Multicomponent Silicate Glasses Research Articles

High-Rate Deposition Of Rare-Earth Doped Silicate Nanoparticles For Porous & Dense Optical Films

AbstractA novel deposition process has been developed for manufacturing of high quality rare-earth doped glass films with complex composition. This process, Laser Reactive Deposition (LRDTM), comprises photothermal laser pyrolysis using an aerosol feedstock coupled with deposition of the resulting nanoparticle product onto Si substrates with our without an underlying glass film. This paper describes this novel process as well as the structure, properties and performance of the Erdoped, multicomponent silicate glass films produced to date with this process.

Photosensitive properties of a tin-doped sodium silicate glass for direct ultraviolet writing

In this letter, the fabrication of channel waveguides by direct UV writing into a bulk tin-doped multicomponent silicate glass is presented. Different laser powers and scan rates were employed and optimized to avoid surface ablation. The best results were obtained at a laser power of 95 mW and at a scan speed of 10 mm/min, where a refractive index change of 1.5×10−3 was estimated and an attenuation loss of 3.3 dB/cm was measured using the cutback method. A morphological investigation of the glass end facets was performed in order to assess the surface effect of the laser exposure.

Radiation-induced nonsteady-state absorption in multicomponent silicate glasses

Nonsteady-state absorption spectra have been studied in multicomponent glass F1 of the flint group and its radiation-stable analog F101, induced by excitation with an electron pulse 20 ns wide having particle energy 0.25 MeV. The measurements were made in the 300-600 nm spectral region on the time interval 10 ns-1 sec after the end of the irradiation pulse. It is found that the formation efficiency of unstable color centers with absorption bands in this spectral region is approximately identical for both types of glasses. After the pulse stops acting, the absorption in the entire spectral range decreases at approximately the same rate, so that the shape of the nonsteady-state induced absorption spectra shows little variation. The effect of the cerium ions that are present in F101 as a protector additive manifests itself in times much greater than the pulse width. © 2004 Optical Society of America

Chemical Reactions Occurred in Oxide Glasses and Their Melts and Evaluation by Acid-Base Concept: NMR Investigation of Multi-Component Silicate Glasses

Multi-component silicate glasses containing alumina and alkaline earth metal oxides have been used for optical glasses. In these glasses competitive reactions between various kinds of network-forming and network-modifying oxides occur, so that it is effective to differentiate these reactions in terms of an acid-base concept. In this report the reactivities of alkali or alkaline earth oxide with P2O5, Al2O3, B2O3 and SiO2 are discussed based on the result of high-resolution solid state NMR. In alkali aluminoborosilicate glasses the population of four-coordinated boron atom, N4 are expressed well by r/(1-r). However, in the case of alkaline earth aluminoborosilicate glasses, the deviation from the line of r/(1-r) increases in the order of BaO<SrO<CaO<MgO, where r=([M2O] or [MO]-[Al2O3])/([M2O] or [MO]-[Al2O3]+[B2O3]). Alkaline earth oxide reacts with Al2O3 first. Subsequently, residual one reacts with B2O3 or SiO2. Weak base such as MgO reacts mainly with weak acids such as SiO2 rather than B2O3. On the other hand, a strong base such as BaO reacts mainly with B2O3. The equilibrium constant of the reaction, Si (Q3)+B(Q3)=Si(Q4)+B(Q4), can be determined. When K2O and CaO are contained in aluminoborosilicate glasses, it is possible to predict the distribution of the structural units by using the equilibrium constant of individual basic oxide.

Photosensitivity of germanium-doped multicomponent silicate glasses: role of boron and sodium ions

Photosensitive, germanium-doped multicomponent silicate glasses were prepared and submitted to electron paramagnetic resonance measurements. Spectral data were recorded before and after UV excimer laser irradiation at an emission wavelength of 248 nm at various energy doses. A particular attention was devoted to the analysis of defect signal intensities and characteristics, by performing saturation plots, intensity decay spectra versus time and temperature, with the aim of studying the structural changes involved in laser irradiation, which lead to a refractive index change, exploited for telecom and sensor applications. The main results showed that the presence of boron and the absence of sodium play a role in the type and the number of defects, their time and thermal decay, always keeping constant the UV exposure of the glasses. Consequently, the presence, the absence and the co-presence of these two ions may have a role in the photosensitivity of the glasses. It is important to understand the role of both, particularly the role of sodium on the photosensitivity of germanosilicate and germano-boro-silicate glasses, for their interest in the field of ion-exchangeable glasses for photonic waveguides and Bragg-grating based devices.

TEM studies of silver nanoparticles in phase-separated soda lime silicate glasses

Transmission electron microscopy (TEM) was used to characterise the microstructure of a phase-separated soda lime silicate glass in which sodium was partially substituted by silver during the ion exchange process. To transform the dopant ions into nanosized particles of colloidal silver, high-temperature annealing (in air and hydrogen) and irradiation (γ-rays from a 60Co source) were used. It has been stated that both treatments affect not only the dopant ions but also the morphology of the matrix. A variety of the induced changes could be exploited for new applications of multicomponent soda lime silicate glasses.

The Microstructure of Soda-Lime Silicate Glasses Detected by Electron Microscopy

Transmission electron microscopy and selected area electron diffraction performances were used to characterise the microstructure of a multicomponent soda-lime silicate glass, the composition of which corresponds to the miscibility gap in the SiO2—Na2O system. It has been stated that phase separation already exists in as prepared specimens, and the Na2O-rich phase occurs in the form of nearly spherical droplets. The microstructure of these glasses was modified by high-temperature annealing in air and hydrogen, by irradiation with soft X- and gamma-irradiation and by mechanical stretching. In this way the quantity, size, shape and distribution of these particles was changed. A variety of induced changes affects the structure-sensitive properties of commercial soda lime silicate glasses, which can be potentially useful for new applications.

Structure of Thin Films of Binary and Multi-Component Lead Silicate Glasses on Metals

The topography and composition of surface layers in thin films of lead silicate glasses obtained by thermodiffusion homogenization on metal substrates is investigated. The composition of the film – substrate transitional layer is analyzed.

Microstructure and silver nanoparticles in ion-exchanged and deformed soda-lime silicate glasses

Optical absorption, microspectrophotometry, thermally stimulated depolarization current, and transmission electron microscopy were applied to a commercial multicomponent soda-lime silicate glass subjected to the Na +⇔Ag + ion-exchange, annealing in air or hydrogen, and to mechanical stretching. The treatments affect both the matrix microstructure and the morphology of the silver particles. Mechanical stretching of the exchanged specimens annealed in hydrogen induces the most interesting effects. Secondary phase separation occurs within the glassy matrix, and causes drastic changes of the thermocurrent data, which are interpreted in terms of the Maxwell–Wagner interfacial polarization. Elongation of the spherical silver nanoparticles produces a remarkable dichroism of the optical absorption, which could be exploited for new applications. The sample stretching affects only particles with a diameter larger than 5 nm interpreted as a threshold size, at least at the stresses used in the present work.

Determination of the limiting fictive temperature of silicate glasses from calorimetric and dilatometric methods: Application to low-temperature liquid volume measurements

The limiting fictive temperatures (T f ') of 16 multi-component silicate glasses have been derived quantitatively from heat capacity measurements, following the method of Moynihan et al. (1976). These quantitative values of T f ' closely match temperatures corresponding to the onset (T onset ) of the rapid rise in dilatometry heating curves (dL/L vs. T) at the glass transition, obtained on glasses with similar cooling histories. The mean deviation (T f '- T onset ) is 5 K, whereas the maximum deviation is 17 K. These results confirm that the T f ' of a silicate glass can be determined from the T onset of a glass dilatometry curve with an uncertainty that is &lt;20 K. An application of the T f ' measurements includes the precise determination of the specific volumes of supercooled liquids at their respective T f ' values (Lange 1997). By comparison with other measurements in the literature, the accuracy of the T f ' method for determining low-temperature, fully relaxed, supercooled liquid volumes is shown. A comparison of volume-temperature models in the literature shows that a linear model (where thermal expansivity is independent of temperature) provides a superior fit of measured volumes in the SiO 2 -Al 2 O 3 -MgO-CaO-Na 2 O-K 2 O system over very wide temperature intervals (700-1900 K).

High field electron paramagnetic resonance of Gd3+-doped glasses: Line shapes and average ion distances in silicates

The average distances between Gd3+ ions in multicomponent silicate glasses doped with 0.058 to up to 4.64 wt % Gd2O3 are characterized by electron paramagnetic resonance (EPR) line broadening effects at high-field (95 GHz, W band). Increase in the EPR resonant field/frequency above that of the conventional X band (9.5 GHz) simplifies the Gd3+ EPR spectra and increases the sensitivity of the EPR linewidth to concentration induced broadening effects. Least squares line shape simulations show that the broadening can be described by a Lorentzian function with a width proportional to the average Gd3+ concentration which is in good agreement with the existing theories. Analyses of the concentration dependence of Lorentzian line broadening indicate an onset of clustering of Gd3+ ions at &amp;gt; 1wt % doping levels.

Investigation of multicomponent silicate glasses by coupling WAXS and molecular dynamics

An innovative method coupling molecular dynamics (MD) and reverse Monte Carlo (RMC) analysis allowed us to fit the interaction potentials on the experimental structure factors of aluminoborosilicate glass compositions obtained by wide-angle X-ray diffraction spectrometry (WAXS). By calculating the structural factors and the partial radial distribution functions, the combination of RMC and MD directly identifies the pair potentials requiring optimization. We observed that a Coulomb potential alone is not enough to model a sufficiently ordered local environment around the Na and Ca cations: additional terms were necessary to fit the repulsion and attraction terms. Analysis of the glass atomic structure revealed a larger number of F1–O–F2 groups in the glass containing CaO (where F i=Al or B ions), although the total number of these groups remains lower than would be expected from a random ion distribution. The relatively higher Ca coordination number around Al compared with B ions shows a preferential Ca–Al approach compared with Ca–B. Finally, analysis of the Na and Ca environments showed that the Na ions more readily act as pure charge compensators – i.e., distant from any non-bridging oxygen atoms – than do the Ca ions, most of which conserve non-bridging oxygen atoms in their local environment.

Crystallizing phases from multi-component silicate glasses in the system K 2O–CaO–MgO–Al 2O 3–SiO 2

The sequence of crystallization of phases in some glasses based on anorthite–diopside–forsterite containing 10–40% (wt.%) K-feldspar was studied. Phase association, transformation and extent of solid solutions development have been followed by X-ray diffraction, polarizing microscope; indentation micro-hardness was also measured. Diopside and anorthite were the primary crystalline phases and small amounts of microcline in K-feldspar-poor glasses. With increasing soaking time and temperature of heat-treatment, forsterite was developed meanwhile microcline was transformed into orthoclase. With an increase of K-feldspar to 40%, the anorthite phase disappeared and forsterite was transformed into enstatite while sluggish transformations of microcline into orthoclase were observed. The sequence of crystallizing phases is found to be as follows: diopside, anorthite, forsterite, microcline, then the orthoclase.

An Increase in the Refractive Index of a Multicomponent Silicate Glass by Six-Hundredths upon the Na+glass–Li+meltIon Exchange

An increase in the refractive index of the glass surface by Δn= 0.06 after the Na+glass–Li+meltion exchange is obtained for the first time.

Cationic ordering in oxide glasses: the example of transition elements

AbstractStructural data have been obtained on the cation surroundings in multi-component silicate and borosilicate glasses using chemically selective spectroscopic and scattering methods, such as extended X-ray absorption and neutron scattering with isotope substitution (NSIS). Transition elements such as Ni or Ti may occur in unusual 5-coordinated sites which coexist with other coordination numbers, depending on glass composition. Distribution of cationic sites in the glassy structure is responsible for unusual spectroscopic properties, as shown by Fe2+ Mössbauer spectroscopy. The environment of cations such as Zn, Zr or Mo, has been determined by EXAFS and discussed using the bond valence theory, which predicts the way to charge compensate the oxygen neighbours and which indicates the linkage of cationic sites with the silicate framework. Cation-cation correlations are given by NSIS up to ∼8 Á, indicating an extensive Medium Range Ordering (MRO) with corner- and edge-linked cationic polyhedra, for Ti and Ni-bearing glasses, respectively. This heterogeneous cationic distribution in glasses is consistent with the presence of two-dimensional domains in which cation mixing may occur, as shown in a Ca-Ni metasilicate glass. Three-dimensional domains have also been found by Ni-K edge EXAFS in the case of low alkali borate glasses, with a local structure which mimics some aspects of crystalline NiO. The presence of ordered cationic domains, clearly illustrated by Reverse Monte Carlo simulations helps to rationalize the physical properties of multi-component silicate glasses.

Nonlinear light absorption and luminescence in silicate glasses

The study of luminescence of high-purity multicomponent silicate glasses excited by radiation of a N2 laser (λ=337 nm, P≈12kW) showed darkening of a sample and a monotone decrease in luminescence intensity and the transmitted radiation intensity from pulse to pulse. Additional illumination with radiation of an Ar+ laser (λ=514.5 nm) caused an increase in luminescence intensity. An increase in absorption and a decrease in luminescence intensity were found to be caused by two-photon absorption and electron-hole pair production.

Some effects of γ-irradiation in soda-lime silicate glasses

Nanosized metallic silver particles have been formed in multicomponent commercial soda-lime silicate glasses partly substituted with ionic silver and irradiated at room temperature by γ-rays from a 60Co-source (1.33 MeV). To characterize the obtained composites, combined measurements of thermally stimulated depolarization current and optical absorption, accompanied by microspectrophotometric analysis and electron microscopy observations have been used. It has been shown that γ-irradiation might be an effective means to modify and control the concentration, size and spatial distribution of the dopant within the near-surface layer of the glass-matrix. This procedure also allows the conversion of some glassy areas in this region into a partially crystalline material with improved mechanical characteristics.

Photoionization of silicate glasses exposed to IR femtosecond pulses

Photoionization of alkali-silicate, boro-silicate, lead-silicate and photosensitive multi-component silicate glasses has been studied under exposure to infrared femtosecond laser pulses at irradiance below the thresholds of laser-induced damage and catastrophic self-focusing. It is proved that the supercontinuum that is generated in all glasses studied as a result of the femtosecond laser pulses spectral broadening extends up to the short-wavelength part of the ultraviolet region of spectrum even if the glass is opaque in this region. It is shown that photoionization results from absorption of the short-wavelength component of this supercontinuum generated by infrared radiation. This ionization leads to the color center formation and luminescence in the bulk of glasses studied. Photoionization of photosensitive multi-component glasses leads to the creation of latent image and to the refractive index changing in exposed area after thermodevelopment. Fused silica exhibits the same spectral broadening too but color center formation in the visible was not recorded at irradiance up to the laser damage threshold.

Er3+-doped multicomponent silicate glass planar waveguides prepared by sol-gel processing

Erbium doped silica-titania planar waveguides, co-doped with ytterbium and aluminum, have been prepared by sol-gel processing, using multilayer spin-coating deposition on silicon or silica glass substrates. The Er3+ doping level varied between 0 and 2 at.%, while Yb3+ varied from 0 to 3 at.%. Aluminum was incorporated up to 15 at.% Al and it was found to have no significant effect on the refractive index of the silica-titania (80 : 20 mol%) matrix. The Er3+ fluorescence emission was flat within ±0.5 dB, between 1520 and 1560 nm. The corresponding 4I13/2 metastable level lifetime was found to decrease from 6.1 to 3.5 ms, as the Er concentration increased from 0.1 to 0.5 at.%, for films co-doped with 0.5 at.% Yb and 10 at.% Al and the fluorescence decay was essentially single exponential below a Er quenching concentration of 0.5 at.% (1.1 × 1020 ions/cm3). The lifetime appears to be limited by Er-Er interactions at higher rare-earth ion concentrations and by residual OH species in the sol-gel derived waveguides. Vacuum heat treatment at a temperature near 570°C was somewhat effective in increasing the Er fluorescence lifetime, whereas reactive atmosphere processing in CCl4 or Cl2 at a similar temperature appeared to be less effective.

Local structure of Er 3+ in multicomponent glasses

Erbium environments in several multicomponent glasses are investigated using X-ray absorption fine structure spectroscopy on the Er L III-edge. Glass hosts studied include aluminosilicate, fluorosilicate, phosphosilicate, alkali phosphate, fluoride, and another multicomponent silicate glass. The Er–O separation is found to vary only slightly between 2.21 and 2.25 Å. The first shell coordination number is dependent on glass host ranging from 6.3 nearest neighbor anions in the aluminosilicate glass to 10.0 in the fluoride host. The Debye–Waller factor for the first shell is also host dependent. It ranges from 0.021Å 2 in the phosphate hosts to 0.033 Å 2 in the aluminosilicate glass. While Er–Er correlations are observed in the crystalline Er 2O 3 standard, no evidence of molecular or short-range clustering of Er 3+ ions is found in the glasses. Photoluminescence spectra are also presented for each of the glass hosts examined.