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- 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.
- ItemRadiation-induced defects in CoO- and NiO-doped fluoride, phosphate, silicate and borosilicate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Möncke, Doris; Ehrt, DorisThe influence of cobalt and nickel on the formation of irradiation-induced defects was studied in fluoride, phosphate, silicate and borosilicate glasses. Sample plates of high-purity glasses, undoped and doped with 0.3 mol% CoO and NiO, respectively, were irradiated with UV lamps and with X-rays. The subsequent defect centers, formed at ppm levels, were characterized by EPR and optical UV-VIS spectroscopy. X-ray irradiation caused stronger solarization (excitation of inner electrons) than UV lamp irradiation (selective excitation of valence electrons). More defects were formed in doped than in undoped glasses, generally stronger for Co2+ - than for Ni2+ -doped glasses and especially strong in glasses of high optical basicity where Co2+ and Ni2+ were tetrahedrally coordinated. Co2+ was photooxidized to (Co2+)+ in all glasses, replacing some of the intrinsic hole centers (HC), with (Co2+)+ in tetrahedral coordination: charge transfer band < 400 nm, and (Co2+)+ in octahedral coordination: two bands between 300 and 450 nm. Ni2+ was photooxidized in the (boro-)silicate glasses, which all had a higher basicity, but was photoreduced in the fluoride-phosphate glasses of low basicity. Photoreduced (Ni2+)- was found in the phosphate glass of medium basicity only after X-ray irradiation. The photoionized nickel species also displayed distinct EPR signals, with (Ni2+)+: several bands from 700 to 200 nm, g=2.10; and (Ni2+)-: 330 nm, g1=2.08 and g2=2.26.
- 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.
- 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.
- ItemΑ multi-method characterization of borosilicate glasses doped with 1 up to 10 mol% of Fe, Ti and Sb(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Schütz, Adelheid; Ehrt, Doris; Dubiel, Manfred; Yang, Xiuchung; Mosel, Bernd; Eckert, HellmutThe model glasses NBS1 and NBS2 are sodium borosilicate glasses of high intrinsic UV transmission. Although both glasses have an SiO2 content of 74 mol%, they possess different matrix structures due to varied Na2O / B2O3 ratios. Nonbridging oxygens occur in the NBS1 but not in the NBS2 glass. Fe, Ti and Sb oxides were added at concentrations of 1 and 10mol% to study valence, coordination and site distribution. XANES, Mössbauer, optical absorption, photoluminescence and EPR spectroscopy provided an insight into the structures and near range environments of the dopants. Large differences were found for the two Fe doped glasses. The presence of nonbridging oxygens in NBS1 glass leads to a higher solubility of the Fe ions and a higher ratio of tetrahedral over octahedral Fe3+ coordination while a clustering of Fe ions resulting in a lowered UV and VIS transmission is observed in NBS2 glass. In Ti doped glasses EPR and XANES spectroscopy shows that most Ti occurs as Ti4+, in four-, five- and sixfold coordination. Optical spectra of Ti4+ display high intensity charge transfer transitions in the UV region. Ti4+ photoluminescence in the visible range is of low intensity. Optical absorption, XANES and Mössbauer spectroscopy could only detect Sb3+ in the antimony doped glasses. The photoluminescence of Sb3+ is much stronger in the NBS1 than in the NBS2 glass.
- 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.
- 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.
- 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.
- ItemInfluence of melting and annealing conditions on the optical spectra of a borosilicate glass doped with CoO and NiO(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Möncke, Doris; Ehrt, DorisIn the high-viscosity borosilicate glass (NBS2) doped with 0.3 mol% CoO or NiO quenching resulted in a freeze-in snap-shot of the glass structure within the dopants' transformation process from their high-temperature tetrahedral coordination to the octahedral form normally present in this glass at room temperature. In this transitional state the octahedral, tetrahedral and a third pseudotetrahedral transitional coordination are simultaneously present. The optical spectra of the doped glasses are discussed in relation to the different melting and cooling conditions applied. Quenched glasses were also tempered on a heating table, which permitted to take the optical spectra at each temperature step. In contrast to Co2+, Ni2+ has a strong octahedral preference. Thus for NiO-doped NBS2 glass tempering or annealing always results in relaxation into the octahedral coordination. For Co2+, which is also octahedrally coordinated in the annealed NBS2, tempering of the quenched glass leads to a relaxation into octahedrally and tetrahedrally coordinated Co2+. These structural changes are especially strong when the applied temperatures lie 150 to 200 °C above Tg of the NBS2 glass where also the viscosity-temperature curve implies structural changes within the glass matrix.