Role of Cerium in Suppression of Gamma-Ray Induced Coloring of Borate Glasses

The role of cerium in the suppression of gamma-ray induced coloration in glass has been found to depend on the relative concentration of Ce³⁺ to Ce⁴⁺ ions as well as on the total cerium content. In a borate glass having high ultraviolet transmission, it has been found that both Ce³⁺ and Ce⁴⁺ ions are necessary to suppress the optical absorption bands induced in the visible region. The role of cerium can be explained on the basis of a change in its oxidation state as a result of gamma irradiation. It is postulated that the cerous ions, by the reaction Ce³⁺→ Ce⁴⁺+ e , suppress the induced visible band at 2.36 ev (525 mμ), which may result from positive hole centers. High cerous ion concentration results, however, in an induced center (Ce³⁺+ e ) which absorbs in the visible at about 1.9 ev (650 mμ). The presence of Ce⁴⁺ ions near Ce³⁺ prevents the formation of this center possibly by the reaction Ce⁴⁺+ e → Ce³⁺. These induced opposite changes in the oxidation state of cerium tend to maintain a balance in the ratio of Ce³⁺ to Ce⁴⁺ ions in the glass during irradiation, and the suppression of the visible bands depends on this ratio.     

Gamma-Induced Absorption Bands Associated with Tl+, Pb2+, or Bi3+ in Potassium Borate Glasses

Gamma irradiation of potassium borate glasses containing about 1.8 mole % Tl⁺, Pb²⁺, or Bi³⁺ resulted in two induced absorption bands which the authors call T and L bands. The T band was observed at about 1.1, 1.55, or 1.8 ev, and the L band was observed at about 1.8, 2.6, or 2.7 ev in alkali borate glasses containing Tl⁺, Pb²⁺, or Bi³⁺, respectively. The shifting of the band positions to higher energies was attributed to the increasing polarizing power of these ions as in the case of the F band induced in alkali halides. The effect of the addition of cerium on the intensity of the T and L bands induced in glasses containing lead or thallium and prepared under different melting conditions suggested strongly that these two bands are associated with electron trap centers near these ions.     

Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was x PbO (100 − (x + y) )BiO_1.5. yGaO_1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO_1.5 and decreased with increased PbO or BiO_1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga^{3 +} ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi³⁺ and Pb²⁺ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb⁴⁺. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.     

Effect of Composition on Glass-Metal Interface Reactions and Adherence

Reduction-oxidation reactions and enhanced wetting or spreading of Na₂Fe_xSi₂O_5+x, and Na₂Ni_xSi₂O_5+x glasses on substrates of Fe, Co, Ni, Ni-Fe, and Ni-Co were observed at 1000°C at low partial pressures of O₂ and Na as the O/Si ratio of the glass increased. When the substrate had a higher oxidation potential than the metal of one of the cations in the glass, e.g. CoO-containing glass on Fe, metallic precipitates formed by redox reactions under all conditions. A redox reaction based on reduction of the valence of a cation in the glass, e.g. Fe³⁺ to Fe²⁺, also occurred. Adherence developed between substrates and glasses containing amounts of substrate oxide, either in the starting composition or formed by redox reactions, approaching saturation.     

Composition Effects on Optical Properties of Tb3+-Doped Heavy Germanate Glasses

A group of terbium-doped heavy germanate glasses were studied. Glass matrices contained GeO₂, Gd₂O₃, BaO, and/or La₂O₃ with the Tb³⁺ doping concentration ranging from 1 to 5 mol%. The transmission and radioluminescence spectra were measured and their correlations with glass composition are discussed. It is found that the UV cut-off edge of glass matrices is related to the content of the network modifier BaO as well as to the mixed rare earths effect, while the concentration of trapping sites existing in the glass network is essential to the radioluminescence properties of the glass. The latter is also associated with the content of the network modifier BaO that produces unsaturated nonbridging oxygens in the glass lattice. Another important mechanism influencing the luminescence process involves the enhanced energy transfer from Gd³⁺ ions to Tb³⁺ emission centers. A self-sensitizing effect of Tb³⁺ is observed in the Tb³⁺ concentration range studied, which contributes to some extent to the enhanced Tb³⁺ green emission. La₂O₃ additions to the host glass play an active role of partitioning Tb³⁺ in the glass matrix, thereby showing an enhanced blue emission because of the reduced cross-relaxation probability between Tb³⁺ cations.     

Point Defects and Chromium(IV) Formation Mechanism in Gallia- and Alumina-Based Oxide Glasses

Point defects were found in as-quenched GeO₂, 65CaO35Al₂O₃, and 65SrO35Ga₂O₃ glasses on the basis of electron paramagnetic resonance (EPR) measurements. These defects were identified as Ge É centers in GeO₂ glass and O^-₂, O^-₃, and M-OHC (oxygen hole center) (where M = Al, Ga) in 65CaO35Al₂O₃ and 65SrO35Ga₂O₃ glasses. The formation of Ge É centers in as-quenched GeO₂ glass was due to the thermodynamic stability of GeO at the melting temperature. The latter oxygen-excess defects are supposed to be formed by excess oxygen ions derived from the modifiers in the aluminate and gallate glasses during the formation of these glasses. To investigate some of the properties of the oxygen-excess defects in the calcium aluminate and strontium gallate glasses, chromium ions were doped in these glasses as a probe and the relationship between the valency state of the chromium ion and the defects was determined. We conclude that the peroxy bonding (-O-O-) oxidizes the Cr³⁺ species to Cr⁴⁺. Similar defects have been identified in host compounds that are used for Cr⁴⁺ tunable lasers. These results reveal that the point defects are necessary to stabilize the Cr⁴⁺ ions in glasses and crystals.     

Interaction of Gamma Rays with Calcium Aluminoborate Glasses Containing Holmium or Erbium

The optical absorption spectra of nominally pure and rare-earth-ion-doped (Ho³⁺ or Er³⁺) calcium aluminoborate (cabal) glasses were measured from 190 to 900 nm before and after γ-ray irradiation. The induced absorption spectra, calculated as the difference between the spectra of the irradiated and the unirradiated glasses, exhibit the characteristic absorption bands caused by the respective rare-earth ions. The intensity of the induced bands depends on the rare-earth oxide content. The response of the cabal glass to γ-ray irradiation is related to the formation of color centers associated with the intrinsic defects in the lattice structure of the cabal glass. The rates of formation and annihilation of the color centers are believed to approach saturation or equilibrium with prolonged irradiation.     

Optical Absorption and Color Caused by Selected Cations in High-Density, Lead Silicate Glass

The effect of impurities on the color of dense flint glass was investigated by comparing the optical absorption caused by cations in Na₂O·3SiO₂·2PbO glass, in Na₂O·3SiO₂·2PbO:1 wt% Sb₂O₃ glass, and in Na₂O·3SiO₂ glass; all three are colorless when of high purity. Of 11 colorants, only vanadium colored both lead glasses less intensely than the Na₂O·3SiO₂ glass. Factors that make the lead glass more susceptible to coloration are higher oxidation states of polyvalent cations, larger absorption cross sections of polyvalent cations, and the tendency of prominent absorption bands to be closer to the wavelength at which eye sensitivity is a maximum.     

Gamma-Ray Induced Coloring of Some Phosphate Glasses

The changes in gamma-ray induced optical absorption in phosphate glasses resulting from changes in composition, conditions during melting, and additions of small amounts of some oxides are discussed. A resolution of the induced spectra showed that the observed absorption is due to the superposition of three bands at 2.3, 2.9, and 5.5 e.v. (540, 425, and 225 mü) and to a fourth band whose absorption peak is beyond 6 e.v. The ultraviolet induced absorption increases, whereas the visible absorption decreases in glasses melted under reducing conditions as opposed to those melted under normal conditions in air and on replacement of K⁺ by Na⁺ or Li⁺. A similar effect is produced on replacement of Ba⁺⁺ by Pb++ and on the addition of T1₂O to a CaO-P₂O₅ glass or the addition of As₂O₃ to a CaOP₂O₅, GeO₂ glass. Additions of large amounts of GeO₂ are accompanied by a decrease in the number of nonbridging oxygens and a decrease in the visible induced absorption. Replacement of Ca ⁺⁺ by Ba⁺⁺ ions showed an over-all decrease in the induced absorption. The addition of small amounts of the oxides of germanium, titanium, iron, thallium, niobium, and arsenic showed an appreciable effect in inhibiting the visible induced coloration.     

Reaction and Diffusion in Silver-Arsenic Chalcogenide Glass Systems

The diffusion of Ag from the metal or Ag₂Se in amorphous As₂S₃ and As₂Se₃ at 175°C is accompanied by the reduction of As from a valence of 3+ to 2+ or 2+ to 1 + to maintain charge neutrality in the glass. Only Ag⁺ diffuses at this temperature; all other ions are essentially immobile. An amorphous reaction-product phase is formed in the diffusion zone with a composition range of 28.6 to 44.4 at % Ag. The lower limit corresponds to all As cations of 2+ valence (equivalent to amorphous Ag₂As₂S₃); the upper limit, the maximum solubility of Ag in these glasses, corresponds to all As cations of 1 + valence (equivalent to amorphous Ag₁As₂S₃). The diffusivity of Ag in these glasses at 175°C for concentrations of 10 to 35 at.% Ag is
Sulfide 4× 10⁻¹⁴ exp[(+0.23±0.01)(at.% Ag)]cm²/s
Selenide 2' 10⁻¹¹ exp[(+0.14±0.01)(at.% Ag)]cm²/s     

Stannous-Stannic Equilibrium in Molten Binary Alkali Silicate and Ternary Silicate Glasses

The stannous-stannic equilibrium in binary alkali silicate and ternary silicate glasses was studied by equilibrating glassmelts with air at 1400°C. The Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the oxidized state with increasing ionic radii of the alkali ions or with increasing concentration of the alkali ions in the same series of glasses. The slope of the straight lines obtained on plotting log (Sn⁴⁺)/(Sn²⁺)( pO₂ )^n/2 vs mol% R₂O increased in the order Li→Na→K. In ternary silicate glasses having the base glass composition 20Na₂O·10RO·70SiO₂, the Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the reduced state, with increasing bond strength between the divalent cations and the nonbridging oxygens. With increasing temperature, the equilibrium shifts more toward the reduced state.     

Titanium Centers Induced in Borate Glasses by Irradiation

The electron paramagnetic resonance of alkali borate glasses containing Ti was observed at 9.1 GHz before and after room-temperature X irradiation. The irradiation-induced spectra can be separated into (1) the well-known complex borate resonance with an average g value greater than that of the free electron (2.0028) and (2) a resonance with a lower g value. The latter resonance consists of two asymmetric ESR lines, one broad and the other narrow, whose characteristics are reported. These lines were not observed in the corresponding Ti-free base glasses; they arise from induced Ti centers. The broad asymmetric line ( T ₁) corresponds to a Ti^3.1 ion in sixfold coordination, whereas the narrow asymmetric line ( T ₂) corresponds to a Ti³⁺ ion in a different structural configuration. Lines T ₁ and T ₂ are stable at room temperature, not easily saturated with microwave power, and exhibit behavior independent of the complex borate resonance. The total relative intensity of these lines depends on the total Ti concentration in the glass, the Ti⁴⁺/Ti³⁺ ratio in the glass before irradiation, and the structure of the glass.     

Electrical Resistivity of Titanium-Containing Glasses

Titanium-containing glasses were prepared by fusion of a base glass (BaO·B₂O₃SiO₂) and TiO₂ and/or Ti₂O₃ in Ar. Their resistivities did not vary with melting time and temperature. Interaction of Ti⁴⁺ and Ti³⁺ in the glasses was deduced by spectroscopy, but the valence states in the batch compositions were preserved in the glasses, according to the chemical analysis. Glasses containing either Ti⁴⁺ or Ti³⁺ had very high resistivities, whereas the glass prepared by melting a mixture of a Ti⁴⁺-containing and a Ti³⁺-containing glass had much lower resistivity. All results confirmed the possibility of controlling the resistivity by batch composition for these glasses.     

Infrared, Raman, and Electron Spin Resonance Studies of Vitreous Alkaline Tungsten Phosphates and Related Glasses

Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P₂O₅–WO₃–A₂O (A = Li, Na). Structural approach of the highly modified glasses P₂O₅–A₂MoO₄–A₂O (M = Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO₆octahedra, MO₄tetrahedra, M₂O₇dimers, PO₄tetrahedra, and also P₂O₇or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A₂O increases. ESR experiments were conducted on both X-ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W⁵⁺ and Mo⁵⁺ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus–oxygen–hole–center and peroxy radicals. The M⁵⁺ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted for vitreous materials.     

Effect of Corrosion Processes on Subcritical Crack Growth in Glass

Crack-growth studies were conducted on soda-lime-silica, soda borosilicate, and two binary soda-silica glasses immersed in solutions of 1 M Li⁺, 1 M Cs⁺, or deionized water at different pH values. A definite effect of the Li⁺ and Cs⁺ was observed on the V-K₁ curves in all but the soda-lime glass. A plateau in crack velocity in the range 10-⁸ to 10-¹⁰ m/s was measured on the binary soda-silica glasses for K₁<0.35 MPa.m^1/2. These data are analyzed in terms of both the ion exchange and SiO₂ dissolution steps of the corrosion process. A model of crack growth in corrosive conditions is proposed.     

Composition Induced Reducing Effects on Eu Ions in Borophosphate Glasses

Europium-doped borophosphate glasses were prepared by the melt quenching method for application in light-emitting diodes. Emission spectra and electron paramagnetic resonance were studied for the glass samples. The relative intensity ratio of Eu²⁺ to Eu³⁺ emissions is composition dependent, especially the B₂O₃/P₂O₅ (B/P) ratio and the type of alkaline earth cations. The possible mechanisms are discussed.     

Reduction of Eu3+ to Eu2+ in Aluminoborosilicate Glasses Prepared in Air

Eu₂O₃-doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu³⁺ to Eu²⁺ ions in the aluminoborosilicate glasses. The results showed that the doped Eu³⁺ ions were partially reduced to Eu²⁺ in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=CaO, SrO, BaO, Li₂O) glasses, but not in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=Na₂O, K₂O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed.     

Generation of Emission Centers for Broadband NIR Luminescence in Bismuthate Glass by Femtosecond Laser Irradiation

Bismuth-doped glasses have recently received significant interest as potential material for ultrabroadband optical amplification in the telecommunication spectral bands, as well as as gain material for fiber lasers. However, the nature of the active centers that are responsible for the observed near-infrared (NIR) luminescence is still highly debated. In order to probe the mechanism that leads to NIR emission in bismuth-containing glasses, femtosecond (fs) laser irradiation was used. It is shown that local absorption properties in the visible spectral range can be altered in initially transparent bismuthate glasses after fs laser irradiation. Induced absorption centers exhibit the well-known broadband optical emission peaking at ∼1250 nm when excited with a 785 nm diode laser. Absorption and emission intensities increase with increasing average pulse energy. These observations are interpreted as a photo-induced reduction reaction of Bi³⁺ to Bi⁺ species, while the previously discussed formation of Bi-clusters by ion diffusion is excluded due to the very short interaction time that results from the use of fs laser. Bi⁺ species are, therefore, proposed as the major origin of NIR emission from Bi-doped glasses.     

Electrical Properties of Nonconventional Bi-Ba-Cu-O Glasses

Electrical properties of Bi-Ba-Cu-O glasses have been systematically investigated, and possible conduction mechanisms are discussed. Conductivity behavior is described by a small-polaron hopping mechanism. log σ_o, the slope of the log σ- W straight line, and the magnitude of the polaron bandwidth reveal that adiabatic hopping is dominant in the glasses. The Seebeck coefficient, S , of the Bi₁₆BaCu₃O_y glass is positive, indicating that the glass is a p -type hole conductor. The positive deviation of the observed S value from the theoretical S value is explained by assuming that the only oxygens bonded to both Cu²⁺ and Cu⁺ ions mediate indirect Cu⁺-O-Cu²⁺ hopping.     

Compositional Dependence of Absorption Spectra of Ti3+ in Silicate, Borate, and Phosphate Glasses

Absorption spectra of Ti³⁺ were measured for silicate, borate, and phosphate glasses doped with 0.5 mol% Ti₂O₃.The absorption coefficient at the peak wavelength of the ₂T₂→₂E transition of Ti³⁺ is used as a parameter showing the relative content of Ti³⁺ions in glass samples. The effect of glass composition on Ti³⁺/Ti⁴⁺ redox was studied. For multicomponent glasses, a basicity parameter calculated from glass composition is proposed in terms of coulomb force between the cation and the oxygen ion. The value of the absorption coefficient depends on basicity in silicate and borate glasses; however, it is independent of composition in phosphate glasses.