Optical spectra of glasses

This presentation focuses on several ways in which structural and dynamical information can be obtained from optical spectroscopy by examining results of infrared and Raman studies of selected oxide glasses. Though these studies represent only a small fraction of the work on most of the glasses mentioned, and many other important forms of optical spectroscopy are not treated here, they illustrate useful approaches to the study of amorphous materials by optical methods.     

Optical attenuation in titania-silica glasses

The bleaching of bulk titania-silica glasses in the annealing temperature range is investigated. The sample-size kinetics can be predicted from the hydrogen diffusion coefficient. Hydrogen gas is evolved from both titania-silica and silica glass but in larger amount from the former. In the bleaching process, Ti³⁺ ions disappear from the titania-silica glass. These results are consistent with the coloration caused by Ti³⁺ which is oxidized by OH- in the glass to produce gaseous hydrogen.     

Optical properties of selenite glasses

The aim of this work is to obtain multicomponent selenite glasses containing other non-traditional glass formers such as V₂O₅, TeO₂ and MoO₃ and to verify their optical properties in the visible spectral region. Glasses containing MoO₃ and TeO₂ are transparent in the visible range and near IR region from 400 to 2300 nm. Transparent coloured glasses were obtained due to the electron transfer charge processes. Using IR spectroscopy it was determined the main building units of the amorphous network. It was found the presence of TeO₄, SeO₃ and MoO₄ units.     

Optical properties of chalcogenide glasses

Over the past two decades chalcogenide glasses have been researched in order to assess their suitability as passive bulk optical component materials for 3–5μm and 8–12μm infrared applications. This research has led to a greater understanding of the physical properties of these materials, and the present paper concentrates on the optical properties and applications of these bulk chalcogenide glasses. The various factors influencing the intrinsic and extrinsic optical loss mechanisms in materials are discussed, numerical data on the basic optical properties of chalcogenide glasses is presented and applications are discussed.     

Optical properties of erbium-doped fluorochlorozirconate glasses

We report the optical properties of a fluorochlorozirconate (FCZ) glass with the composition 53% ZrF₄, 20% NaF, 3.5% AlF₃, 3% LaF₃, 0.5% InF₃, (20 ? x)% BaCl₂, x% BaF₂ with x varying from 0% to 2%, and doped with various amounts of trivalent erbium by the addition of ErCl₃. Annealing of the as-prepared glass in inert (N₂) or reducing (5%H₂ + 95%Ar) atmospheres at temperatures that ensure the conversion of the glass into a glass-ceramic by the nucleation of BaCl₂ nanocrystals, does not significantly change any of Er³⁺ related absorption and photoluminescence (PL) characteristics. We have carried out a Judd–Ofelt analysis of the absorption spectra and obtained Ω₂ = (1.92 ± 0.3) × 10^? 20 cm², Ω₄ = (0.88 ± 0.16) × 10^? 20 cm² and Ω₆ = (0.59 ± 0.08) × 10^? 20 cm², and also the radiative lifetimes of the ⁴I_13/2→⁴I_15/2, ⁴I_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 bands. The radiative lifetime from the Judd–Ofelt analysis for the ⁴I_13/2→⁴I_15/2 band is in good agreement with the experimentally measured PL decay time. The examination of the optical properties of powdered samples with different average particle size does not show any photon trapping effects. We have determined the spectral absorption and emission cross-sections and then estimated the possible spectral optical gain for varying degrees of relative populations of the ⁴I_13/2 and ⁴I_15/2 manifolds.     

Optical spectra of sodium phosphate glasses

The visible, infrared, and ultraviolet spectra of seven glasses in the Na₂OP₂O₅ binary system were obtained. Changes in spectra were related to structural changes occurring the glass. Dopant ions Co²⁺, Cu²⁺, and Pb²⁺ were used to infer structural changes occurring as the metaphosphate composition was crossed going from pyrophosphate compositions into ultraphosphate compositions. The presence of chemically bound water was found to cause the overall modifier-to-former ratio to remain constant for glasses containing greater than 65 mol.% P₂O₅.     

The structure of some chalcogenide glasses

A study using replica electron microscopy, scanning electron microscopy, electron diffraction, X-ray diffraction, sputter etching and differential thermal analysis of the structural properties of glasses having a range of compositions within the AsTeGeSi quaternary system has shown that phase separation generally occurs in the bulk material. The second phase is dispersed as inclusions in the non-crystalline matrix and is apparently non-crystalline away from the boundary of the glass forming region but is crystalline near to the high Te boundary. The crystalline second phase is probably Te. This quaternary system, AsTeGeSi is often used as source material for the fabrication of devices studied for their monostable electrical switching behaviour and the phase separation observed in these materials needs to be considered in the interpretation of the switching properties and for failure analysis of such devices.     

Optical and structural properties of Sr-Nb-phosphate glasses

This research studied optical and structural properties of SrO-Nb₂O₅-P₂O₅ glasses containing 0 ~ 25 mol% Nb₂O₅ and 35 ~ 60 mol% SrO using spectra of UV-Vis, FTIR and XPS. Our aim was to work new moldable glasses which are colorless with high refractive index and transmittance, and their correlation with glass structure. Nb₂O₅ plays the role as an intermediate of glass formation, and transforms the role to network-former or glass-modifier depending on composition. Refractive index increases monotonically with Nb₂O₅ content at the expense of transmittance, and specific coloring which occurs in ternary compositions with the ratio P₂O₅/SrO > 1. This effect arises from much increased [Nb³⁺ and Nb⁴⁺] fraction, as quantitatively deconvoluted in Nb3d XPS spectra, in the ligand [NbO₆]_octahedral which is supported by FTIR and O1s XPS spectra. As the ratio P₂O₅/SrO ≤ 1, Nb₂O₅ is more of a network former and [NbO₆]_octahedral structure turns into [NbO₄]_tetrahedron with partial Nb-O…(Sr) bonding turns into (Nb-O-Nb)_tetrahedron, coloring disappears.     

Optical and spectroscopic properties of germanotellurite glasses

In this work, new glass compositions in the TeO₂-GeO₂-Nb₂O₅-K₂O system have been prepared and studied. The germanotellurite glasses were prepared by melt-quenching and their density, refractive index and characteristic temperatures have been determined. The structure of these glasses has been studied by infrared and Raman spectroscopies.The progressive replacement of TeO₂ by GeO₂ led to an increase of the glass transition and crystallisation temperatures of the glasses and a simultaneous decrease of their density and refractive index. Typical density and refractive index values of these glasses ranged from 4.98 to 3.85 g cm^− 3 and 2.08 to 1.79, respectively, with increasing GeO₂ content. The infrared spectra are dominated by a band ~ 640 cm^− 1 in the tellurite glass and ~ 800 cm^− 1 in the germanate glass. The Raman spectra of the germanotellurite glasses present an intense boson peak between ~ 34 and 47 cm^− 1, together with high frequency peaks at ~ 670 cm^− 1 and ~ 470 cm^− 1 for high tellurite and high germanate glass compositions, respectively. The vibrational spectra of these germanotellurite glasses indicate that the glass network consists basically of TeO₄ and [TeO₃]/[TeO_3 + 1] units, mixed with GeO₄ and NbO₆ polyhedra.     

Optical properties of zinc barium silicate glasses

A serial of glasses samples with the higher ZnO concentration from 30 mol% to 45 mol% were prepared and their optical absorption and photoluminescence properties were investigated. It is shown that the composition of glass strongly affects the position of the absorption edge and emission band where a fairly big red-shift was observed with increasing of ZnO concentration. It is most likely attributed to the reduced quantum confinement effect due to increased aggregation degree of ZnO in the glass matrix. The introduction of F^? into zinc barium silicate glasses leads to a notable red-shift of the absorption spectra, as well as the enhanced UV emission and distinctive visible emissions.     

Optical properties of zinc molybdenum phosphate glasses

Zinc molybdenum phosphate (ZnO–MoO₃–P₂O₅) glasses of different compositions were prepared and synthesized and some of their properties were studied. The optical band gaps have been deduced from spectral dependence curves. The infrared absorption spectra of these investigated glasses were found analogous to SrO–Fe₂O₃–P₂O₅. Annealing at different temperatures does not show a prominent change in absorption band positions. We correlate our findings with a possible structural explanation of these glasses.     

Optical and electrical properties of Tl-S glasses

The frequency and temperature dependence of ac conductivity and optical absorption have been measured for four Tl-S glasses, TlS, Tl₂S₃,TlS₂ and Tl₂S₅, prepared by a melt-quenching method. The ac conductivity has been measured over a frequency range 0.1 Hz to 1.8 GHz and a temperature range 190-273 K. The optical absorption was measured at room temperature over a wavelength range 200-2600 nm. We have determined the electrical and optical band gaps from the experimental results. For each glass, the electrical band gap is larger than the optical band gap and the difference increases with increasing sulfur concentration. The frequency dependence of ac conductivity varies with composition of the glasses. We suggest that these results are due to an increase of localized states in the band gap with increasing sulfur concentration.     

Sub-critical crack growth in some phosphate glasses

The effect of alumina on the sub-critical crack growth is investigated on a set of calcium aluminophosphate glasses of molar composition 50% P₂O₅–(50 ? x)% CaO–x% Al₂O₃ (0% ? x ? 10%). The crack propagation is operated using the double-cleavage-drilled-compression (DCDC) method. In this test, the sample is loaded in compression with a mechanical testing machine in an environmentally controlled chamber (both temperature and water vapor pressure). The crack velocity is plotted as a function of stress intensity factor. Regions I and II are characterized by a dependence of crack velocity on the amount of alumina content in the glass. When the alumina content increases, glass shows, as expected, a trend less sensible to the stress corrosion correlated to the slope of the crack growth curves, but in the same time, these curves are shifted toward higher crack velocity values. For different compositions, an unexpected behavior is also observed with temperature and water vapor pressure. We assume the formation of a ‘gel-like product’ on fresh fracture surfaces which modifies the reactivity at the crack tip.     

Elastic properties of some bulk metallic glasses

The relationships between the elastic moduli, glass forming ability and response to deformation of bulk metallic glasses are investigated. Five bulk metallic glasses are prepared from high purity elements via suction casting. The results confirm that there exists a correlation between energy absorbed to failure during compression testing and the bulk to shear modulus ratio. This finding is developed such that it corresponds only to the elastic component of energy absorption, and that the bulk modulus dominates this. Plastic deformation appears to be favored by a reduced shear modulus, although it shows greater dependence on structural features that are frozen in during the glass transition, and so may well be dependent on the liquid fragility.     

Infrared absorption of some high-purity chalcogenide glasses

New compouning techniques were devised to prepare high-purity Ge₂₈Sb₁₂Se₆₀ (TI 1173)and Ge₃₃As₁₂Se₅₅ TI 20). The methods were based on the combination of the reactant purification and compounding steps. The goal of the program was to establish the absorption limit for the glasses and to lower the absorption at 10.6 μm. At the present purity level, the GeSbSe glass is found to have an absorption level of about 0.01 cm^?1 at 10.6 μm while the absorption level for the GeAsSe glass is 0.05 cm^?1. Underlying causes for the limits are discussed along with the possibilities for improvement.     

The thermal conductivity of some chalcogenide glasses

The temperature-dependent thermal conductivities of several chalcogenide glasses were determined above 300 K. At 300 K, the thermal conductivity for most of these glasses is about 3 mW/cm · deg.     

Optical and structural properties of calcium silicate glasses

A detailed analysis of the reflectance and transmittance spectra of a set of glasses allowed retrieval, besides the optical functions, of quantitative information on the structural changes occurring in the calcium silicate glass system. The occurrence of a threshold around 46% of CaO content is confirmed and is connected to the appearance in the glass structure of a new configuration of calcium cations. It was also shown that the calcium cations that exceeds the compositional threshold does not act as modifiers of the silicate network since they form Ca–O–Ca bonds in the glass structure. Obvious changes occurring at the threshold in the physical or chemical properties can be understood in the light of the structural changes observed in the system.     

Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi₂O₃-P₂O₅ glass with low-P₂O₅ content (20-25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF₂. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF₂ substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s-6p interband transition in Bi³⁺ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.     

Optical and structural properties of new chalcohalide glasses

New class of chalcohalide glasses has been prepared in the GeS₂–In₂S₃–CsI system with regard to their potential non-linear properties. The study of glass-forming region was undertaken to select glassy compositions, which present high non-linear (NL) optical properties with a low two-photon absorption. Thermal analyses, structural examination by Raman spectroscopy, non-linear optical measurements were investigated as a function of CsI contents. Introduction of CsI has shifted the band-gap edge towards the blue region of the absorption optical spectrum and therefore has limited the two-photon absorption. Their NL refractive index n₂ are 60 times higher than silica glasses without any NL absorption. Moreover, second harmonic signal was observed in thermally poled samples similar to silica glass. However, this second order non-linearity is not temporally stable.     

Optical properties of porous glasses doped with ZnS

The paper presents a new preparation method to form semiconductor nanoclusters inside silica porous glasses as matrices and describes investigations of the luminescence properties of the samples loaded repeatedly with ZnS nanoparticles. Silica porous glasses were obtained by leaching the two-phase sodium borosilicate glasses in acid solution. The samples consisting of two types of glasses with different pore sizes and immobilized nanosized ZnS in these matrices by a chemical deposition process were used. EDS measurements confirmed purity of the samples. The recorded absorption and photoluminescence spectra exhibit the quantum size effect due to the increasing number of the chemical deposition cycles.