Photoluminescence and structural studies on Na2O–PbO–SiO2 glasses

PbO_x[(Na₂O)_0.25(SiO₂)_0.75]_1−x glasses (with x = 0.1–0.30) were prepared by a conventional melt-quench method and characterized by UV–visible optical absorption, photoluminescence and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) studies. It has been confirmed that the increased number of non-bridging oxygen atoms brought about by the increase in Q² structural units of silicon is responsible for the shifting of the wavelength corresponding to the onset of absorption, as PbO concentration increases in the glass. Emission in the visible region (400–450 nm), from these glasses has been attributed to the presence of L-centers, whose the peak maxima and line widths systematically shift to higher values by incorporating Pb²⁺ along with Na⁺ in the network modifying positions. All the Pb²⁺ ions in these glasses occupy only the network modifying positions, as revealed by the identical chemical shift values of Qⁿ structural units of silicon with increase in PbO concentration. In contrast to binary lead silicate glasses, no luminescence has been observed for comparable concentration of PbO, possibly due to the significant quenching of Pb²⁺ ions in the excited state.     

Reflection spectra of various kinds of oxide glasses and fluoride glasses in the vacuum ultraviolet region

Reflection spectra of silicate, borate, phosphate, fluorophosphate and fluoride glasses are studied in the spectral region of 2–13 eV in order to understand their dispersion behaviors in the visible region from the point of view of atomic structures.The absorption bands due to bridging oxygen ions or fluorine ions are found at 11.6 eV and 10.4–9.5 eV in silicate glasses, at 10.2 and 8.8 eV in borate glasses, at 9.5 eV in phosphate glasses, at 11.2 eV in fluorophosphate glasses and at 11 eV in fluorozirconate glasses.In silicate glasses, the bands due to nonbridging oxygen ions are found in the region 8.8-4.9 eV. They shift to lower energies with increasing ionic radius, in the order of Ca²⁺, Sr²⁺ and Ba²⁺, for the glasses containing low valency cations, while they shift to higher energies with increasing ionic radius, in the order of Ti⁴⁺, Zr⁴⁺ and Th⁴⁺ or in the order of Nb⁵⁺ and Ta⁵⁺, for the glasses containing high valency cations.In glasses containing large amounts of PbO, strong bands due to PB²⁺ ions appear in the lower energy regions of 6.3–5.6 eV and 5.2–4.7 eV.     

ESR and optical absorption of Cu2+ in Na2OSiO2 glasses

ESR and optical absorption spectra of Cu²⁺ in xNa₂O(100?x)SiO₂ glasses were measured, where x ranges from 12 to 70 mol% Na₂O. This glass system was divided into three composition regions, 12 ? x ? 37, 37 ? x ? 55 and 55 ? x, from the composition dependence of the ligand field transition energy and spin hamiltonian parameters of Cu²⁺. Two boundary compositions (37 and 55 mol%) between the two adjacent regions agreed with the eutectics in the equilibrium phase diagram. Two types of Cu²⁺-complexes, with less basic ligands (HFS-1) and much more basic ones (HFS-2), were detected in ESR for ultra-high soda glasses (x ? 55). The distribution of the ESR parameters due to the fluctuation of ligand fields was negligible for HFS-2 compared with that for other glasses. The Cu²⁺ ion responsible for HFS-2 was considered to distribute in the microphase of orthosilicate. Imagawa's basicity, the covalency of the bondings between Cu²⁺ and ligands, was calculated by using Maki and McGarvey's analysis. The basicity of σ-type symmetry remained constant, irrespective of the glass composition, and the value was identical with those for other oxyanionic glasses. The π-type basicity was also constant for the glasses of x ? 55. Two different basicities, each corresponding to HFS-1 or 2, were obtained for the glasses of x ? 55. The value derived from HFS-1 was identical with those for x < 55 glasses, whereas that derived from HFS-2 suggested the formation of much more basic ligands.     

Raman spectra and structure of sodium aluminogermanate glasses

Polarized Raman spectra of x NaAlO₂·(100 ? x) GeO₂ glasses (x = 0, 5, 10, 15, 20, 25, 33, 42, and 50) are presented. Analyses of the Raman data indicate that the aluminogermanate glasses have three-dimensional network structures consisting of interconnected AlO₄ and GeO₄ tetrahedra; Na⁺ ions are present in cavities and charge balance the Al³⁺ ions. Systematic changes are observed in the frequencies, intensities and polarization characteristics of spectral bands with variations in the NaAlO₂ content of these glasses. The antisymmetric stretching mode [ν_as (TOT), where T = Al, Ge] in the high-frequency region of the spectra (800–1000 cm^?1) appears as a doublet consisting of well-defined bands in the spectra of glasses along the entire join. Both components of the high-frequency doublet shift to a lower frequency with increasing NaAlO₂ content, indicating that the ν_as (GeO₄) and ν_as(AlO₄) stretching modes are coupled. The variations in the TO force constants and TOT bond angles with change in composition most likely cause the bands to shift. The frequencies of the Raman bands of sodium aluminogermanate glasses are compared with those of the corresponding bands in isostructural sodium gallogermanate glasses. On the basis of this comparison, the origin and delocalization of the vibrational modes producing characteristic Raman bands in the spectra of these glasses are discussed. The changes observed in the Raman spectra of aluminogermanate glasses with variation in NaAlO₂ content are analogous to those observed in the spectra of glasses along the NaAlO₂SiO₂ join.     

Bond character and properties of the mixed alkali system Na2OK2OAl2O3SiO2

The mixed alkali glass system Na₂OK₂OAl₂O₃SiO₂ was investigated. Density, transformation temperature, refractive index, and chemical durability were studied. Optical absorption and ESR spectra of the CuO-doped glasses were determined.Calculations of the polarizability of O^2?, bonding parameters of the Cu²⁺ complex, and the packing density are presented. It was found that for the mixed alkali glasses, the oxygen- alkali bond has a more ionic character than expected from additivity. This fact enables the non-linear changes of the refractive index, of the shift of the Cu²⁺ absorption band, and of the covalency to be interpreted as the Na mole fraction is varied. It is also possible to explain qualitatively the density, T_g and chemical durability non-linear variations with change of the Na content by the ionicity deviations of the bond character and the postulated pairs of Na⁺ and K⁺ ions in the mixed alkali glasses.     

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.     

Study of the alkaline environment in mixed alkali compositions by multiple-quantum magic angle nuclear magnetic resonance (MQ–MAS NMR)

45S5 Bioglasses of the composition 46.1 SiO₂–2.6 P₂O₅–26.9 CaO–(24.4 ? x) Na₂O–xMe₂O (Me = Li or K) have been investigated using MAS NMR and MQ–MAS NMR methods. The analysis of the ²⁹Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Q_n=2,3 species. The ³¹P MAS NMR spectrum reveals the effect of both Na and Ca ions. The chemical shift of the observed ³¹P signal is intermediate between those of Na₃PO₄ (near 10 ppm) and Ca₃(PO₄)₂ (near 3–0 ppm) species. The ²³Na MAS NMR spectra were observed in the alkali oxide composition: 24.4 Na₂O, 12.2 Na₂O–12.2 K₂O and 12.2 Na₂O–12.2 Li₂O. The substitution of Na with Li or K was done to determine the extend of alteration of the glass structure. This goal was best accomplished by ²³Na MQ–MAS NMR. The two-dimensional spectra revealed three sites in the 24.4 mol% Na₂O glass. These sites were not resolved in the 1D MAS NMR spectroscopy. In the mixed glasses, only two sites were obtained.     

Spectroscopic properties of Yb3+ ions in halogeno-sulfide glasses

In this work, we report the optical properties of Yb³⁺ ions in halogeno-sulfide glasses of composition (75 − x)GeS₂–25Ga₂S₃–xCsCl (x = 5%, 10%, 15%, 20%, and 25% CsCl). This study includes an analysis of the influence of halide concentration on the absorption and emission cross-sections and lifetimes of Yb³⁺ ions. A blue shift of the absorption and emission bands and a decrease of the absorption and emission cross-sections and transition probability are observed as the halide concentration increases in the glass.     

Magnetic behavior and microstructure of x%V2O5·(100−x)%As2O3 glasses

The magnetic properties and microstructure of x%V₂O₅·(100−x)%As₂O₃ glasses with x varying in the range 40 to 90 mol% were investigated in order to elucidate their magnetic ordering. Weak antiferromagnetic interactions between V⁴⁺ ions were observed. Glasses with x ⩾ 60 separated into two glassy phases. The effect of microstructure on magnetic properties of these glasses was investigated. Phase separation increases with increasing V₂O₅ content and produces a broadening of the EPR line width of glasses with high vanadium content (x > 70). The c = V⁴⁺/V_total ratio of x%V₂O₅·(100−x)%As₂O₃ glasses, determined from EPR and chemical analysis, are considerably greater than those usually reported for x%V₂O₅·(100−x)%P₂O₅ glasses.     

Influence of valence and coordination of manganese ions on spectral and dielectric features of Na2SO4–B2O3–P2O5 glasses

Sodiumsulpho borophosphate glasses with composition (40 ? x)Na₂SO₄–30B₂O₃–30P₂O₅: xMnO with x ranging from 0 to 5.0 mol% were manufactures. Dielectric spectra have been studied over a wide frequency range of 10²–10⁵ Hz and in the temperature range within 30–250 °C. The valance states of manganese ions and their ligand coordination in the glass network have been investigated using optical absorption, luminescence and ESR spectroscopy. The analysis of the these results has indicated that the manganese ions exist both in Mn²⁺ as well as in Mn³⁺ states and occupy prevailingly octahedral positions and serve as modifiers similarly to Na⁺ ions The values of dielectric parameters (dielectric constant, ε′(ω), loss tan δ and ac conductivity, σ_ac) were found to increase with increasing MnO content. They play a role of modifiers similarly to Na⁺ ions, create bonding defects and free ions viz., [SO₄]^2?, [POO_1/2O₂]^2?, [POO_0/2O₃]^3–, Na⁺ and (NaSO₄)^?. The migration of these charge carriers would build up space charge polarization and may be responsible for the enhanced dielectric parameters. The ac conductivity also is enhanced with increasing MnO content. The mechanism responsible for such increase is well explained based on the modifying action of Mn²⁺ ions.     

Mössbauer study of europium in fluorozirconate glass

¹⁵¹Eu Mössbauer spectra of fluorozirconate glasses of nominal composition 0.61 ZrF₄ · (0.32 ? x) BaF₂ · x EuF₂ · 0.07 ThF₄ with x = 0.10 and 0.20 show that Eu²⁺ is present in sites with isomer shifts in the range ?15.5 to ?12.9 mm/s, corresponding to EuF bond lengths of 2.3–2.8 Å and a coordination number ranging from 8 to 12. The glasses contain a minor amount (～10%) of Eu³⁺ in well-defined sites. Effective Debye temperatures deduced from the recoilless fractions for the two ions are θ_D²⁺ = 145 K and θ_D³⁺ = 261 K. The differences in coordination and bonding indicate that trivalent eurpoium is a network former, whereas the divalent ions are network modifiers.     

Copper redox behavior, structure and properties of copper lead borate glasses

Copper oxidation states, structure and properties of xCuO · (50-x)PbO · 50B₂O₃ glasses were investigated. Both infrared (IR) and ¹¹B magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies were employed to determine the tetrahedral BO₄ fraction in the glasses as a function of CuO content. IR study indicates that the replacement of Pb²⁺ by Cu²⁺ ions increases the BO₃ units by converting BO₄- containing groups into ring type metaborate groups. The oxidation states of copper ions in the glasses have been studied using both X-ray photoelectron spectroscopy (XPS) and the wet chemical method. For high CuO containing (?30 mol%) glasses, high Cu⁺ ion concentrations (Cu⁺/Cu_tot.>0.3) result in a relatively slow disproportionation of B⁴-containing groups because of the small coordination number of Cu⁺ compared to Cu²⁺ ions. Effects of both glass structure and redox states of copper ions on glass properties including density, Vickers’ hardness, coefficient of thermal expansion, and chemical durability have been discussed.     

Structure-property correlation in (50 − x)Na2O–50P2O5–xCoCl2 glassy systems

Ternary sodium–cobalt–phosphate glasses of the composition (50 − x)Na₂O–50P₂O₅–xCoCl₂ with x varying between 0 and 15 mol% prepared by melt quenching have been characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) techniques. Thermal (T_g, T_c) and electrical properties have been investigated. Infrared spectra reveal the formation of metaphosphate glasses (Q² tetrahedral units) with symmetric bridging oxygen (P–O–P) and non-bridging oxygen (P–O⁻). The spectra also indicate the formation of P–O–Co bonds in the metaphosphate glasses that replace P–O⁻–Na⁺ bonds. The results of thermal studies correlate with these FT-IR findings and support the formation of P–O–Co bonds and an increased cross-link density with increasing CoCl₂. This results in enhanced chemical durability and increased T_g and T_c of the glasses. The electrical conductivity parameters upon changing the composition have been correlated with structural changes in the glass matrix.     

Network structure of sodium and potassium borosilicate glass systems

Molar volumes and optical absorption spectra of Ni²⁺ ions were measured for sodium and potassium borosilicate glasses of the compositions xR₂O·B₂O₃·rSiO₂ (0.01 < x < 2.0; r = 1 and 2), where parameters x and r represent respectively the molar ratios R₂O/B₂O₃andSiO₂/B₂O₃. The presence of structural groups was discussed from the results. It was confirmed that addition of an alkali oxide changed BO₃ units to RBO₄ units in the range x < 0.55 for r=1 and x < 0.6 for r=2, while it created ROSiO₃ units in the range $\text{0.55 < x < 0.8}\text{for}\text{r=1}\text{and}\text{0.6}\text{x}\text{?}\text{< 0.9}\text{for}\text{r=2}$. In the range x > 0.8 for r=1 and x > 9 for r=2, ROSiO₃ and ROBO₂ units were created by the alkali addition. Here ROBO₂ units were also formed as a result of self-decomposition of RBO₄ units. The volume of void associated with a BO₄ unit was calculated and compared with the size of sodium and potassium ions. It was shown that sodium ions were small enough to be accommodated in the void whereas potassium ions were too large. This could explain the composition dependence of the molar volume of the sodium and potassium borosilicate glasses in the composition range x < 0.55 for r = 1 and x < 0.6 for r =2.     

Influence of alkali and alkali-earth metal oxide substitutions on the properties of lithium-iron-phosphate glasses

The influences of different alkali and alkali-earth oxide substitutions on the properties of lithium-iron-phosphate (LIP) glasses have been studied. Na₂O, K₂O, MgO, CaO and BaO were used to substitute Li₂O to prepare LIP glasses with molar compositions of (20 − x)Li₂O − xR₂O(RO) − 30Fe₂O₃ − 50P₂O₅ (x = 2.4, 4, 5.6 and 7.2). The glass transition temperature (T_g) was determined by the differential thermal analysis technique. The density and chemical durability of the prepared glasses were measured based on the Archimedes principle and the weight losses after the glasses were boiled in water. The results show that T_g decreases with the initial substitutions, whereas the density and chemical durability increase. The diminution of the aggregation effect of Li⁺ ions on the glass structure due to the decrease in Li⁺ concentration, the larger molecule weights of the substitutes, the mixed-alkali and depressing effects as well the slower mobility of substitute ions mainly contribute to the initial changes in T_g, density and chemical durability of the LIP glasses, respectively. Further increasing the amounts of substitutes brings about increasing diminution of the aggregation effect of Li⁺ ions and breakage of the glass network on the one hand and increasing amounts of substitutes with larger molecule weights and ion radii on the other hand. Both aspects influence the glass properties oppositely and consequently non-monotonic variations in the properties of LIP glasses with the substitutions are observed.     

Optical properties and valence change of samarium ions in a sol–gel Al2O3–B2O3–SiO2 glass by femtosecond laser irradiation

10Al₂O₃–5B₂O₃–85SiO₂–xSm₂O₃ glasses were prepared by the sol–gel method. The emission spectra of the glasses indicate that the quench concentration of the Sm³⁺ ions is about 0.2 mol%. The emission spectra of the glasses after high-temperature treatment with H₂ gas exhibit the coexistence of the Sm³⁺ and Sm²⁺ ions. We observed the strong emission line of the Sm²⁺ ions and the emission band of the non-bridging oxygen hole center when the glasses were exposed to a femtosecond laser. It indicates that some Sm³⁺ ions were reduced to Sm²⁺ ions by femtosecond laser pulses and non-bridging oxygen hole centers were formed. The ⁵D₀–⁷F₀ emission line of the Sm²⁺ ions by femtosecond laser irradiation shows a red shift, compared with the emission of the Sm²⁺ ions by reduction with H₂ gas. The strong absorption band and weak, sharp absorption lines in the range from the UV to IR come from charge transfer and the transition from the ⁶H_5/2 state to the various excited states of the Sm³⁺ ions. The reduction mechanism of Sm³⁺ ions is discussed.     

Majority charge carrier reversal and its effect on thermal and electron transport in xV2O5–(1 − x) As2O3 glasses

DC resistivity, thermopower and optical absorption of xV₂O₅–(1 ? x) As₂O₃ (0.58 ≤ x ≤ 0.93) glasses have been studied as a function of composition. The transport mechanism in these glasses has been identified to be a combination of hopping of small polarons between V⁴⁺ and V⁵⁺ sites and small bipolarons between As³⁺ and As⁵⁺ sites respectively. Electrical conductivity is found to be more of a function of vanadium content than arsenic concentration in the glasses, indicating that the contribution of bipolarons to the conductivity is negligible. Thermopower has also been found to be sensitive to the composition of the glasses. At low vanadium concentrations, the thermopower is negative, which exhibits a sign reversal as vanadium concentration is increased (at x = 0.7). An important feature of these glasses is that the thermopower is not a function of [V⁵⁺]/[V⁴⁺] ratio, as is normally observed in vanadate glasses, and such a phenomenon suggests that the arsenic ions (bipolarons) in these glasses contribute to the thermal transport phenomena in a significant way.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x and their ordering: 9. The defect crystal and real structure of quenched fluorite phases Sr1 − x Ce x F2 + x (x = 0–0.5)

A Sr_0.7Ce_0.3F_2.3 crystal (CaF₂ type, sp. gr. $Fm\bar 3m$ ), obtained by quenching from melt, has been studied for the first time by X-ray diffraction. Fluorine vacancies and interstitial anions are found in the 8c and 32f sites, respectively. The defect ratio in the Sr_0.7Ce_0.3F_2.3 structure corresponds to the tetrahedral cluster configuration of defects {Sr_{4 ? n} Ce _n F₂₆}. The defect structure of quenched (at a rate of ～25 K/min) crystal differs from that of a crystal grown from melt (cooling at a rate of ～3 K/min) by the displacement of some cations (presumably Ce³⁺) along the threefold axis to the 32f site and the anisotropy of thermal vibrations of ions in the cluster core (F _int(32f)3). The concentration dependence of the lattice parameters of quenched Sr_{1 ? x} Ce _x F_{2 + x} phases (x = 0–0.5) is described by a third-order polynomial: a = 5.80009 + 1.166518 × 10^?3 x ? 1.124969 × 10^?5 x ² + 8.258155 × 10^?8 x ³. The compositional dependence of microdistortions is also nonlinear; maximum microdistortions are observed in the SrF₂ crystal. They decrease with an increase in the cerium concentration x to ～ 0.35. The minimum in the range x = 0.30–0.35 correlates with a composition corresponding to the peak (at x ～ 0.29) in the melting curves of the fluorite phase estimated from the phase diagram of the SrF₂-CeF₃ system (the method of thermal analysis).     

Catalysis and proton-conduction of novel phosphate glasses

The performance of phosphate glasses as a catalyst for water decomposition and a proton conductor was investigated. Glasses with a composition of 30Na₂O–10BaO–30P₂O₅–(30?x)WO₃–xNb₂O₅ (5 < x < 25) decompose water vapor and generate hydrogen at 500 °C. The best decomposition performance was observed on a specimen with the Nb₂O₅ composition of x = 15. A part of hydrogen produced on the glass surface changes to protons by reducing W⁶⁺ ions and penetrates into the glass. The electron is the dominant charge carrier in the electric conduction of W-rich glasses, whereas proton conduction is predominant in Nb-rich glasses in hydrogen atmosphere. A Raman scattering experiment revealed that Nb contributes to depolymerize the –P–O–P– chains in the phosphate glass producing non-bridging oxygen. A possible model was proposed for the water decomposition and proton conduction processes.     

Effect of boron oxide addition on the Nd environment in a Nd-rich soda-lime aluminoborosilicate glass

The environment of Nd³⁺ ions has been studied using optical absorption spectroscopy and EXAFS at the Nd L₃-edge, in a series of soda lime aluminoborosilicate glasses with increasing B₂O₃ content. The proportion of BO₄ units has been determined by ¹¹B MAS NMR in an equivalent glass series with La³⁺ ions replacing the majority of Nd³⁺ ions, and complementary information has been obtained by measuring the Nd³⁺ decay fluorescence times in these latter glasses. In these glasses with low Al₂O₃ content, the R′ ratio, with R′ = [Na₂O^exc] / [B₂O₃] and [Na₂O^exc] = [Na₂O] − [Al₂O₃] − [ZrO₂], plays a key role in controlling the structural organization and crystallization resistance, in a similar way as the R ratio in the Dell and Bray model of sodium borosilicate glasses. At R′ > 0.5, the Nd³⁺ ions are located in a mixed silicate-borate environment and, by slow cooling of the melt, they tend to crystallize within a silicate apatite phase close to the Ca₂Nd₈(SiO₄)₆O₂ composition. At R′ < 0.5, the structural results are compatible with Nd³⁺ ions located in a borate-type environment (not excluding Si neighbors), and, by slow cooling of the melt, they segregate with Ca²⁺ ions within a Si-depleted separated borosilicate phase.