FTIR and UV–VIS optical absorption spectra of gamma-irradiated MoO3-doped lead borate glasses

Structure and optical properties of MoO₃-doped lead borate glasses which contain high PbO content (60, 70 and 80%) have been studied using Fourier transform infrared (FTIR) and ultraviolet–visible (UV–VIS) spectroscopic tools. FTIR spectra reveal absorption bands which are characteristic for various structural units of borate network, mainly BO₃ triangles and BO₄ tetrahedra, in addition to the PbO_n (where n = 3 and/or 4) structural units. UV–VIS optical absorption spectra reveal broad intense charge transfer UV bands due to Pb^2 + ions in the range 320–385 nm. Within this range, molybdenum ions, preferably Mo^3 + and Mo^5 +, can interfere at about 360–385 nm. Additionally, molybdenum ions give a weak visible band at about 850–860 nm. The optical absorption spectra of the studied glasses show marked resistance to successive gamma irradiation up to 5 Mrad. This shielding behavior can be related to the present high content of the high atomic mass Pb^2 + ions. Changes in the atomic structure before and after gamma irradiation are described and explained.     

Ca–Mg mixing in aluminosilicate glasses: An investigation using 17O MAS and 3QMAS and 27Al MAS NMR

To better understand non-framework cation mixing in Ca–Mg aluminosilicate glasses, ¹⁷O MAS and 3QMAS NMR studies were done on glasses on the Mg₃Al₂Si₃O₁₂–Ca₃Al₂Si₃O₁₂ join as well as several compositions with lower Al/Si ratios. While not all of the oxygen sites are fully resolved, the non-bridging oxygen associated with two Ca and one Mg cations is under-represented relative to that predicted by a model assuming random Ca/Mg mixing. Therefore, local non-bridging oxygen environments are rich in Mg, and extra Ca must be associated with charged bridging oxygens such as Al–O–Si. The deviation from random mixing increases as the Al/Si ratio decreases and as X_Mg approaches 0.50, suggesting a reduction in configurational entropy that may be compensated for by other sources, including mixing of network forming cations. Al–O–Al is detected, and appears to increase with increasing X_Mg and increasing Al/Si. High field ²⁷Al MAS NMR also shows that these glasses all have substantial concentrations of ^[5]Al, but no detectable ^[6]Al (0.5% detection limit). The amount of ^[5]Al increases non-linearly as X_Mg increases and very slightly as Al/Si increases.     

Micro-structural studies of GeSe2–Ga2Se3–MX (MX = CsI and PbI2) glasses using Raman spectra

Microstructure of the chalcohalide glasses: GeSe₂–Ga₂Se₃–CsI and GeSe₂–Ga₂Se₃–PbI₂ ternary system were investigated by Raman spectra, lifetime of Dy³⁺ infrared emission and glass transition temperature (T_g). The evolution of the Raman spectra shows that the fundamental structural groups of these studied glasses consist of [Ge(Ga)Se₄] tetrahedral and some complex structure units [Ge(Ga)I_xSe_4?x](x = 1–4). The x value varied when the different iodide was added in Ge–Ga–Se matrix. For GeSe₂–Ga₂Se₃–CsI glasses, the [Ge(Ga)I_xSe_4?x](x = 1–4) mixed-anion tetrahedral and [Ga₂I₇]^? units occurred. For GeSe₂–Ga₂Se₃–PbI₂ glasses, the [Ge(Ga)I₂Se₂], [Ge(Ga)I₃Se] units can be formed. The changes of Dy³⁺ infrared emission lifetime and T_g support the results. Additionally, [PbI_n] structural units will be formed in GeSe₂–Ga₂Se₃–PbI₂ glasses due to high form-ability of these units when the PbI₂ content is high.     

Structural role and coordination environment of Fe in Fe2O3–PbO–SiO2–Na2O composite glasses

The structural role, coordination geometry and valence of Fe in a series of Fe₂O₃–PbO–SiO₂–Na₂O glasses are studied by means of Fe-K-NEXAFS and EXAFS spectroscopies. Parameters for the study are the concentration of the Fe and Pb-oxides, the SiO₂/Na₂O ratio and the cast temperature. The EXAFS and NEXAFS results reveal that the role of Fe³⁺ depends on the concentration of Fe₂O₃. More specifically, in most of the studied quaternary systems, the Fe³⁺ ion is a glass former, i.e. the Fe atoms belong to FeO₄ tetrahedra that participate in the formation of the glassy network. The role of Fe as an intermediate oxide is identified only in one sample with 20 wt% Fe₂O₃, where ～80 at.% of the Fe atoms are tetrahedrally coordinated with O atoms, while the remaining ～20 at.% of the Fe atoms occupy octahedral sites. It is also revealed that the tetrahedral coordination of Fe in the vitreous matrix is destroyed when a number of parameters is altered, such as the T_cast, the (Fe + Si)/O and the SiO₂/Na₂O ratio.     

Structural dependence of ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses

Ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses at the wavelength of 820 nm has been measured using femtosecond time-resolved optical Kerr (OKE) technique. The results show that Ge–Ga–Ag–S glasses have large third-order optical nonlinear susceptibility, χ⁽³⁾ and the response time is also subpicosecond, which are predominantly due to the ultrafast distortion of electron cloud surrounding the balanced positions of Ge, Ga, Ag and S atoms. What’s more, a strong dependence of χ⁽³⁾ on the composition and microstructure of these glasses was found which shows that [GeS₄] and [GaS₄] tetrahedra play an important role on the third-order optical nonlinearity. These Ge–Ga–Ag–S chalcogenide glasses would be expected as promising materials applied on all-optical switching devices.     

Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.     

Evaluation of chemical durability,thermal properties and structure characteristics of Nb–Sr-phosphate glasses by Raman and NMR spectroscopy

Thermal properties, water durability and structure of Nb₂O₅–SrO–P₂O₅ glasses containing 0–25 mol% Nb₂O₅ and 35–60 mol% SrO were explored aiming to develop high refractive index optical glasses. Structure studied using Raman and NMR spectra reveals that by increasing Nb₂O₅ content, niobium plays the role as intermediate. Nb⁵⁺ tends to break P–O–P and O–P–O bonds forming [NbO₆] structure. Thus fractions of Q³ and Q² decrease, while Q¹ fraction increases. Furthermore the Q⁰ fraction replaces the lessened Q³ fraction. As P₂O₅ content is reduced to 30 mol%, partial [NbO₆]_octa turns into [NbO₄]_tetra and partial (Nb–O)_short-octa becomes (Nb–O)_short-tetra bond to stabilize the glass structure. Glass-transition and softening-temperatures of the glasses increase by increasing SrO and Nb₂O₅ contents. Thermal expansion coefficient increases by increasing SrO while decreases with Nb₂O₅ content. Water durability is enhanced as increasing Nb₂O₅ and SrO contents. Properties of the glasses correlate well with the worked out structure.     

Spectroscopic studies of tungsten ions in PbO–PbF2–SiO2 glasses

40PbO–(10 ? x)PbF₂–50 SiO₂:xWO₃ (where x = 1 to 7 mol%) glasses are prepared in the glass forming region. Spectroscopic studies (UV–Vis absorption, ESR, IR) are carried out for these glasses. Interesting changes are observed in the spectroscopic parameters of these glasses when the concentration of WO₃ is changing in the glass matrix. Two absorption bands are observed around at 830 and 620 nm. ESR signal are measured at room temperature for these glasses, the strength of the signal is increased and hyperfine splitting is resolved with increasing the concentration of WO₃ in the glass matrix. IR transmission gives valuable information about the nature of bonds in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

Raman and NMR study of bioactive Na2O–MgO–CaO–P2O5–SiO2 glasses

The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na₂O–MgO–CaO–P₂O₅–SiO₂ are presented. The Raman spectra show clear changes in the Si–O–Si vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the Si–O–NBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca²⁺ and Mg²⁺. The silicate matrix also contains both types of two-valent cations and consists of Q² and Q¹ units. Similarly, the Na₂O-containing samples contain isolated orthophosphate units in a silicate matrix (Q² and Q³ units), both charge-compensated by mixed cations Ca²⁺ and Na⁺. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Structural study of AsS2–Ag glasses over a wide concentration range

(As_0.33S_0.67)_100-xAg_x (0 ≤ x ≤ 28) bulk glasses showing micro-phase separation in a wide concentration range have been studied by X-ray diffraction, neutron diffraction and extended X-ray absorption fine structure measurements. The AsAgS₂ composition, which forms a homogeneous glass, is modeled with the reverse Monte-Carlo simulation technique. It is established that Ag prefers the environment of S; Ag―As bonding cannot be observed. Similarly to the AsAgS₂ crystalline modifications smithite and trechmannite, the main structural units of the glass are AsS₃ pyramids. The covalent network of As and S atoms becomes fragmented in the glassy AsAgS₂ unlike in the glassy AsS₂. The environment of Ag atoms in the AsAgS₂ glass differs from that in the crystalline state. In average, each Ag atom has four nearest neighbors, three of them being S and one being Ag.     

Structural role of MgO and PbO in MgO–PbO–B2O3 glasses as revealed by FTIR; a new approach

FTIR spectra of three MgO–PbO–B₂O₃ glass series have been analyzed. There is a decrease in the fraction N₄ of four coordinated boron with increasing the MgO content, at the expense of PbO. A new technique has been presented to make use of the N₄ data and follow the change in the modifier and former fractions of PbO and MgO. These fractions change markedly, at different rates, with the glass composition. The fraction of modifier MgO is always less than the MgO content, which suggests a former role of this oxide in the studied glasses. The ability of the glass to include MgO increases with increasing PbO content.     

Structural modifications induced by addition of copper oxide to lead–phosphate glasses

xCuO(1-x)[P₂O₅·PbO] glass system with 0 ≤ x ≤ 50 mol% was prepared and investigated by means of EPR and IR spectroscopy in order to evidence the structural changes induced by different amounts of copper ions. EPR spectra analysis together with EPR parameters has indicated a distorted tetragonal symmetry – named tetrahedral local symmetry – for Cu^2 + ions in the studied glasses. A change in the shape of EPR spectra was also observed as for small CuO concentration (x < 20 mol%) these glasses present an asymmetrical line typical for isolated ions and for high CuO content this line is replaced by a symmetrical one characteristic of clustered ions through dipole–dipole interactions. IR spectra of the studied glasses put in evidence a strong depolymerization effect with a gradual increase of CuO. The shift of PO asymmetric stretching vibration band to lower wave number can be explained by the increase of PO₄ tetrahedra charge density leading a more ionic and less covalent bonding.     

Photochromic behavior of Li-stabilized MoO3 sol–gels

Photochromic behavior of Li-doped MoO₃ sol–gels prepared by the peroxo sol–gel method was studied in details using various experimental techniques, including UV–vis, XRD, Raman, EPR, and XPS. The lithium doping has drastically enhanced the stability of the MoO₃ sol–gels. Upon UV-light irradiation from a high-pressure mercury lamp, the Li-doped MoO₃ sol turned from yellowish into deep blue, and the sol in ethanol exhibited much more intense color change than the sol in water. The UV-light exposure has the effect of re-arranging the structural units of MoO₃ and building up short-range order inside the solid. The formation of a blue colored bronze in the photo-irradiated sols because of the reduction of Mo⁶⁺ to Mo⁵⁺ is also evidenced by the experimental data. Based on these data, a mechanism for the photochromic behavior is proposed.     

Hardness and refractive index of Ca–Si–O–N glasses

Vickers hardness and refractive index was determined for Ca–Si–O–N glasses with 14.6–58 e/o N and 19–42 e/o Ca. By applying slow cooling rates, transparent glasses were obtained for compositions near Ca_9.94Si₁₀O_17.73N_8.14, while the majority of the glasses were opaque due to small inclusions of elemental Si and/or Ca-silicide. Determined glass densities varied between 2.80 and 3.25 g/cm³. Hardness was found to vary from 7.3 to 10.1 GPa at a load of 500 g and, respectively increase and decrease linearly with N and Ca content. The refractive index was found to increase linearly with N content from 1.62 to 1.95 and showed no significant dependence on Ca content.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Preparation and properties of chalcogenide glasses in the GeS2–Sb2S3–CdS system

In searching for new kind of photoelectric material, chalcogenide glasses in the GeS₂–Sb₂S₃–CdS system have been studied and their glass-forming region was determined. The system has a relatively large glass-forming region that is mainly situated along the GeS₂–Sb₂S₃ binary side. Thermal, optical and mechanical properties of the glasses were reported and the effects of compositional change on their properties are discussed. These novel chalcogenide glasses have relatively high glass transition temperatures (T_g ranges from 566 to 583 K), good thermal stabilities (the maximum of deference between the onset crystallization temperature, T_c, and T_g is 105 K), broad transmission region (0.57–12 μm) and large densities (d ranges from 2.99 to 3.34 g cm^?3). These glasses would be expected to be used in the field of rare earth doped fiber amplifiers and nonlinear optical devices.