Gamma Irradiation Studies of Some Borate Glasses

The gamma-ray-induced optical absorption in a series of cabal (calcium-boron-aluminum) glasses was studied and is interpreted, wherever possible, in terms of structural concepts. A resolution of the observed absorption spectra showed that three Gaussian-shaped bands were induced with their maxima at about 2.3, 3.5, and 5.0 e.v. (550, 350, and 250 m_μ). The 2.3-e.v. band decreased in intensity with increasing CaO content, reaching a minimum intensity at a composition corresponding to the four-coordination of about 20% of the boron. Further increase in CaO content was associated with an increase in the intensity of this band. The intensity of the 3.5-e.v. band decreased gradually with increased mole per cent of CaO and increased with increased Al₂O₃. The 5.0-e.v. band showed an abrupt increase in intensity which corresponded to the appearance of non-bridging oxygens in the network. Replacing Ca²⁺ by Mg²⁺, Sr²⁺, or Ba²⁺ or replacing Li⁺ by Na⁺ or K⁺ showed that glasses containing large ions of low field strength give less induced absorption than glasses containing small ions of high field strength. A potassium alumina borate glass melted under reducing conditions gave a considerably higher ultraviolet transmission, before irradiation, as compared with the same glass melted under normal conditions. The gamma-induced absorption of these two glasses showed that reducing conditions resulted in a decrease in the intensity of the 2.3- and 3.5-e.v. bands, whereas it caused an increase in the far-ultraviolet-induced absorption. The effect of additions of arsenic, thallium, titanium, germanium, and some rare-earth oxides is discussed.     

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.     

Determination of OH Extinction Coefficients in R2O-B2O3-SiO2 Glasses (R = Li, Na, K)

Infrared spectra of glasses of the system R₂O-B₂O₃-SiO₂ were investigated. The extinction coefficients of the hydroxyl absorption band ("free OH") were calculated by a method proposed for alkali borate glasses. The results confirmed the applicability of this method to homogeneous and phase-separated alkali borosilicate glasses. The variation of the hydroxyl absorption band position was interpreted according to the structural characteristics of the studied glasses.     

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.     

Characteristics of PbO–BiO1.5–GaO1.5 Glasses Melted in SnO2 Crucibles

PbO-BiO_1.5-GaO_1.5-based glasses are good candidates for optical applications, because of some of their interesting characteristics, such as high refraction indices and high transmission in the ultraviolet (UV), visible (VIS), and infrared (IR) regions. A limited stage in the processing of these glasses is the corrosion that is caused by the melt in all currently used conventional crucibles, such as noble metals (platinum or gold) and Al₂O₃. The absorption of crucible material by the glass composition may reduce the transmission level, the cutoff in the UV-VIS, and IR regions, and the thermal stability. In this study, a SnO₂ crucible has been tested for PbO-BiO_1.5-GaO_1.5 molten glass. Optical and thermal analyses show, in some cases, advantages over the use of platinum and Al₂O₃ crucibles. A visible cutoff value of 474 nm has been measured, and a longer melting time (850°C for 4 h) results in a significant reduction of the O-H absorption band at 3.2 μm.     

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.     

Effects of Doping Trivalent Ions in Bismuth Borate Glasses

Bismuth borate glasses from the system: 40Bi₂O₃–59B₂O₃–1Tv₂O₃ (where Tv=Al, Y, Nd, Sm, and Eu) and three glasses of composition: 40Bi₂O₃–60B₂O₃, 37.5Bi₂O₃–62.5B₂O₃ and 38Bi₂O₃–60B₂O₃–2Al₂O₃ were prepared by melt quenching and characterized by density, UV-visible absorption spectroscopy and differential thermal analysis (DTA) studies. Bismuth borate glasses exhibit a very strong optical absorption band just below their absorption edge. Glasses were devitrified by heat treatment at temperatures above their glass transition temperatures and the crystalline phases produced in them were characterized by Fourier transform infrared (FTIR) absorption spectroscopy and X-ray diffraction (XRD). Bi₃B₅O₁₂ was found to be the most abundant phase in all devitrified samples. DTA studies on glasses and FTIR and XRD analysis on crystallized samples revealed that very small amounts of trivalent ion doping causes significant changes in the devitrification properties of bismuth borate glasses; rare-earth ions promote the formation of metastable BiBO₃–I and BiBO₃–II phases during glass crystallization.     

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.     

Effect of Fluorides on Infrared Transmittance of Certain Silicate Glasses

Relatively large amounts of fluorides can be incorporated into silicate glasses without producing opalescence or turbidity if certain oxides, such as La₂O₃ or Ta₂O₅, are included in the glass composition. In most cases, the fluorides reduce the absorption at the 2.75-μ water band, thus improving the glasses for use as infrared material. The fluorides also decrease the refractive index values of the glasses. Striae are produced in the glasses when the fluoride content is more than about 4 mole %.     

Visible Spectroscopy of Irradiated High-Alkali Borate and Mixed-Alkali Phosphate Glasses

Expectations of increased stability for trapped electrons in high-alkali glasses, based on extrapolations from observations on low-alkali borate glasses, are not borne out. In 69Na₂O-31B₂O₃ glass, electron centers have approximately the same thermal stability as in Na₂O·2B₂O₃ glass. In Na₂Oplus;P₂O₅ glasses the lifetimes, 3 · 0.5 μS, of transiently trapped electrons as well as their absorption spectra prove to be independent of increase of Na₂O content from 50 to 60 mol%. The same composition change destabilizes "permanent" hole centers. Exchange of Na₂O with K₂O in the metaphosphate glass also has no effect on the trapped electron lifetime. Small linear shifts in the trapped-hole absorption peak wavelengths are observed in the latter case. The most important positive finding in the phosphate glasses is a pronounced mixed-alkali effect on the yield of transiently trapped electrons and holes and of permanently trapped holes. The yield is a minimum at Na:K=1:1, due either to the elimination of trap sites or to the reduction of alkali ion mobilities which play a role in trap formation.     

Preparation and Properties of Heavy-Metal Fluoride Glasses Containing Ytterbium or Lutetium

Beginning with a 19BaF₂−27ZnF₂−27YbF₃−27ThF₄ (mol%) base glass, compositional modifications were made to improve optical properties and glass-forming ability. Replacement of YbF₃ by LuF₃ removed a strong near-ir electronic absorption band, and small additions of LiF and NaF improved glass quality. The multicomponent BaF₂/ThF₄ glasses had higher refractive indices and lower expansion coefficients than fluorozirconate and fluorohafnate glasses. In the 6 to 10 μm region, these materials exhibit absorption coefficients an order of magnitude lower than those reported for other heavy-metal fluoride glasses.     

States of Sulfur in Alkali Borate Glasses

Simple binary alkali borate glasses of differing alkali content (alkali = Li, Na, or K) containing sulfur were prepared and their absorption spectra were measured in the range of 200 to 700 nm. The absorption bands obtained were used to determine the stable states of sulfur in these glasses by directly comparing them with published data. The following states of sulfur were identified and their ranges of stability were determined: the S₂ molecule in glasses containing at least 15 mol% alkali oxide, the S₃⁻ and S₂⁻ in glasses containing 20 to 30 mol% Na₂O or K₂O, and the polysulfide ion (S x ²⁻) in glasses of 30 to 35 mol% Na₂O or K₂O.     

Infrared Spectroscopy of Wide Composition Range xNa2S + (1 –x)B2S3 Glasses

Wide composition range studies of the IR spectra of x Na₂S + (1 – x )B₂S₃ glasses are reported for the first time. Glasses can be prepared in two composition regions: 0 x 0.33 in a low-alkali region and 0.55 x 0.80 in a highalkali region. The structures of glasses in the former region are dominated by the creation of tetrahedral boron units similar to those observed in the alkali borate glasses. For pure B₂S₃, a large fraction of six-membered rings is found, as in glassy B₂O₃. As alkali is added, the vibrational frequency of the six-membered ring mode decreases, but not the intensity, and a new band grows in which is used to propose, by analogy with the alkali borate glasses, that the fraction of tetrahedral borons increases with alkali sulfide content. These observations suggest that isolated six-membered rings persist even in the presence of tetrahedral borons. For the high-alkali glasses, both the six-membered rings and tetrahedral boron structures are destroyed in preference to the formation of isolated orthothioborate groups, Na₃BS₃. The IR spectra of the high-alkali glasses show a monotonic increase in symmetry and simplicity, indicating an increase in structural simplicity as the orthothioborate composition is approached. For the orthothioborate composition, both glass and polycrystal can be prepared. The IR spectra of the two phases are very similar, with the glass exhibiting a broadened absorption envelope.     

Gamma-Induced Absorption and Structural Studies of Arsenic Borate Glasses

Gamma-induced coloration in borate glasses containing arsenic was studied to secure information on: ( a ) the effect of addition of As₂O₃ on the induced coloration of the alkali borate base glass, and ( b ) the possibility of using radiation-induced coloration in studying structural changes. At concentrations of less than 10 mole % As₂O₃, arsenic takes network-modifying positions and at concentrations greater than 10.0 mole % As₂O₃, it takes network-forming positions. Between 15.0 and 25.0 mole % As₂O₃, an additional change in the structure was detected. This change may be confined to the mode of arrangement of the structural units associated with the formation of groups or compounds. Additional studies based on infrared absorption, ultraviolet absorption edge, and density measurements, as well as the chemical analysis of the glasses, confirmed the structural changes suggested from irradiation studies.     

Effects of the Weak Absorption Tail on the Transmission Loss of Ge–Sb–Se Optical Fibers

Selenide glass optical fibers were fabricated for Ge₃₀Sb₁₀Se₅₈S₂ and Ge₂₀Sb₁₀Se₇₀ glasses. Their transmission loss has been measured and compared with the theoretical attenuation loss that was calculated taking into account the electronic transition absorption, Rayleigh scattering, and multiphonon absorption. A low attenuation loss of the Ge₂₀Sb₁₀Se₇₀ glass composition in 1.2–1.7 μm range has been expected due to its high optical band gap energy compared with the Ge₃₀Sb₁₀Se₅₈S₂ glass. However, the measured attenuation loss of the Ge₃₀Sb₁₀Se₅₈S₂ glass fiber was ∼13 dB/m at 1.5 μm while Ge₂₀Sb₁₀Se₇₀ glass showed ∼82 dB/m. An enhanced weak absorption tail due to the localized states of the Ge₂₀Sb₁₀Se₇₀ glass was responsible for this behavior. Structural defects are related to the localized states and discussed for the present glass compositions.     

Compositional Dependence of Absorption and Fluorescence of b3+ in Oxide Glasses

The integrated absorption cross section, the spontaneous emission probability, and the stimulated emission cross section of Yb³⁺ were determined in silicate, phosphate, borate, germanate, aluminate, gallate, and ZBLAN host glasses. The compositional dependence of the stimulated emission cross section of the ²F_5/2→²F_7/2 transition is determined mainly by the integrated absorption cross section in the glasses. A peak stimulated emission cross section above 1 pm², which is the highest value in glasses, was obtained in a gallate glass with a composition of 40K₂O·20Ta₂O₅. 40Ga₂O₃. The factors affecting the integrated absorption cross section are discussed using the Judd-Ofelt parameters of Er³⁺ calculated in previous studies.     

Phase Relations and Glass Formation in the System PbO-GeO,

Phase relations in the system PbO-GeO₂ were determined using the quenching technique. The five compounds detected were: 4PbO-GeO₂, 3PbO-2GeO₂, PbO-GeO₂, and PbO-4GeO₂. The 3:2 and 1:1 compounds melt congruently at 744° and 799°, respectively. The 4:1 compound melts incongruently at 726°C to PbO plus liquid, whereas the 1:4 compound melts incongruently to GeO₂ plus liquid at 790°C. The 1:2 compound has a temperature range of stability between 707° and 730°. The data indicate that no liquid immiscibility gap exists in the system. Indices of refraction for glasses in the system were compared with lead silicate glasses. An addition of ∼65%PbO to GeO₂ is required to prepare a glass with an index near 2.0 whereas with SiO₂, ∼85% PbO is required. It appears that the lead germanate glasses have higher indices than all other two-component oxide glasses. The addition of PbO to GeO₂ decreases the rutile-to-quartz transformation temperature from 1000°C for pure GeO₂ to 990°C. Infrared spectra of lead germanate glasses (∼60w% PbO) show that transmission is good up to 5.5μ but decreases drastically between 5.5 and 6.5μ.     

Optical Absorption Characteristics of Ni2+ in Mixed-Alkali Borate Glasses

Nickel-containing mixed-alkali borate glasses were prepared and their spectral absorption in the visible and near-ir were measured and used to determine the ligand field strength, Racah parameter, and state of coordination of Ni²⁺ ions. The change in these parameters with alkali content is discussed in terms of mixed-alkali effect. Nickel ions were found to occupy octahedral sites in the 20 mol% (Li₂O+Na₂O) glasses, whereas in the 30 mol% (Na₂O+K₂O) glasses Ni^Z+ ions are believed to occupy both octahedral and tetrahedral sites. In most cases slight deviations were observed which increased with increasing alkali content. The results obtained suggest that the substitution of one alkali for another in alkali borate glasses did not produce gross alterations of the glass network sufficient to induce deviations from linearity in property-composition relations.     

Dielectric Studies of Some Borate and Phosphate Glasses

Some borate glasses, with sag points of 350° to 500°C., of high specific resistance and low power factor have been prepared. The power factor of the glasses has been measured to 250° C., and the resistivity has been measured up to temperatures approaching the transformation region. Borate glasses have higher resistivities and power factors than phosphate glasses. An increase in sag point of lead borate glasses by substitution of PbO with BaO, Al₂O₃, or SiO₂ improves their dielectric properties. Depending on the type of glass, the dielectric constant varies linearly with the density of the glass.     

Infrared Spectra and Atomic Arrangement in Fused Boron Oxide and Soda Borate Glasses

The infrared absorption spectra of fused B₂O₃ and of a series of soda borate glasses are presented. These spectra were obtained using vacuum-pressed briquettes of the powdered glass and powdered KBr. The spectrum of fused B₂O₃ shows quite definitely that this glass does not consist of a completely continuous triangularly coordinative network. It is shown that hydrogen bonds play an important part in the atomic arrangement of the glasses of zero or low soda content. The B₂O₃ glass apparently consists of complexes of an approximate unit (B₉O₁₄)- held together by hydrogen bonds. One in nine borons is tetrahedrally coordinated. The glasses of low soda content are similar. The spectra for soda concentrations greater than 15% did not permit the determination of the atomic arrangement with exactitude, but it is shown to be quite different from that found in glasses with 10% Na₂O or less.