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- ItemFormation of radiation defects in high-purity silicate glasses in dependence on dopants and UV radiation sources(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Natura, Ute; Ehrt, Doris; Naumann, KarinThe radiation-resistance of high-purity glasses (≈1 ppm iron) of the type BK7®, DURAN® and lead silicate (PbS) with high transmission in the UV region was studied. The investigations were concentrated on the influence of UV-absorbing dopants on defect generation. These were refming agents, AS2O3, Sb2O3, NaCl, and TiO2 as solarization suppressing agent for the visible range in BK7, and small impurities of tin ions in DURAN. The samples were irradiated with UV lamps and excimer lasers (XeCl-308 nm, KrF-248 nm, ArF-193 nm). The defect generation increases with the use of refining agents in BK7 and with the presence of small amounts of Sn2+ in DURAN. The influence of TiO2 on the defect generation strongly depends on the radiation source. Α model explaining the defect generation in these glasses is suggested.
- 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.
- 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.
- 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.
- ItemIrradiation-induced defects in different glasses demonstrated on a metaphosphate glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Möncke, Doris; Ehrt, DorisThe influence of the two polyvalent ions, cobalt and nickel, on the formation of irradiation-induced defects was studied in several different model glasses (silicate, borosilicate, fluoride- and phosphate glasses). In this article the defects are demonstrated on the example of the (SrPO3)2-metaphosphate glass P100. Sample plates of high-purity glasses, undoped and doped with 0.3 mol% CoO and NiO, were irradiated with a UV lamp and with X-rays. The subsequent defect centers, formed at ppm levels, were characterized by EPR as well as optical UV-VIS spectroscopy. Defect recovery experiments were also studied in these glasses. The newly found optical bands and EPR signals evolving in the irradiated glass are in part characteristic for intrinsic defects. These are different types of electron centers (EC) and hole centers (HC) connected with phosphate groups. Other signals arise from extrinsic defects, which are caused by the two dopant ions. The predominant extrinsic defect stems from the photooxidation of Co2+ to (Co2+)2. As an HC the latter replaces some of the intrinsie phosphate-bonded HC and dominates the optical spectra with two bands at 300 and 400 nm. In the glass P100 lamp irradiation photoionizes only Co2+ but not Ni2+. Α new optical band at 330 nm, as well as a new EPR signal at g = 2.08 can be seen only after X-ray irradiadon. Both can be attributed to a nickel-related EC created via the photoreduction of Ni2+ to (Ni2+)-. At the same time the band of the intrinsic oxygen-related HC is intensified. Generally X-ray irradiation causes stronger irradiation-induced defects (excitation of inner electrons) than UV-lamp irradiation (selective excitation of valence electrons).
- 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.
- 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.
- ItemRadiation-induced defects in CoO- and NiO-doped fluoridephosphate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Möncke, Doris; Ehrt, DorisIrradiation-induced defect formation is a common phenomenon in glasses. The influence of the two polyvalent ions cobalt and nickel was studied in several model glasses, two of those were fluoride-phosphate glasses. These studies were done in order to contribute to the ongoing research on solarization. Dopants and impurities may influence the intensity of intrinsic defects and may cause the evolution of additional extrinsic defects. Sample plates of high-purity glasses, undoped and doped with CoO and NiO, were irradiated by UV lamps and X-rays. The formed defect centers displayed absorption bands in the UV-VIS range, which were recorded by absorption spectroscopy. As many defect centers are paramagnetic, EPR spectra of the irradiated samples were taken. The newly found optical bands and EPR signals evolving in the irradiated glasses are in part characteristic of intrinsic defects, which are different types of electron and hole centers connected with phosphate groups. The other signals arise from extrinsic defects, which are caused by the two dopant ions. Co2+ is photooxidized to (Co2+)+, and replaces some of the intrinsic hole centers (POHC), while Ni2+ is photoreduced to (Ni2+)-.
- 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.