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Phosphate glasses are of great interest for basic research and for special applications in various fields as technical and optical glasses. Metaphosphate compositions with PO4-chain structure are mostly used. The cations have a significant effect on the properties of the glasses and melts. This was studied in more details. High purity metaphosphate glasses, Mn(PO3)n with M = Na+, K+, Zn2+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+ and Fe3+, were prepared and the optical and thermal properties were measured with different methods. The electrical conductivity of glasses and melts is the property of great practical importance. It was determined by impedance spectroscopy in a wide temperature range from 300 to 1250 °C in frequency range of 0.1 Hz to 6 MHz. The electrical conductivity of alkaline earth phosphate glasses and melts increases with increasing ion radius of the cation. NaPO3 and KPO3 glasses and melts have much higher conductivity. Viscosity measurements were carried out from transformation temperature, Tg, to the melt. The measured data were fitted and the activation energies of the conductivity and viscosity were calculated. Simple exponential behavior was found at temperatures below Tg, but above Tg only in very narrow temperature range. The relation between conductivity and viscosity was considered.

Materials with high deep-ultraviolet (DUV; λ2, fluoride, phosphate, multicomponent silicates, and organic materials (PMMA), were investigated. The role of intrinsic absorption (UV edge) due to electron transitions between the main components, and extrinsic absorption due to trace impurities, effect of polyvalent ions, redox behavior, and radiation-induced transmission loss were considered. The optical basicity and optical properties were used to order the materials.

The local structure of the model glasses (NaPO3)1–x-(AlF3)x (0 ≤ x ≤ 0.4), prepared by standard melt-cooling, was extensively investigated by high-resolution solid-state nuclear magnetic resonance (NMR) including advanced double-resonance techniques. This glass system offers the opportunity of studying five different heteronuclear distance correlations (Na–F, Na–P, P–F, Al–F, and P–Al) by 10 distinct double-resonance experiments, involving all of the constituent elements present. 27Al MAS-NMR data indicate that aluminum is predominantly six-coordinated. According to 27Al{31P} and 27Al{19F} rotational-echo double-resonance (REDOR) spectroscopic results, two to three Al–F and three to four Al–O–P linkages occur in these glasses, independent of composition x. 19F MAS-NMR spectra show the presence of terminal P-bound and Al-bound fluorine species. A small amount of fluorine bridging to two aluminum octahedra, which could be assigned based on 19F{27Al} and 19F{31P} REDOR experiments, was also detected. 19F{23N...

International audience; In an earlier review we discussed the connectivity in borosilicate glasses and compared our experimental findings by NMR, infrared and Raman spectroscopies with older structural models. We could show, contrary to the often cited reedmergnerite type model, that a significant preference exists in low alkali borosilicate glasses for trigonal rather than tetrahedral borate groups to link to silicate entities. Another often cited misconception is the application of the Loewenstein rule to borate tetrahedra. While linking of two "[AlØ4]– tetrahedra is disadvantageous compared to higher coordinated aluminate polyhedra, the borate tetrahedral units represents already the alternate higher coordination state and accordingly, many examples of linked [BØ4]– tetrahedra are known to exist in glasses as well as in crystalline compounds of boron at normal pressure conditions. We now present more NMR data on three different low alkali borosilicate glasses with Na2O:B2O3=0·2 to 0·35 and decreasing SiO2 fractions (74 to 43 mol% SiO2), for which we compare variations in the near and intermediate range structure of quenched and slowly annealed samples. None of the studied glasses showed a significantly higher fraction of trigonal BØ3 groups in the quenched than in the annealed samples, even though borate in the three-coordinated state is the preferred metaborate unit in the melt. However, for the two silicate rich glasses (including NBS 2), we observe at low temperatures a deviation of the viscosity–temperature plot from the ideal VFT-fit, that is from Tg at circa 440 to the expected 600°C. For samples prepared at any annealing temperature below 600°C, structural variations with thermal history are apparent, and are also reflected in many glass properties including density, fracture probability, or refractive index. Even though the glass NBS 2 shows no visible phase separation, DSC measurements indicate the presence of two different Tg values corresponding to the borate and the silica rich subnetworks. The values of the two Tg events shift with different cooling rates: for fast quenched glasses the two Tg values are closer together than for slowly annealed glasses. The study of these low alkali borosilicate glasses is ongoing, as we understand better how structural variations with changing thermal history impact the glasses' properties. Analogously, we can apply the same techniques to follow structural variations under external forces, such as irradiation, laser modification, pressure and mechanical impact.

Electron paramagnetic resonance (EPR) and fluorescence spectroscopy are sensitive and selective methods for probing coordination and bonding of Mn2+ ions in glasses. Both methods provide additional information on Mn–Mn ion interactions and cluster formation. Mn2+ was found to be tetrahedrally coordinated in boro-silicate glasses of high optical basicity, and octahedrally coordinated in low alkaline boro-silicate glasses (duran-type) as in fluoride-phosphate glasses. Broad emission bands and multicomponent fluorescence decay curves in duran glasses indicate very strong Mn–Mn ion interactions and the presence of multiple Mn2+ sites. Site distribution is more homogenous in metaphosphate glasses, though concentration quenching is apparent at high Mn-levels. As the Mn-content increases the EPR spectra show exchange narrowing due to a decrease in the Mn–Mn distances in the duran series, but show extreme linewidth broadening due to increased cluster sizes at constant Mn–Mn distances for metaphosphate glasses. For the fluoride-phosphate and boro-silicate systems investigated, fluorescence lifetimes are found to decrease as the wavelength of the emission maximum increases and with increasing g-values of the sextet at g = 2. For octahedral coordination of Mn2+ ions the EPR hyperfine splitting constant decreases linearly with increasing optical basicity, as a result of an increasing covalent character of the Mn2+–ligand bond.

We present a plasma mirror configuration that improves the temporal pulse contrast of femtosecond terawatt laser pulses by a factor of thousand using a single antireflection coated glass target. The device provides ultra-high contrast for experiments with a maximum repetition rate of 10 Hz. A third-order cross-correlator has been used to measure the temporal pulse contrast for several different plasma mirror targets. It is shown that the ASE can be suppressed to a level of 10−11. A comparison between a triggered and an untriggered plasma mirror reveals differences in the intensity distribution of the focused beam. The triggered plasma mirror produces a slightly larger focus due to the expansion of the triggered plasma mirror at −3 ps before the main pulse. We propose a cost-effective AR-coated and a blank glass target to reduce the costs of the consumable target material. High-harmonic radiation on solid surfaces has been generated with different plasma mirror targets to demonstrate the high laser contrast.

Structural, optical, and physical properties of glasses prepared by melt reduction in the mixed Sr−Mn metaphosphate system xMnO−(1 − x)SrO−P2O5, 0 ≤ x ≤ 1, have been investigated by vibrational, optical, EPR, and thermal techniques. Mn ions were found mostly in the +2 oxidation state and in sites of octahedral symmetry. Such sites are formed by neighboring Mn−oxygen polyhedra, where the covalent character of Mn−O bonding increases with cation mixing. The phosphate structure was found to consist predominantly of metaphosphate tetrahedral species (Q2) with a minority of pyrophosphate (Q1) and neutral (Q3) phosphate tetrahedra, whose relative abundance changes nonlinearly with MnO content. The symmetric stretching vibration of terminal PO2− units in Q2 species was employed to probe the influence of mixed Sr/Mn environments on phosphate structure, and the results suggested a deviation from the homogeneous distribution of metal cations. This was attributed to the coordination numbers of Sr and Mn ions (i.e., 8...

Various fluoride, phosphate and borosilicate glasses with known properties and global structure have been doped with Eu3+ (4f6) at doping concentrations between 1018 and 1021 cm−3. By applying reductive melting conditions Eu3+ could partially be transformed to Eu2+ (4f7). Four fluoroaluminate glasses with varying phosphate content between 0 and 20 mol% (FPx), a pure phosphate glass (P100) and two borosilicate glasses with low (DURAN®-like) and high optical basicity (NBS1) have been used for these investigations. The time-resolved fluorescence in the visible range has been studied for both ions. Although static and dynamic fluorescence of Eu3+ and Eu2+ are dramatically different (f–f-transitions for Eu3+; d–f-transitions for Eu2+), glass structure changes have a similar influence on the dynamic fluorescence behavior of both ions. A strongly ionic surrounding due to fluorine ligands as in fluoroaluminate glass samples provides the longest fluorescence lifetime (about 7 ms for Eu3+; about 1.3 μs for Eu2+). Increasing phosphate content decreases the fluorescence lifetime due to more oxygen ligands. Interesting differences have been found for the two borosilicate glasses due to the difference in their optical basicity (Na2O/B2O3 ratio). Measurements indicate a homogeneous distribution of europium ions in most FP samples. NBS1 measurements suggest that two different local europium sites are formed. For Duran-like samples only one specific europium site was found, although these samples show phase separation at high doping concentrations into a SiO2-rich phase and borate- and europium-rich droplets. Fluorescence quenching due to energy transfer from Eu2+ to Eu3+ could be found for co-doped samples; Eu3+-doped samples show no fluorescence quenching.

Glasses in the composition range in mol% 35-50 ZnO – 10-15 Al2O3 – 40-55 SiO2 were prepared, undoped and doped with 1 x 1019 and 1 x 1020 Sm3+ per cm3 glass as luminescent species for the visible region, especially for blue and red emission. Phase separation occurs in glass samples with high SiO2 content. SiO2-rich droplets in a Zn2+- Al3+- enriched matrix were formed. Sm3+ ions prefer the Zn2+-Al3+-rich glass matrix. By thermal treatment glass samples were transformed into glass ceramics with the main crystal phases: Zn2SiO4 (willemite), ZnAl2O4 (gahnite) and SiO2-mixed crystals. XRD, SEM and TEM measurements were carried out. The luminescent Sm3+ ions are concentrated in the glass matrix. Photoluminescence excitation and emission spectra were recorded in the UV-VIS-region and the time resolved emission behavior was measured by excitation with a N2-laser at 337 nm. The glasses and glass ceramics have interesting chemical and physical properties, high Tg around 700°C, low coefficient of thermal expansion ~ 4 ppm/K, and high chemical stability.

Glasses with 55–60 mol% SnO and 40–45 mol% P2O5 have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low Tg, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher Tg, 250–300 °C, and much higher chemical stability. No significant differences were found by 119Sn Mossbauer and 31P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and 1H Nuclear Magnetic Resonance spectroscopy. In samples with low Tg, a broad O H – vibration band around 3000 nm with an absorption intensity >20 cm−1, bands at 2140 nm with intensity ∼5 cm−1, at 2038 nm with intensity ∼2.7 cm−1, and at 1564 nm with intensity ∼0.4 cm−1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity

The thermal history impact on the short- and medium-range order structure, that is, the connectivity of borate and silicate entities, is studied for the low - alkaliborosilicate glass NBS2 (74SiO2- 20.7B2O3 - 4.3Na2O - 1Al2O3 inmol %) using vibrational 1D and 2D 11B NMR spectroscopic techniques.Both 11B-NMR and vibrational spectroscopy show a slightly higher fraction of trigonal over tetrahedral borate groups in glass samples which are splat quenched from a final melting temperature of 1750°C than that in carefully annealed samples. Regarding the medium-range order structure, a more mixed silicate-borate network reflected by a higher fraction of B–O-Si bonds characterizes the quenched sample, while more homopolar B-O-B and Si-O-Si bonds are found in the annealed sample. The direct analysis of the B-O-Si linkages by 2D 11B/29Si NMR correlation confirms this conclusion. Interestingly, all signals due to interactions between [BØ4]- and silicate units disappear in the annealed samples (Ø denotes bridging oxygen ions), whereas the only remaining signals represent the spatial proximity of three-fold coordinated boron and silicate units in B3-O-Si bonds.

(Fluoride)phosphate and borosilicate glasses of high intrinsic transparency in the deep ultraviolet (UV), were doped with 50–5000 ppm of the 4d- and 5d-ions Zr, Nb, Ta, Mo, or W. All of these ions absorb strongly in the UV. Samples plates were irradiated by UV lasers and the as a consequence generated various extrinsic and intrinsic defects were characterized by optical and EPR spectroscopy. The laser induced transmission changes depend not only on the glass matrix, but also on the valence of the dopants. Only fully oxidized d0-ions are observed in fluoroaluminate glasses. Laser irradiation photoreduces the d0-ions to extrinsic electron-centers (EC). Laser induced transmission changes extend from the UV up to 600 nm in the visible. The dopants are easily reduced to lower valences in metaphosphate glasses. Extrinsic hole centers (HC) replace intrinsic HC in samples containing the reduced transition metal ions. The strong transmission changes seen below 300 nm arise from intrinsic EC and extrinsic HC. The few remaining intrinsic HC (300–600 nm) recombine rapidly with EC or transform into more stable extrinsic HC. Borosilicate glasses show the formation of intrinsic boron oxygen hole center in the EPR spectra and of intrinsic HC and EC in the optical spectra. The d1-ion Mo5+ is the only identified reduced dopant species in the borosilicate glasses. The band intensity of intrinsic EC in relation to intrinsic HC is correspondingly highest for the Mo-doped samples, in which extrinsic HC are generated.

Photoluminescence in the ultraviolet and visible region is a very sensitive analytical method and also an important optical property of glasses which depends strongly on active centers, surrounding host glass composition and their interactions. Fluoride, phosphate, and silicate glasses doped with active luminescent ions of different electronic configurations were investigated. Ions with s 2 configuration, Sn 2+ , Pb 2+ , Sb 3+ , absorb strongly in the ultraviolet and yield broad emission bands in the ultraviolet and blue spectral area. Mn 2+ ions (3d 5 ) provide broad red emission in fluoride and phosphates due to octahedral coordination, and green emission in silicates by tetrahedral coordination, with long lifetime. Rare earth ions with 4f n configuration show a lot of sharp excitation and emission bands. Red emission is given by Sm 3+ (4f 5 ) and Eu 3+ (4f 6 ) ions in all glasses investigated. Yellow emission of Eu 2+ (4f 7 ) was detected in fluorides. Efficient green emission was obtained with Ho 3+ (4f 10 ) and Er 3+ (4f 11 ) especially in fluoride hosts.

The localized modification of the refractive index in different glasses using a femtosecond laser direct-writing technique at 800 nm is described. The induced refractive-index changes were positive and negative depending on glass composition and laser-writing conditions. The optical properties of the generated structures were studied with different methods. Quantitative measurements were possible with a special interference microscope with shearing technique. Large differences were detected depending on glass composition and structure. Selected glasses were fused silica, multi-component borosilicate, borate and fluoride phosphate glasses. The induced refractive change in fluoride phosphate glasses increased with increasing phosphate content up to ∼5 × 10 −3 . A redistribution of fluoride and phosphate groups in the local irradiated volume is assumed in correlation with the crystallization behavior of these glasses.

The POLARIS project aims at the development of an all-diode-pumped, high-peak-power femtosecond laser system reaching the petawatt level. The laser amplifiers are based on pumping Yb3+-doped fluoride phosphate glass at 940 nm. Recently, stable operation of the first three amplifiers was achieved. Pulses with a bandwidth of 12 nm, which supports 135 fs pulses with energies up to 1.25 J, were generated in the third amplifier with a 12-pass configuration. The amplifier was pumped by 150 collimated high-power laser diodes. Successive polarization maintenance is used for a compact, stable, and convenient adjustable setup. Thermally induced abberations of lowest order were compensated by adaptive mirrors.

The extent of solarization is strongly influenced by many factors such as glass matrix, dopants, or irradiation source. Typical irradiation induced effects are illustrated in a series of glasses doped with a selection of polyvalent ions. Intrinsic and extrinsic defects, consisting of electron and hole centers, are characterized with optical and EPR spectroscopy. Used in combination, both spectroscopic methods allow to detect a wide range of defects. UV-lamp irradiation causes in fluoride-phosphate glasses the photoreduction of Ni 2þ ,P b 2þ and Ag þ while Co 2þ ,C e 3þ ,F e 2þ and Mn 2þ are photooxidized. The influence of the glass matrix is evident for Ni 2þ which is photooxidized in borosilicate, but reduced in fluoride-phosphate glasses. Iron ions also show different redox reactions depending on the glass matrix, as well as on the melting conditions, which will be shown for low alkaline borosilicate glasses doped with iron or tin. Changes in the nature and the rate of defect formation could be observed within the irradiation process of a fluoride-phosphate glass co-doped with Mn 2þ and Fe 2þ and during thermal annealing of a lamp irradiated phosphate glass containing Co 2þ . The series Mn 2þ ,F e 2þ ,C o 2þ and Ni 2þ shows a trend of increased photooxidation with increasing electro-negativity or

Designing pulsed laser amplifiers requires detailed knowledge about beam distortions at the amplifying medium. Time resolved experiments have been performed on fluoride phosphate and pure phosphate glass in order to study optical aberrations induced by pump beam irradiation. By means of a probe beam tunable in wavelength, it was possible to discriminate between thermally induced variations of the optical path and beam narrowing effects due to the radial gain distribution. The experimental results were analyzed theoretically regarding Fresnel diffraction. A quite different response was found for the two types of glass despite their similar nominative properties.

Fluoroaluminates are well known glass formers. Although their glass forming ability is low, it can be increased by doping with phosphates. Structure and properties depend mainly on the fluoride to phosphate ratio. In this review a number of recent developments in the use of these glasses for the fabrication of active laser and amplifier materials is discussed.

Intrinsic and extrinsic ultraviolet absorption and radiation-induced effects were investigated in different glass types, fluorides, phosphates and borosilicates. High-purity glass samples were prepared and their intrinsic absorption was measured in the vacuum ultraviolet region. The influence of doped iron and tin species in the ppm range on the ultraviolet absorption and radiation-induced effects were studied. The maximum of the dominating Fe 3+ charge transfer band has the lowest energy (4.8 eV) and intensity in the fluoride glass and the highest energy (5.6 eV) and intensity in the borosilicate glass samples. The charge-transfer band for Fe 2+ has much lower intensity and higher energy (∼5.7 eV) than those for Fe 3+ in all glasses investigated. Photo-oxidation of Fe 2+ to (Fe 2+ ) + hole centres and glass-matrix-related electron centres by UV irradiation increases the UV absorption drastically in all glasses. The kinetics was measured and simulated depending on the glass matrix. In fluoride and phosphate glasses, Fe 3+ complexes are very stable against UV irradiation and do not participate in UV-radiation-induced processes. Only in silicate glasses, Fe 3+ is able to form a (Fe 3+ ) – electron centre defect which decreases the charge transfer absorption of Fe 3+ near 220 nm, but increase the absorption of hole centre defects, with a maximum at 280 nm. So, the defect generation in the ultraviolet region increases drastically with increasing Fe content in the range 10–200 ppm. Three or four electronic s → p transitions for Sn 2+ were detected by optical absorption and luminescence spectroscopy shifted to longer wavelength in the range fluoride → phosphate → silicate glass samples. Sn 4+ absorption bands were found at shorter wavelength in the vacuum ultraviolet region in all cases investigated. Sn 2+ ions are photo-oxidised under UV radiation very fast, which leads to an decrease of absorption near 200 nm and to an increase near 250 nm. Both Sn 2+ and Sn 4+ are involved in the radiation-induced processes. In contrast to phosphate and silicate glasses, tin-doped fluoride glasses are very resistant against UV lamp but not against UV laser irradiation. The mechanisms are very complicated, with maximums and minimums in the defect formation curves.

Optical absorption and paramagnetic resonance spectra of X-ray irradiated (λCuKα=0.154 nm) ultra- and metaphosphate glasses of high purity were studied. Melting of the samples under different redox conditions, investigation of annealing behavior of the irradiated samples and correlation between optical and EPR spectra allowed the resolution of five main paramagnetic radiation-induced defects and associated optical absorption bands. Phosphorus and oxygen related radiation-induced defects were found, with hole centers POHC and OHC absorbing in the visible and electron trapped centers PO2, PO3 and PO4 absorbing in the ultraviolet region.

The energy-transfer rate coefficient from ytterbium to erbium (K) and upconversion rate coefficient for erbium (C) are determined by analysis of erbium fluorescence decay under different pumping conditions. A simple rate-equation model was used to describe the fluorescence dynamics. Numerical analysis of the model delivered K and C as fit parameters to the experimental curves. Values of K ranging from 0.75-1.42 x 10-16 cm3/s and C from 0.8-1.7 x 10-18 cm3/s were found. The results obtained are of the same magnitude as results for phosphate glasses reported in the literature. Further analysis showed that high erbium concentrations (2 x 1020 cm-3 ) need a much higher pump intensity to reach threshold due to increased losses caused by upconversion.

The study of radiation-induced defect formation in glasses is of growing interest for applications in optics and photonics. The influence of Tb3+ ions on X-ray-induced defects has been examined in glasses with different phosphate contents. The defects have been characterized by optical absorption and ESR spectroscopy. (Tb3+)+ ions are formed by X-ray irradiation. They exhibit a broad charge transfer band at 370 nm. The formation of (Tb3+)+ hole centres suppresses the formation of intrinsic phosphate-related hole centres, absorbing in the visible region. PO3 defects absorbing in the ultraviolet region contribute mainly to the electron centres corresponding to the (Tb3+)+ hole centres. Immediately after X-ray irradiation, 5–10% of the Tb3+ ions have been oxidized. The amount of (Tb3+)+ ions increases with increasing phosphate content. The stability of the (Tb3+)+ ions at room temperature depends on glass composition and melting conditions.

High purity fluoride phosphate (FP) glasses have a large transmission range from the vacuum ultraviolet to the infrared. They are attractive candidates for lens systems in microlithography equipment and excimer laser optics. Fluoride single crystals and vitreous silica are well-known traditional materials for ultraviolet optics. Crystal sizes are limited and glass is better for fabricating optics. For lens systems, a variety of glasses with different refractive indices and dispersion are required. The UV resonance wavelengths of FP glasses with a low content of phosphate using a two-term Sellmeier dispersion formula are comparable with those of silica and fluoride single crystals. It is known, that UV radiation induces the generation of several defect centers leading to additional absorption bands. The investigation of the kinetics of defect generation is very important for the prediction of transmission losses in case of long-time irradiation. To predict the kinetics of defect generation, first the separation of absorption bands is necessary. Experiments were carried out using UV-lamps, the KrF excimer laser (ns- and fs-pulses) and the ArF excimer laser (ns-pulses). The healing behavior of radiation-induced absorption bands was investigated using thermal treatment (temperature-dependence) and bleaching experiments (radiation-dependence). The results of these experiments enable the separation of absorption bands and the prediction of the defect generation depending on the used radiation source. The healing of strong defects at room temperature is postulated to be a diffusion-controlled process.

Fluoride phosphate (FP) glasses with low phosphate content are high-transparent in the deep ultraviolet (UV) range and attractive candidates for UV-optics. Their optical properties are complementary to fluoride crystals. The anomalous partial dispersion makes them desirable for optical lens designs to reduce the secondary spectrum. Their UV transmission is limited by trace impurities introduced by raw materials and decreases when exposed to UV-radiation (lamps, lasers). The experiments of the paper published previously in this journal were used in order to separate radiation induced absorption bands in the fluoride phosphate glass FP10. In this paper the generation mechanism of the phosphorus–oxygen related hole center POHC 2 is investigated in detail in glasses of various compositions (various phosphate and impurity contents) in order to predict the transmission loss in case of long-time irradiation. Experiments were carried out using ArF- and KrF-excimer lasers (ns-pulses). POHC 2 generation strongly depends on the phosphate content and on the content of Pb 2+ . A model was developed on these terms. Rate equations are formulated, incorporating the influence of the Pb 2+ -content on the defect generation, a two-step creation term including an energy transfer process and a one-photon bleaching term. This results in a set of coupled nonlinear differential equations. Absorption coefficients and lifetimes of the excited states were calculated as well. Experimental results compared well with the numerical analysis of the theoretical rate equations.

Cerium, europium and terbium ions can exist in diAerent valencies in glasses. The formation and ultraviolet (UV) absorption features of the ions were studied in a fluoride phosphate (FP) and two phosphate glasses. Various melting conditions and X-ray irradiation were applied to change the redox states of the ions. Band separation of the UV absorption spectra was carried out to reveal the components and to determine their spectroscopic properties. The UV absorption spectra of the lower valent Eu 2a ,T b 3a and Ce 3a ions are due to 4f‐5d transitions, which are split in several bands by the local field around the rare-earth (RE) ions. The crystal field splitting of the trivalent ions diAers from the one of the divalent ion. The UV absorption spectra of the higher valent Eu 3a ,T b 4a and Ce 4a ions are caused by charge transfer (CT) transitions from oxygen and fluorine to the RE ions. The positions and oscillator strengths of the 4f‐5d and CT transitions are studied in dependence on the RE and glass type. Furthermore, the ligand field strength of Eu 2a ions is investigated. Redox tendency, site symmetry and charge of the RE ions are important factors considering the influence of the RE type. DiAerent polarizability and electron donor power of the ligands as well as diAerent RE site symmetry in the glasses cause the compositional dependence of the transition properties. ” 2000 Elsevier Science B.V. All rights reserved.

In this paper we report on measurements of the nonlinear refractive index n2 at 1047 nm of various fluoride- phosphate laser glasses relative to fused silica using degener- ate four-wave mixing. We find good agreement with empiri- cal estimates obtained from the d-line linear refractive index and the Abbe number for pure fluoride-phosphate glasses. Significant increase of n2 is observed when adding sulfate and niobium oxide to the glass composition offering tailorable nonlinear properties for glasses employed in short pulse laser oscillators.

High purity fluoride phosphate glasses are attractive candidates as UV transmitting materials. The calculated values for the ultraviolet resonance wavelength are comparable with those of pure silica glass or fluoride single crystal CaF2. The formation of radiation-induced defect centers leads to additional absorption bands in the VUV‐UV‐vis range. The damage and the healing behavior by lamps and lasers are investigated in dependence on phosphate content and the content of impurities, mainly transition metals. Experiments were carried out using pulsed lasers with a duration of femto- and nanoseconds at a wavelength of 248 nm. The initial slope of the induced absorption shows a nonlinear dependence on the pulse energy density. Resonant and non-resonant two-photon mechanisms were observed. Twophoton-absorption coeAcients at 248 nm for samples with diAerent phosphate contents were measured. Models of the kinetics of the radiation-induced defects were developed. The inclusion of energy transfer was necessary to explain the diAerence in the damage behavior for nanosecond (248 nm, 193 nm) and femtosecond (248 nm) laser pulses. ” 2000 Elsevier Science B.V. All rights reserved.

The relationship between intrinsic and extrinsic ultraviolet (UV) transmission and UV lamp- and laser radiation-induced defects produced in phosphate glasses has been investigated. The composition was varied from simple binary metaphosphate glasses (MPs) to multicomponent ultraphosphate glasses (UPs), which can be melted on a commercial scale, to small amounts of mono- and diphosphates in fluoroaluminate glasses. The effects of the structure-dependent band gap (intrinsic effect) and the Fe2+/Fe3+ and P5+/P3+/P0 concentration ratios (extrinsic effect) on the UV absorption, and on the formation and recombination of radiation-induced defects were studied. A correlation has been inferred with the optical basicity of the glass matrix. The kinetics of the photoionization of Fe2+ to (Fe2+)+ were measured and simulated. This process is single photon, whose rate depends on the phosphate content and increases with increasing phosphate content (increasing basicity). Single and two photon mechanisms were indicated by the excimer laser radiation forming electron and hole defect centers, which were attributed to phosphorus species based on their electron paramagnetic resonance spectra. These defects cause additional absorption bands in the UV-visible region. Differences were detected between phosphate and fluoroaluminate glasses with a phosphate content ⩽20 mol%. The fluoroaluminate glasses have the lowest optical basicity and are stable against UV radiation, but crystallize. The optical basicity increases, the crystallization tendency decreases, and the UV radiation-induced defects increase with increasing phosphate content.

Electron spin resonance (ESR) spectra of Eu2+ and Tb4+ were observed at room temperature in one fluoride phosphate and two phosphate glasses. Although both ions are isoelectronic, they have different ESR spectra. Eu2+ ions exhibit pronounced features at effective g-values of 2.0, 2.8 and 6.0, which is typical for the so-called U-spectrum. Tb4+ ions give only a single feature at g = 5.0. The different spectra are due to different crystal field strengths. The higher charge of Tb4+ ions results in a stronger local field compared with Eu2+ ions.

The two effects, covalency and asymmetry, on the Judd–Ofelt Ω2 parameter have been separated by use of Tb3+ 4f–5d absorption peak wavelength as a measure of covalency. According to the Judd–Ofelt theory, Ω2 increases with increasing reciprocal energy difference between the 4fN and 4fN−15d1 configurations. In fact, a linear correlation between Ω2 of Eu3+ and the peak wavelength of the Tb3+ 4f8 → 4f75d1 absorption band has been found for the fluoride, fluoride phosphate and phosphate glasses investigated. The differences in the peak wavelengths are caused by differences in the polarizability of the ligands, leading to differences in the covalency of the rare earth sites. This behavior is responsible for the sensitivity of Ω2 to the covalency of the bond between rare earth ions and their ligands. The deviation of the ultraphosphate glass investigated from the correlation between Ω2 and the Tb3+ 4f–5d peak wavelength is attributed to a higher degree of asymmetry of the local crystal fields around the rare earth ions.

Europium ions are used as indicators for defect center formation under X-ray and UV irradiation in a fluoride phosphate and an ultraphosphat e glass melted in air and under reducing conditions. Absorption and electron spin resonance spectroscopy is used to determine both intrinsic defect center formation and radiation-induced valence changes of europium ions. The effect of the europium ions on the defect center formation is studied in dependence on glass composition, melting condition and radiation source.

The effects of borosilicate glass composition and melting condition on valence state and coordination geometry of polyvalent Ti ions have been studied by X-ray absorption experiments. The results indicate that most of Ti 3+ ions are oxidized into Ti 4+ ions when Ti 2 O 3 is doped into sodium borosilicate glasses. When TiO 2 is doped into sodium borosilicate glasses, almost all of titanium ions are in the form of Ti 4+ . Doping both graphite and titanium oxide simultaneously in borosilicate glasses favors the formation of small amounts of Ti 3+ ions. Ti 4+ ions occupy both fivefold and sixfold coordinated sites in borosilicate glasses with non-bridging oxygen (NBS1), mainly fivefold coordinated sites. For borosilicate glasses without non-bridging oxygen (NBS2), Ti 4+ ions are in both fourfold and fivefold coordinated sites. Using reducing agents during melting procedure favors the formation of fourfold coordinated Ti 4+ ions in NBS2.

Glass, although known for thousands years, has been heavily investigated in the past few years. This was mainly caused by the demand on advanced materials for optics and optoelectronics. Here, active laser glasses and glasses for laser optics especially for the deep W-range played an important part. Other important developments were glass fibres for various wavelengths and optoelectronic devices, such as waveguides. Additionally, new glass ceramics have focused a great deal of interest. Besides those glass ceramics possessing extremely low thermal expansion, glass ceramics for biomedical applications, e.g. as material for human bone replacement as well as oriented glassceramics have intensively been studied.

The relationships between glass structure and spectroscopic properties of the doped ions Eu3+ and Tb3+ are of interest. Eu3+ and Tb3+ ions are used as structure-sensitive ions. The Ω t - parameters of Eu3+ were determined from absorption and emission spectra. The lifetime of the 5D0 state of Eu3+ was calculated from Ω t and compared with the experimentally determined lifetime. The electron-phonon coupling strength and phonon energy were obtained from phonon sideband spectroscopy. The f → d absorption transition of Tb3+ was used for determination of the nephelauxetic parameter. With increasing phosphate content the covalency between rare earth ions and surrounding ligands increases due to substitution of fluoride ions by oxygen ions having higher electron polarizability. This effect leads to increasing nephelauxetic shift, Ω 2 - parameter and electron-phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions.

Fluoride phosphate glasses are attractive candidates as ultraviolet-transmitting materials. It is important to know their resistance to radiation damage by excimer laser illumination. One fluoride phosphate glass (35 AlF 3 , 30 CaF 2 , 15 SrF 2 , 10 MgF 2 , 10 Sr(PO 3 ) 2 (mol%)) of high purity and doped with metal ions, Fe, Cu, Ce, Pb, was irradiated by excimer laser illumination at 193 and 248 nm. The samples were melted under oxidizing, normal and reducing conditions to change the redox state of the doped ions. Absorption and fluorescence spectra of the samples were measured before and after irradiation. From the radiation-induced changes in the absorption and fluorescence spectra, the following conclusions were obtained. Irradiation induces a photo-oxidation of the lower valence ions. The formation of hole centers is suppressed in samples doped with Fe and with 1000 ppm Ce, respectively, but it is intensified in samples doped with Pb, Cu and Ce up to 100 ppm. The formation of electron centers depends on the concentration of lower valence ions before irradiation. The radiation-induced effects are strong if the wavelength of the excimer laser radiation is in the range of strong absorption bands of the lower valence ions.

High purity fluoride phosphate glasses FP 10 (35 mol% AlF 3 , 30 CaF 2 , 15 SrF 2 , 10 MgF 2 , 10 Sr(PO 3 ) 2 ) with a large transmission range from the vacuum ultraviolet to the infrared were doped with polyvalent metal ions (Fe, Cu, Ce, Cr, Pb, Ni) in the ppm range. Their redox behaviour was investigated under normal and strong reducing melting conditions depending on temperature. Only one redox state was observed for Ni 2+ and Pb 2+ . From the other metals, the following redox equilibria could be detected : Fe 3+ /Fe 2+ , Ce 4+ /Ce 3+ , Cu 2+ /Cu + /Cu 0 , Cr 3+ /Cr 2+ . A linear relation between the log C ox /C red and 1/T was found in the temperature range 900-1200°C. In samples melted under normal conditions in air atmosphere, the higher redox state dominates but is strongly affected by the raw materials. By reducing melting conditions, the redox equilibrium could be shifted more than 99.5% to the lower oxidation state, Fe 2+ , Ce 3+ and Cu + . Absorption, luminescence excitation and emission spectra were used detect Ce 3+ , Cu + , Pb 2+ and Cr 3+ to low quantities (< 0.1 ppm).

Fluoride-based glasses are potential host materials for fiber lasers, amplifiers and solid state three-dimensional (3D) displays. Fluorozirconate (ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF), fluoride phosphate (AlF 3 -SrF 2 -CaF 2 - MgF 2 -P 2 O 5) and fluoroin­ date (InF 3 -ZnF 2 -BaF 2 - GaF 3 -PbF 2 -REF 3 -S rF 2 -NaF-CaF 2) glasses were investigated in terms of their absorption and crystallization properties to compare their potential to be used as optical devices. Phonon sideband (PSB) measurements were employed to determine the local vibration behavior of the rare earth (RE) ion sites. A modified Judd-Ofelt treatment allows the description of transition probabilities between Pr 3+ energy levels, including error estimates for the fitted parameters Ω,. In the investigated fluoroindate glasses melted in vitreous carbon crucibles using a reactive atmosphere, processing fanlike crystals composed of Sr and RE fluorides caused manufacturing problems.

The effect of Nd3+ and hydroxyl group concentration, as well as the effect of glass composition on the relaxation processes of excited Nd3+ ions, are studied for various phosphate glasses and a fluoride phosphate glass. The relaxation of the 4F32 level of the Nd3+ ions is dominated by radiative decay, energy transfer to hydroxyl groups and cross-relaxation. Lifetime measurements of this level as a function of hydroxyl group and Nd3+ concentrations lead to a resolution of the individual relaxation processes. Based on this analysis, the relationships between the glass matrix and the concentration quenching and radiative decay rate, respectively, are studied. Finally, the contributions of the individual relaxation processes to the lifetime of the 4F32 level are compared with each other in different glass types.

Fluoride phosphate glasses are attractive candidates for high-performance glass for the deep ultraviolet range. The calculated values for the ultraviolet resonance wavelengths 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, mainly transition metals. The influence of the redox states of Fe, Cu, Pb and Ni in the ppm range on the ultraviolet absorption was investigated. The individual absorption coefficients per ppm ion and the redox equilibria resulting from the melting conditions and refining temperature were determined. Fe3+, Cu2+ and Pb2+ have the largest influence on the ultraviolet absorption. Glasses melted under reducing conditions have much higher ultraviolet transmission at 250 nm than glassees melted under oxidizing conditions. The ultraviolet absorption of the glass is strongly dependent on the reducing temperature. The ultraviolet absorption decreases and the luminescence increases drastically with increasing reducing temperature from 850 to 1100°C. The redox equilibria are shifted to Fe2+ and Cu+, over 1100°C towards Cu0 colloids too. The molar absorption coefficients in the ultraviolet range of the lower redox states are more than one order lower than those of the higher redox states.

For several phosphate glass systems composed of K2O, SrO, (La, Nd)2O3 and P2O5, different dehydration methods have been investigated: variation of raw materials, addition of halides, sintering of raw material mixtures, remelting of glasses, variation of melting time, bubbling of dry oxygen. The methods have been compared with each other concerning their effect on decreasing the OH content. Further, a model of the interactions between glass melt and atmosphere has been established for glasses prepared using fluoride addition or not.