On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba₂CaMgAlF₁₄ were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N⁺, O⁺, Ar⁺ and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 10¹⁶ ions/cm². It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with g_z = 2.016, g_y = 2.009; g_x = 2.001 (FA₁) and g_z = 2.045; g_y = 2.010; g_x = 1.98 (FA₂) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and ΔH = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA₁- and FA₂-spectra are attributed to molecular 0₂⁻-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O₂O⁻, 0₄⁻ , CO⁺, CO⁻) located in voids of damaged implantation layer.     

Spatial and temporal observation of energy transfer processes in Pr-doped phosphate glasses

A spatially resolved microluminescence technique was used to measure the spatial distribution of emitted light and photon propagation into two different Pr³⁺ doped phosphate glasses. The photon diffusion length for specific wavelengths was measured. It was found that excited state re-absorption plays a crucial role in the propagation. Our results suggest that this microluminescence technique can be applied in the investigation of energy transfer processes in rare-earth doped systems.     

Orange and IR to violet up-conversion processes in Nd:ZBLAN glasses

In this work we investigate, compare and discuss UV and violet emission behaviour under pulsed, multi-photon orange and infra-red excitation in Nd³⁺ doped ZBLAN samples of different concentrations ranging from 0.3 to 5 mol.%. Supported by the obtained spectroscopic results, orange and IR excitation schemes were proposed and verified by time dependent rate equation model, which has been employed to confirm the nature of observed processes. Proposed model returns fitting results which qualitatively reflect the experimentally obtained fluorescence decays.     

Ac conductivity relaxation processes and its scaling behavior in sodium bismuthate glasses

Ac conductivity measurements and its analysis has been performed on the glassy ionic conductingx Na₂O + (1 –x) Bi₂O₃ system in the frequency range from 20 Hz to 1 MHz and in the temperature range 450 K to 750 K. The composition dependence of the dc electrical conductivity and activation energy has been obtained. The electrical relaxation analysis has been inquired on these glasses with universal power law and the random free energy barrier model. The relaxation parameters are obtained from the analysis has been compared. All experimentally known features of the () including its scaling behavior are explained satisfactorily. The results show an excellent agreement of scaling behavior based on random free energy barrier model and universal power law.     

Irradiation-induced gold silicide formation and stoichiometry effects in ion beam-mixed layer

The irradiation-induced silicide formation in ion beam-mixed layer of Au/Si(1 0 0) system was investigated by using 200 keV Kr⁺ and 350 keV Xe⁺ ions to fluences ranging from 8×10¹⁴ to 1×10¹⁶ ions/cm² at room temperature. The thickness of Au layer evaporated on Si substrate was ∼500 Å. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the irradiation effects on the mixed layers. We observed that at the fluence of 1×10¹⁶ Kr⁺/cm² and starting from the fluence of 8×10¹⁴ Xe⁺/cm², a total mixing of the deposited Au layer with Si was obtained. RBS data corresponding to the fluences of 1×10¹⁶ Kr⁺/cm² and 8×10¹⁴ Xe⁺/cm² clearly showed mixed layers with homogenous concentrations of Au and Si atoms which can be attributed to gold silicides.The samples irradiated to fluences of 1×10¹⁶ Kr⁺/cm² and 1×10¹⁶ Xe⁺/cm² were also analyzed by X-ray photoelectron spectroscopy (XPS). The observed chemical shift of Au 4f and Si 2p lines confirmed the formation of gold silicides at the surface of the mixed layers. Au₂Si phase is obtained with Kr⁺ irradiation whereas the formed phase with Xe⁺ ions is more enriched in Si atoms.     

Fluorescence properties and relaxation processes of Tb3+ ions in ZnCl2-based glasses

60ZnCl₂–20KCl–20BaCl₂–xTbCl₃ glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb³⁺ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the ⁵D₃ to ⁵D₄ level of Tb³⁺ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl₂-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (⁵D₃ → ⁵D₄) → (⁷F₀ ← ⁷F₆), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the ⁵D₃ → ⁷F_J (J = 6, 5, 4, 3, and 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the ⁵D₃ and ⁵D₄ initial levels were obtained to be 1.1 and 2.1 ms, respectively.     

Energy transfer processes in (Er3+–Yb3+)-codoped germanate glasses for mid-infrared and up-conversion applications

Luminescence characteristics of Er³⁺-activated, Yb³⁺-sensitised GeO₂–Na₂O–Nb₂O₅ heavy metal germanate glasses have been investigated in the context of searching active media for laser devices. Optical absorption, emission spectra and decay time measurements have been performed at room temperature on these materials. Intense 1540 nm infrared fluorescence and visible emission bands at 533, 554, and 660 nm were observed under continuous wave excitation at 980 nm.An efficient energy transfer from Yb³⁺ to Er³⁺ ions, increasing as a function of Yb³⁺ concentration, favours the Er³⁺ 1.54 μm eye-safe laser emission in these materials.The power dependence study of the upconverted emissions gives evidence of a bi-photonic process. Moreover, the Yb³⁺ codoping enhances the up-conversion efficiency. Decay time measurements have been examined in the purpose of elucidating the possible mechanisms involved in this process.The experimental results are in good agreement with an effective Yb³⁺-to-Er³⁺ nonradiative energy transfer.     

Lead in glasses

A literature review is given on the structure, crystallization and properties of lead glasses.     

Self-organization and rigidity in network glasses

Rigidity theory has helped in our understanding of the properties of network glasses. We analyze the connection between rigidity and various non-random features in the network structure. Lack of small rings in the network can lead to a sharper rigidity transition. We review a model of network self-organization that we have proposed, in which the existence of an intermediate phase that is rigid, but stress-free, is predicted. Finally, we discuss recent experiments, in which this intermediate phase may have been observed.     

Superflow and dissipation in porous glasses

The study of superflow of ⁴ He in proous vycor glass has a long venerable history, dating back to the early days of superfluidity. In this work we wish to address a number of outstanding questions. In doing so we have used a low frequency (250 Hz) Helmoholtz oscillator technique which uses filled pores and allows measurements to be made on small samples under a variable pressure gradient and at any temperature - not only below the superfluid transition (a feature also of torsional oscillator ¹ and acoustic techniques². An introduction to the resonator has already been published ³ . The techique has also been used to investigate aerogel porous glass ¹¹ but the main emphasis of this report will be on vycor.     

Optical piston in glasses

Abstract

Light-driven electron transitions between different traps in the direction opposite to an electric force eE (e is the electron charge and E is the static electric field) are studied. We show that in Ge-doped silica fibres the electrons are transfered predominantly between different Ge centres at concentrations ≥ 10 mol.% and dominate over the ordinary electron mobility in the direction of the force eE. Light acts as an optical piston, moving electrons against the acting force and therefore resulting in positive feedback in response to static electric field. This feedback amplifies the weak initial electric field up to magnitudes of the order of 10⁵?10⁶ Vcm^?1. This strong field breaks the initial inversion symmetry and allows effective second harmonic generation.     

Diffusion in metallic glasses

Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated. It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.     

Mechanical relaxation in glasses

The basic properties of glasses and the characteristics of mechanical relaxation in glasses were briefly reviewed, and then our studies concerned were presented. Experimental methods adopted were viscosity, internal friction, ultrasonic attenuation, and Brillouin scattering measurements. The specimens used were several kinds of inorganic, organic, and metallic glasses. The measurements were mainly carried out from the room temperature up to the glass transition temperature, and the relaxation time was determined as a function of temperature. The “double relaxation” composed of two Arrhenius-type relaxations was observed in many materials. In both relaxations, the “compensation effect” showing a correlation of the pre-exponential factor and the activation energy was observed. These results were explained by considering the “complex relaxation” due to cooperative motions of atoms or group of atoms. Values of activation energy near the glass transition determined by the various experimental methods were compared with each other.