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- 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.
- 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.
- 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.
- 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.
- 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.
- ItemOptical spectroscopy of rare earth ions in glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Ebendorff-Heidepriem, Heike; Ehrt, DorisThe relationships between host glass composition and optical properties of rare earth ions were studied by means of absorption and emission spectroscopy. Eu³⁺ and Tb³⁺ were found to be appropriate indicator ions for determining the properties of the local environment around rare earth ions. Er³⁺ and Nd³⁺ ions are widely used in lasers and amplifiers. The knowledge of the compositional influence on the spectroscopic parameters of rare earth ions enabled the modeling of the emission properties of important Er³⁺ and Nd³⁺ transitions in order to figure out the Optimum host glasses. Fluoride phosphate and phosphate glasses are attractive candidates for lasers and amplifiers. In these glasses, the degree of covalency between the rare earth ions and surrounding ligands mainly affects the spectroscopic parameters of rare earth ions such as Judd-Ofelt parameters and electron-phonon coupling strength. The increase of the electron-phonon coupling strength with the phosphate content is responsible for the decrease of the Er³⁺ emission intensity at 540 nm. Otherwise, it increases the Er³⁺ emission intensity at 1.5 µm in the fluoride phosphate glasses. The lower microparameters of Nd³⁺ cross relaxation in phosphate glasses cause the higher lifetimes of the Nd³⁺ ⁴F₃/₂ laser State at higher Nd³⁺ concentrations with respect to fluoride phosphate glasses. The energy transfer to OH groups in phosphate glasses decreases the hfetime and emission intensity of the laser State of both Er³⁺ and Nd³⁺ ions.
- 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.