
- ItemEstimation of deep-uv and uv absorption coefficients of selected trace impurities in glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Seeber, Wolfgang; Ehrt, DorisGlasses of the fluoride phosphate type were selected as suitable host materials for studying the uv absorption behavior of several transidon metal ions in different valence states (Fe²⁺/³⁺, Cu⁺/²⁺, Pb²⁺, Ni²⁺, Cr³⁺). Based on a large glass sample collecdon with series of transition metal-ion-doped fluoride phosphate glasses together with a carefully analytically determined real impurity content, the specific uv absorption spectra of the mentioned ions could be estimated using nonlinear deconvolution of bands.
- ItemCarbon crucible technology for optical glass melting(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Müller, Michael; Carl, Matthias; Kittel, Thomas; Ehrt, DorisFluoro crown and phosphate crown glasses are attractive candidates for application in the deep ultraviolet range. The calculated values for the ultraviolet resonance wavelenghts are comparable with those of CaF₂, BeF₂ and SiO₂. However, the experimental ultraviolet transmission of glass is frequently limited by extrinsic absorption due to trace impurities of metal ions, mainly iron, copper and lead. The influence of different technological parameters on the ultraviolet transmission and the glass quality was investigated, especially the effect of reducing melting conditions, by using a carbon crucible in a glove box. The ultraviolet absorption of the glass is strongly dependent on the redox conditions of the melt, the reducing temperature and time. Glasses melted under reducing conditions have a much higher transmission at 250 nm due to the shift of redox equilibria of polyvalent transition metal ions to the lower redox state and the fact that the molar absorption coefficients of the lower redox states are more than one order of magnitude lower than those of the higher redox state in the ultraviolet range. Undesirable side reactions that may occur under strong reducing melting conditions are described. Using carbon crucible technology for fluoro and phosphate crown glass melting it is possible to achieve high UV transmission values and a good inner glass quaUty.
- ItemTime resolved fluorescence measurements on Tb3+ and Mn2+ doped glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Herrmann, Andreas; Ehrt, DorisTb3+ (4f8) and Mn2+ (3d5) ions, known as active luminescent centres for blue, green and red fluorescence, were doped in various fluoride, phosphate and Silicate glasses with well known structure. Narrow bands of f-f transitions with strong emission of Tb3+ in the blue, green and red and broad bands of d-d transitions of Mn2+ were measured with green emission in high optical basicity glasses with tetrahedrally coordinated Mn2+. Orange to red Mn2+ emission was found in glasses with low optical basicity where Mn2+ is octahedrally coordinated. Lifetimes, τe, in the range of milliseconds were recorded in dependence of glass composition and dopant concentration for both Tb3+ and Mn2+ doped glasses. Fluorescence lifetimes are as well shortened by higher basicity of the glasses as by increasing dopant concentration.
- ItemFormation of radiation defects in Silicate and borosilicate glasses caused by UV lamp and excimer laser Irradiation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Natura, Ute; Ehrt, DorisSolarization of colourless and coloured glasses of the type AR®, BK7® and DURAN® with high transmission in the UV-B region (280 to 320 nm) was investigated for their use as Container glasses in the solar disinfection of drinking water. The samples were coloured by doping with NiO or CoO. The influence of the Fe³⁺/Fe²⁺ content and of the reducing component Sn²⁺ was investigated on both the initial transmission of the glasses and the solarizadon. The samples were irradiated with a 1 kW Xe lamp and a XeCl excimer laser. The solarization depends on the glass matrix and is enhanced by colouring ions. The influence of Fe³⁺/Fe²⁺ and Sn²⁺ on the defect generation is different for glasses coloured with NiO than for those coloured with CoO. For the samples investigated it was possible to simulate the loss of transmission in the UV-B region due to long-time irradiation with sunlight by a laser experiment.
- ItemVoltammetric investigations of the redox behaviour of Fe, Ni, Co and Sn doped glass melts of AR® and BK7® type(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Matthai, Annegret; Ehrt, Doris; Rüssel, ChristianThe redox behaviour of iron, nickel, cobah, and tin ions was studied in glass melts with compositions near AR® and BK7® type by means of square-wave voltammetry (SWV). From the linear dependence of the peak potentials on the temperature, the standard enthalpies, ΔH°, and the standard entropies, ΔS° of the transitions Fe3+/Fe2+, Co2+/Co0, Ni2+/Ni0, Sn4+/Sn2+ and Sn2+/Sn0 were calculated. The reduced states are formed in the AR glass melt already at less reducing conditions than in the BK7 melt. The dependence of the redox ratios upon temperature is larger in the AR melt. As colouring ion Co2+ is more advantageous than Ni2+ because of its higher stability against reduction. It is possible to reduce the Fe3+/Fe2+ ratio without formation of Co0 in a disturbing concentration.
- ItemThermodynamics of redox equilibria and diffusion of polyvalent ions in a phosphate glass melt(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Matthai, Annegret; Claußen, Olaf; Ehrt, Doris; Rüssel, ChristianΑ phosphate glass melt with the basie composition of NaPO₃ · 2Sr(PO₃)₂ doped with various oxides of polyvalent elements (Fe₂O₃, AS₂O₃, Sb₂O₃, CuO and SO₄²¯) was studied with the aid of Square-wave voltammetry. The Standard potentials depended linearly on temperature. The Standard enthalpy ΔH⁰ and the Standard entropy ΔS⁰ of the attributed redox reactions were calculated from the Standard potentials measured. The diffusion coefficients were determined from current densities obtained and fulfilled the Arrhenius' law. Both thermodynamics of the redox equilibria and diffusion coefficients are compared with those measured in soda-lime-silica glasses.
- ItemRedox behavior of iron and vanadium ions in Silicate melts at temperatures up to 2000 °C(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Leister, Michael; Ehrt, DorisTwo glasses 33Na₂O · 67SiO₂ and 15Na₂O · 85SiO₂ (composition in mol%), doped with Fe₂O₃ and V₂O₅, respectively, were melted under various conditions in the temperature ränge of 1400 to 2000 °C. The redox states in the quenched glasses were investigated by optical absorption spectroscopy. Investigations concerning the redox equilibrium of the polyvalent ions in the glass melts were carried out using square-wave voltammetry. The results of both methods were compared. Furthermore equilibrium experiments were carried out to show the time dependence of redox equilibrium reached.
- ItemDetermination of the OH content of glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Ebendorff-Heidepriem, Heike; Ehrt, DorisThe most widely used method for determination of the OH content of glasses is the IR spectroscopy. The absorption bands in the range of 2500 to 4000 cm⁻¹ are due to the fundamental stretching vibrations of OH groups having different degrees of association. The calibration of the absorption coefficient, α, of an OH band requires the determination of the absolute OH content of some samples by another method than IR spectroscopy. Comparing water outgassing method with ¹H NMR spectroscopy, a large difference in the OH content was observed. Therefore, it is more appropriate to use solely the absorption coefficient as a relative measure of the true OH content. If certain requirements are met, the quantitative analysis of the absorption coefficient of different glass samples is justified.
- ItemStudy of radiation-induced defects in fluoride-phosphate glasses by means of optical absorption and EPR spectroscopy(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Ebeling, Polina; Ehrt, Doris; Friedrich, ManfredFor the X-ray irradiated fluoride-phosphate (EP) glasses with different phosphate eontent (from 0 to 20 mol%), a number of different radiation-induced defect centers (DC) were detected, which can be subdivided into three groups: phosphate, oxygen and fluorine related DC. The phosphate and oxygen related defects are paramagnetic, their optical absorptions were established by means of band separation and correlation to EPR signals. The non-paramagnetic fluorine-related color centers (FD centers) were found for FP glasses with lower (≤ 2 mol%) phosphate content by means of band separation of induced spectra of optical absorption and annealing experiments.