Calculation of thermal expansion coefficient of glasses

Thermal expansion of oxide glasses has been theoretically studied to derive an equation for the calculation of the thermal expansion coefficient of glass from chemical composition. Grüneisen's constant may be correlated with packing density and a ratio of cation-to-anion radius and, considering the packing density and dissociation energy per unit volume, a semi emprical equation was derived. The agreement between observed and calculated values was satisfactory over 150 glasses of the binary, ternary and quarternary systems.     

Microheterogeneities in infrared optical selenide glasses

Flocculent inhomogeneities in vitreous Ge₂Se₃ were identified as being SiO₂. The origin of these particles was found in the walls of the vitreous silica tubes in which the glass was prepared. By etching or thermal treatment of the tubes prior to their use the concentration of the microheterogeneities in the selenide glass can be considerably reduced. This is also valid for the preparation of glasses of the system GeAsSe and GeSbSe.     

DC electronic transport in binary arsenic chalcogenide glasses

dc conductivity and Seebeck measurements have been carried out at temperatures below T_g on well characterized bulk samples of amorphous As₂Te₃, As₂Se₃, and As₂S₃. Several models for conduction in these materials have been compared to the data. It is concluded that the models involving polaron hopping conduction are in better agreement with available data than are models involving hopping in the tails of localized band-tail states.     

Temperature dependence of dielectric losses in chalcogenide glasses

The frequency (2 × 10⁴?2 × 10⁷ Hz) and temperature (250–600 K) dependence of the imaginary part of the permittivity, ?′', of As₂Se₃ and Tl₂SnSe_8.61 is explained within a theoretical model. The dielectric premittivities of these compounds are correctly explained by means of a model of a hopping process over a potential barrier between localized sites.We have found that the glassy system of chalcogenide can exist in the form of dipoles. The theory shows, in agreement with the experimental results, that ?′' = Aω^m, where m is a function of temperature.     

Structural and optical properties in gadolinium-aluminum-lead-germanate quaternary glasses

Glasses in the quaternary system 0.05Al₂O₃·0.95[xGd₂O₃·(100-x)(7GeO₂·3PbO)] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. In this paper, we investigated structural and optical properties in gadolinium-alumino-lead-germanate glasses through investigations of FTIR (Fourier-Transform Infrared Spectroscopy) and UV-VIS (Ultra-Violet) spectroscopy.The observations presented in these mechanisms show that by increasing Gd₂O₃ content up to 40 mol%, the glass network modification has taken place mainly in the germanate part, while the excess of oxygen can be accommodated in the host network by the creation of shorter rings of [Ge₂O₇] structural units and the formation of [AlO₄] structural units. The affinity pronounced of the gadolinium cations towards germanate structural units produces the formation of the Gd₂Ge₂O₇ crystalline phase.The UV-VIS spectroscopy data show the charge transfer transitions of Pb^+ 2-O^− 2, Al^+ 3-O^− 2 and Gd^+ 3-O^− 2, respectively. The additional absorption in the range of 300 to 600 nm was attributed to other types of defects such as: non-bridging oxygen ions, change in valency of ions and other color centers.The values of the direct optical band gap of the glasses are determined from the optical absorption spectra. By increasing Gd₂O₃ content in the glass matrix, the optical band gap energy increases indicating changes of the lattice parameters by Gd₂O₃ incorporation.     

Light scattering in a number of optical grade glasses

Light scattering measurements have been made on a number of commercially available optical grade glasses. By measuring the spectrum as well as intensity of the scattered light it was found possible both to obtain the total scattered intensity and to identify the origin of the scattering. The optical attenuation coefficient due to scattering was evaluated. It was found that in all glasses studied the total scattered intensity exceeds that in fused silica by at least a factor of two.     

Relationship between refractive index,optical electronegativities and electronic polarizability in alkali halides,III–V,II–VI group semiconductors

Refractive indices have been evaluated from DUFFY'S optical electronegativities. The validity of the proposed empirical relation has been tested in the case of II–Vi, III–V compound semiconductors and alkali halides by comparing the calculated values of n with those in the literature. The estimated refractive indices are used in Classius-Mossotti relation to evaluate electronic polarizabilities in the above compounds. The nature of the bonding in terms of Δχ and n is discussed. Good agreement is observed between the computed and literature values of electronic polarizability.     

Novel Bi-doped glasses for broadband optical amplification

Broadband infrared luminescence is observed in various Bi-doped oxide glasses prepared by conventional melting-quenching technique. The absorption spectrum of the Bi-doped germanium oxide glass consists of five broad peaks at below 370, 500, 700, 800 and 1000 nm. The fluorescence spectrum exhibits a broad peak at about 1300 nm with full width at half maximum (FWHM) of more than 300 nm when excited by an 808 nm laser diode. The fluorescence lifetime at room temperature decreases with increasing Bi₂O₃ concentration. Influence of the glass composition and melting atmosphere on the fluorescence lifetime and luminescent intensity is investigated. The mechanism of the broadband infrared luminescence is suggested. The product of stimulated emission cross-section and lifetime of the Bi-doped aluminophosphate glass is about 5.0 × 10^?24 cm² s. The glasses might be promising for applications in broadband optical fiber amplifiers and tunable lasers.     

Temperature evolution of copper oxide nanoparticles in porous glasses

The temperature evolution of copper oxide nanoparticles in the temperature range of 1.5–250 K has been investigated by thermal-neutron diffraction. CuO particles were obtained by Cu(NO₃)₂ · 3H₂O decomposition directly in the pores of porous glass with an average pore diameter of 7 nm. The characteristic nanoparticle size and linear thermal expansion coefficients have been determined.     

A reversible optical transition in Se---Ge and P---Se---Ge glasses

A reversible optical transition has been found in thin films of Se---Ge and P---Se---Ge glasses. This optical transition is similar to that found in As---Se---Ge and As---Se---S---Ge glass films; heating causes the shift of the absorption edge to shorter wavelengths, and illumination moves it to longer wavelengths without crystallization. It was found that the presence of arsenic is not always necessary. Fundamental optical properties of these glasses, i.e. absorption constant, optical energy gap, change of the optical energy gap, and the refractive index by heating and illumination are reported. Change of the optical energy gap and the refractive index is small in Se---Ge and P---Se---Ge glasses, compared with that in As---Se---Ge and As---Se---S---Ge glasses.     

Structural and optical properties of the gadolinium-lead-germanate glasses

Glasses in the system xGd₂O₃(100 − x)[7GeO₂·3PbO] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. The influence of gadolinium ions on structural behavior in lead-germanate glasses has been investigated using FTIR, UV-VIS and EPR spectroscopy. The structural changes have been analyzed with increasing rare earth concentration.FTIR data suggest that the glass network modifications has taken place mainly in the germanate part whereas the lead part remained unmodified and its network consists mainly from the [GeO₄], [GeO₆], [Ge₂O₇] structural units and with interconnected through Ge-O-Ge bridges in [GeO₄] structural units. The changes in amplitude and bandwidth of the UV-VIS bands ranging from 200 nm to 350 nm depend on the content of Gd₂O₃.By increasing the Gd₂O₃ content in the glass matrix, the optical band gap energy increases, indicating changes of the lattice parameters and that no non-bridging-oxygens form upon the addition of gadolinium oxide. The decreasing trend has been observed both in optical gap band energy and refractive index of oxide glasses at x = 10 mol% Gd₂O₃ indicating breaks up the [GeO₄] tetrahedral units bonds and create of non-bridging oxygen atoms. For sample with x ≥ 20 mol%, the gadolinium ions having a behavior of network formers (g ≈ 4.8) will coordinate more with the excess of oxygen. Accordingly, the gadolinium ions are generally suspected to improve their environment of network formers.     

ESR and optical absorption of cupric ion in borate glasses

ESR and optical absorption of Cu²⁺ were measured in xNa₂O(100?x)B₂O₃ (1 ≤ x ≤ 75), x ZnO(100?x)B₂O₃ (46 ≤ x ≤ 64) and x Pb(100?x)b₂O₃ (20 ≤ x ≤ 75) glasses, where x is expressed in mol.%. Spin hamiltonian parameters and ligand field absorption energy changed abruptly in the regions of 15 ≤ x ≤ 23 and 37 ≤ x ≤ 55 in the soda system, while both parameters were hardly dependent upon the glass composition in zinc and lead systems. The magnitude of micro-environmental fluctuation of Cu²⁺-complexes in the glasses was estimated qualitatively and correlated with the distribution of the strength of π-bonding between cupric ion and oxygen in the glass. Typical network modifiers and intermediates behaved differently, especially in the composition region of invert glass; the large deformation of the coordination sphere of Cu²⁺ in lead glasses due to the stronger PbO bond resulted in the large distribution of $\text{g}{}_{\mathrm{}}$. The situation was reverse in the case of soda glasses.     

Characterization of the reversible photoinduced optical changes in Sb-based glasses

Changes occurring in absorption coefficients when glasses in the SbPO₄–WO₃ binary system were irradiated by light, at the edge of the absorption band, were measured in real time. These glasses present good thermal and optical properties and photoinduced changes in the absorption coefficients are reversible by heat treatment around 150 °C. Subsequent recording/erasing cycles could be made without sample degradation. The sensitivity of the induced optical changes was studied for different wavelengths, light powers and energy of light dose exposures, and for different compositions of the glasses. The changes in the absorption coefficients of the glass samples were accompanied by a color change from yellow to blue, and were also characterized by visible spectroscopy. The color changes occurred through the entire volume of the glass (∼2 mm thickness) for the Ar-ion laser lines at the edge of the absorption band.     

Studies of the optical properties of sodium copolyphosphate glasses

A number of samples of glassy sodium polyphosphate and copolyphosphates of sodium — cobalt, sodium — copper, sodium — nickel, sodium-manganese and sodium — calcium were prepared and their optical properties were investigated. The ultraviolet and visible spectra of these glasses were recorded at the room temperature. It was found that the fundamental absorption edge of these glasses usually occurs in the ultraviolet — visible region. The optical absorption edges (E₀) were calculated by using the relation h ν = B (hν − E₀)² where B is constant. The linear variation of (hν)^1/2 with hν where is the absorption coefficient and hν is the incident photon energy, is taken as evidence of non-direct interband transitions. The E₀ values obtained for copolyphosphate glasses appeared to depend on the size of the counter cation. The infrared spectra of all these glasses appeared to be almost the same, indicating the presence of characteristic P --- O --- P linkages of linear polyphosphate chains and two non bridging oxygen atoms bonded to phosphorus atoms O --- P --- O (PO₂) units in the polyphosphate tetrahedra.     

Sintering inhomogeneous glasses: Application to optical waveguides

Variations in viscosity or pore size within a glass body cause uneven contraction during sintering. Consequently, stresses develop which alter the local sintering rate and, in some cases, produce bulk flow. This paper illustrates how these stresses can be analyzed by analogy to thermal stress. As a particular example, sintering of optical waveguide preforms made by the OVPO process is examined in detail. The magnitude of the self-stresses, and the conditions required for bulk flow are determined.     

Temperature dependence of self-diffusion coefficient in several liquid metals

The temperature-dependent self-diffusion coefficient D(T) in liquid metals between the melting temperature T_m and boiling point T_b is modeled in terms of the relationship among D, liquid viscosity η, and liquid–vapor surface tension γ_lv. The model predictions for D(T) correspond to available experimental and molecular dynamics (MD) simulations results for liquid alkali metals Li, Na, Rb and Cs, semi-metal Al, transition and noble metals Ni, Cu, Ag and Au.     

Relaxation processes in glasses as shown by optical attenuation experiments

Some optical attenuation experiments on both bulk glasses and cladded glass fibres (fibre optics) are described. They reveal the presence of relaxation processes in the glass in its transformation range.