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- 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.
- 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.
- 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.
- 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 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.
- ItemUV light induced photoreduction in phosphate and fluoridephosphate glasses doped with Ni2+, Ta5+, Pb2+, and Ag+ compounds(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Möncke, Doris; Ehrt, DorisThe photoreduction of polyvalent ions was studied in high purity fluoride-phosphate and metaphosphate glasses doped with Ni2+ (3d8), Ta5+ (5d0), Pb2+ (6d2), and Ag+ (3d10). Compared to the undoped base glasses all doped samples display different electronic transitions in the UV at the irradiation wavelength. Glass samples containing 50 to 5000 ppm dopants were irradiated with excimer lasers at 193 and 248 nm, respectively. The subsequent defect centers, formed at ppm levels, were characterized by EPR and optical UV-VIS spectroscopy. The observed laser induced transmission losses in the UV and visible range increased in the order Ni, Ta, Pb to Ag. Extrinsic electron centers are formed by photoreduction of the dopants. (Ni2+)- is characterized by an optical transition with a maximum at 355 nm and an EPR signal around g ≈ 2.07. The maxima of the optical transitions of the (Pb2+)- -EC are positioned at 395 and 500 nm, of the (Ta5+)- -EC at 465 nm. The photoionization products of silver depend strongly on the silver concentration. At a silver content of 50 ppm only the (Ag+)- -EC is formed, visible in the optical spectra with a maximum around 450 nm. Α second silver species, (Ag+)2 -, which absorbs at 305 nm, is additionally observed in the sample doped with a silver concentration of 500 ppm. In the sample doped with 5000 ppm silver a third defect, the photooxidized (Ag+)+ -HC, with an optical band maximum at 405 nm and an EPR signal around g ≈ 2.3 is observed as well. The formation of extrinsic electron centers causes in all glasses an increase in the formation of intrinsic hole centers and often a decrease in the formation of intrinsic electron centers. Defect generation curves show that a very rapid darkening in the glasses is initiated by the addition of any of these dopants. The recovery rates of the defeets formed depend strongly on the dopant, not on the glass matrix.
- 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).