V. V. Koltashev

On the structure of phosphosilicate glasses

Abstract Vibrational spectra of phosphosilicate glasses with P 2 O 5 concentrations up to 15 mol% are investigated by the methods of Raman spectroscopy and quantum-chemical modeling. We have found that the Raman band at 1320 cm −1 characteristic for such glasses is not simple and may be decomposed into two components with frequencies at ≈1317 and ≈1330 cm −1 caused in our opinion by single phosphorus centers (OPO 3 tetrahedra surrounded by SiO 4 ones) and by double phosphorus centers (pairs of OPO 3 tetrahedra bonded by a common oxygen atom). In the investigated phosphosilicate glasses manufactured by MCVD and SPCVD methods the ratio of concentrations of single and double centers varies from 1:5 to 1:2. A novel interpretation of the Raman bands distinct from the traditional one is suggested. The approach to the Raman spectra analysis developed in this article can be applied for control and optimization of manufacturing process of phosphosilicate and similar glasses as well as optical fibers.

Raman band intensities of tellurite glasses

Raman spectra of TeO2-based glasses doped with WO3, ZnO, GeO2, TiO2, MoO3, and Sb2O3 are measured. The intensity of bands in the Raman spectra of MoO3-TeO2 and MoO3-WO3-TeO2 glasses is shown to be 80-95 times higher than that for silica glass. It is shown that these glasses can be considered as one of the most promising materials for Raman fiber amplifiers.

UV-irradiation-induced structural transformation of germanoscilicate glass fiber

Raman spectra of germanosilicate core fibers before and after UV irradiation were investigated. Significant changes of the Raman spectra after irradiation indicate transformation of the glass structure. A possible interpretation of the observed changes is proposed.

Centres of broadband near-IR luminescence in bismuth-doped glasses

Interstitial negative-charged bismuth dimers, and , are suggested as a model of broadband near-IR luminescence centres in bismuth-doped glasses. The model is based on quantum-chemical calculations of equilibrium configurations, absorption, luminescence and luminescence excitation spectra of the dimers in an alumosilicate network and is supported by IR and visible luminescence observed for the first time in bismuth-doped polycrystalline magnesium cordierite and by Raman spectra measurements in optical fibres with bismuth-doped alumosilicate glass core.Interstitial negative-charged bismuth dimers, and , are suggested as a model of broadband near-IR luminescence centres in bismuth-doped glasses. The model is based on quantum-chemical calculations of equilibrium configurations, absorption, luminescence and luminescence excitation spectra of the dimers in an alumosilicate network and is supported by IR and visible luminescence observed for the first time in bismuth-doped polycrystalline magnesium cordierite and by Raman spectra measurements in optical fibres with bismuth-doped alumosilicate glass core.

High-Purity As-S-Se and As-Se-Te Glasses and Optical Fibers

We describe a procedure for the preparation of As-S-Se and As-Se-Te glasses with low contents of gas-forming impurities (hydrogen, oxygen, and carbon) via melting of extrapure-grade elements in an evacuated silica ampule and purification of the melt by chemical distillation. The impurity concentrations in the glasses thus prepared have been reduced to the following levels: hydrogen, <0.02; oxygen, 0.2; carbon, <0.02; silicon, <0.4 ppm by weight. Using the double-crucible method, we have fabricated glass fibers with various ratios of the core and cladding diameters (1: 25 to 9: 10), protected with a tetrafluoroethylene/1,1-difluoroethylene copolymer coating, which have an average bending strength of 0.5–1 GPa. The minimal optical losses are 150 dB/km at 6.6 μm in multimode As-Se-Te glass fibers and 60 dB/km at 4.8 μm in As-S-Se glass fibers. The effect of microinhomogeneities in the melt on the optical performance of arsenic sulfoselenide glass fibers fabricated by the double-crucible method is examined.

Low-frequency band at 50 cm-1 in the Raman spectrum of cristobalite : identification of similar structural motifs in glasses and crystals of similar composition

Abstract Raman spectra of high-temperature α-cristobalite ceramics and silica glass have been obtained in a wide frequency range from 10 to 1500 cm −1 . A low-frequency maximum at 50 cm −1 in the spectrum of cristobalite has been observed to be similar to the well-known band at 52 cm −1 in the Raman spectra of silica glasses. The combination of literature reports on inelastic neutron scattering, low-temperature heat capacity, X-ray and neutron scattering in the region of the first sharp diffraction peak (FSDP) and our data on Raman and far IR spectroscopies indicate a cristobalite-like medium-range order in silica glasses. The comparison of the obtained spectra with the Raman spectrum of α-quartz, as well as the comparison of far IR spectra of some multicomponent glasses with the ones of corresponding crystals, demonstrates that by means of low-frequency spectroscopic data it is possible to identify the crystalline polymorphs reflected by the glass.

Origin of microinhomogeneities in As-S-Se glass fibers fabricated by the double-crucible method

The optical losses in sulfoselenide glass fibers fabricated by the double-crucible method are shown to rise in going from the first-drawn portion to the back end of the fiber. Optical microscopy, IR and Raman spectroscopy, energy-dispersive x-ray microanalysis, and differential scanning calorimetry data indicate that fiber drawing is accompanied by the development of microinhomogeneities of the chemical and phase compositions of the melt, which are responsible for the increased scattering losses. The microinhomogeneities originate from phase segregation of the molten glass.

UV irradiation-induced structural transformation in phosphosilicate glass

The Raman spectra of phosphosilicate core (P(2)O(5)-SiO(2)) fibers were investigated. Significant changes in the spectra were observed after UV irradiation of the fibers. An interpretation of the photostructural changes confirmed by computer simulation of phosphorus-related centers is proposed.

Solubility of nitrogen, carbon, and hydrogen in FeO–Na2O–Al2O3–SiO2 melt and liquid iron alloy: Influence of oxygen fugacity

Abstract—Reactions of nitrogen, carbon, and hydrogen with FeO–Na2O–Al2O3–SiO2 melts, liquid iron alloys, and graphite were investigated at 4 GPa, 1550°C, and fO2 values 1.5–3.0 orders of magnitude below fO2(IW). A number of features important for the understanding of the formation conditions of volatile nitrogen compounds during melting of the Earth’s early reduced mantle were revealed. The nitrogen content of melt increases with decreasing fO2 from 0.96 wt % at ΔlogfO2(IW) =–1.4 to 4.1 wt % at ΔlogfO2(IW) =–3.0, whereas the hydrogen content of melt is weakly dependent on fO2 and lies within 0.40–0.47 wt %. The carbon content is approximately 0.3–0.5 wt %. The IR and Raman spectroscopy of the glasses indicated that the dissolution of nitrogen, carbon, and hydrogen in silicate liquids is accompanied by the formation of NH3, N2, and CH4 molecules, as well as NH2–, NH2+, NH4+ and CH3– complexes. Hydrogen is dissolved in melts as OH–, H2O, and H2. The experiments also demonstrated the presence of species with C=O double bonds in the melts. It was found that the solubility of nitrogen in FeO–Na2O–Al2O3–SiO2 melts increases in the presence of carbon owing to the formation of species with C–N bonds in the silicate liquid. One of the most remarkable features of nitrogen, carbon, and hydrogen interaction with FeO–Na2O–Al2O3–SiO2 melts is a significant change in the proportions of N–C–H–O species at fO2 2–3 orders of magnitude below fO2(IW). Under these conditions, a sharp decrease in the contents of NH4+, NH2+ (O–NH2), OH, H2O, and CH4 is accompanied by enrichment in NH2– (=Si–NH2) and NH3. As a result, NH3 becomes the dominant nitrogen species in the melt. The investigation revealed high nitrogen solubility in iron alloys at fO2 < fO2(IW). The nitrogen content increases from 2.47 wt % at ΔlogfO2(IW) =–1.4 to 3.63 wt % at ΔlogfO2(IW) =–3.0. The carbon content of N–C–Fe alloys ranges from 2.3 to 3.8 wt % and decreases with decreasing fO2. The siderophile behavior of nitrogen at fO2 < fO2(IW) suggests that part of nitrogen could be dissolved in iron alloys during large-scale melting of the early reduced mantle with subsequent nitrogen burial in the Earth’s metallic core. It was suggested that the self-oxidation of magmas in the Earth’s early mantle with the release of reduced N–C–H–O volatiles could be one of the reasons of extensive nitrogen degassing.

Low-loss, high-purity (TeO2)0.75(WO3)0.25 glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO2)0.75(WO3)0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 102 cm−3, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm−1. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.