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- 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.
- 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.
- 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 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.
- 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.
- 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.
- 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).