Theoretical studies of the spin Hamiltonian parameters and the local structures for the tetragonal Cu centers in the LKB glasses

The spin Hamiltonian parameters (g factors g_∥, g_⊥ and the hyperfine structure constants A_∥, A_⊥) for the Cu²⁺ centers in the lithium potassium borate (LKB) glasses xLi₂O·(30 − x)·K₂O·70B₂O₃ (0 ≤ x ≤ 25) were theoretically studied using the high-order perturbation formulas of these parameters for a 3d⁹ ion in a tetragonally elongated octahedron. The [CuO₆]¹⁰⁻ clusters in the LKB glasses are found to suffer the relative elongations of about 3% along the tetragonal axis due to the Jahn-Teller effect. The concentration dependences of the g factors are illustrated by the approximately linear decrease of the cubic field parameter Dq as well as the increases of the covalency factor N and the relative elongation ratio ρ due to the slight expansion of the cell volume or bond lengths with increasing the Li₂O concentration x. Meanwhile, the slow non-linear increases of the hyperfine structure constants are described as the rough exponential increase of the core polarization constant κ with x due to the increase of the tetragonality of the systems. The theoretical spin Hamiltonian parameters and their concentration dependences show good agreement with the experimental data. To evaluate validity and applicability of the present theoretical model and formulas, the EPR results of the Cu²⁺ centers in similar lithium sodium borate (LNB) xLi₂O·(30 − x)·Na₂O·70B₂O₃ (5 ≤ x ≤ 25 mol%) glasses are also analyzed and compared with those in the LKB systems using the uniform model and formulas.     

Thermal, chemical, optical properties and structure of Er-doped and Er/Yb-codoped P2O5-Al2O3-ZnO glasses

This study was explored in series of the optical, thermal, and structure properties based on 60P₂O₅-10Al₂O₃-30ZnO (PAZ) glasses system that doped with varied rare-earth (RE) elements Yb₂O₃/Er₂O₃. The glass transition temperature, softening temperature and chemical durability were increased with RE-doping concentrations increasing, whereas thermal expansion coefficient was decreased. In the optical properties, the absorption and emission intensities also increase with RE-doping concentrations increasing, When Er₂O₃ and Yb₂O₃ concentrations are over than 3 mol% in the Er³⁺-doped PAZ system and Yb³⁺-doped concentration is over than 3 mol% for Er³⁺/Yb³⁺-codoped PAZ system, the emission intensity significantly decreases presumably due to concentration quenching, formation of the ions clustering, and OH⁻ groups in the glasses network. It is suggested that the maximum emission cross-section (σ_e) is 7.64 × 10^− 21 cm² at 1535 nm is observed for 3 mol% Er³⁺-doped PAZ glasses. Moreover, the maximum σ_e × full-width-at-half-maximum is 327.8 for 5 mol% Er³⁺-doped PAZ glasses.     

Thermodynamics of the Cu/Cu-redox equilibrium in soda-silicate and soda-lime-silicate melts

The thermodynamics of the redox equilibrium of Cu⁺/Cu²⁺ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na₂O · (100 − x) SiO₂ (x = 15, 20, 26 and 33) and (26 − x) Na₂O · x CaO · 74 SiO₂ (x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu²⁺ to Cu⁺ and Cu⁺ to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu⁺]/[Cu²⁺]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu⁺ and Cu²⁺ in octahedral coordination into the melt structure.     

Optical Properties of Bi2O3-TeO2-B2O3 Glasses

Glasses of the Bi₂O₃-TeO₂-B₂O₃ ternary system were developed and their linear and nonlinear optical properties were investigated. The absorption edges of these glasses were found to be 367-384 nm with a good transmittance in visible wavelength, although they exhibit the refractive indices as high as 1.98-2.12 at 633 nm. The absorption edges are quite steep and they are analyzed by the Urbach theory. The obtained Urbach energies of these glasses are 73-79 meV which are comparable to silica glasses. The high refractive index and its glass composition dependency are discussed according to the basics of the electronic polarizability and optical basicity. The high third order nonlinear susceptibility χ⁽³⁾ = 2.0 × 10^− 12 esu at 800 nm was also obtained in the 36Bi₂O₃-18TeO₂-46B₂O₃ glass.     

Spectral properties of PbO-P2O5 glasses

The optical absorption spectra of xPbO-(100 − x) P₂O₅ glasses where x = 5, 10, 15, 20, 25, and 30 is reported. The spectral absorption of these glasses was measured in the spectral range 300-900 nm at room temperature. Optical absorption spectra show that the absorption edge has a tail extending towards lower energies. The edge shifts nearly linearly towards higher energies with increasing PbO content. The degree of the edge shift was found to depend on the PbO content and is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. The optical energy gap increases, from 2.55 to 3.05 eV by increasing PbO content from 5 to 30 mol%. The width of the localized states is decreased by increasing PbO content.     

Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB₂O₃-(40−x)Fe₂O₃-60P₂O₅ (x = 2-20, mol%) and xB₂O₃-(100−x)[Fe₂O₃-60P₂O₅] (x = 2-20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. T_g increased with increasing B₂O₃ content for the glasses in the first series which indicates that the addition of B₂O₃ increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10⁻⁹ gr/cm² min which are comparable to that of the base iron phosphate glass. When the B₂O₃ content was above 14%, new bands related to BO₄ tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe²⁺ ions in glasses (Fe²⁺/∑(Fe²⁺ + Fe³⁺)) was found to be 23% for the base glass while it was 10-22% for the boron doped glasses.     

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.     

Structure and electrical conductivity of new Li2O-CeO2-B2O3 glasses

Fourier transformation infrared spectra, density and DC electrical conductivity of 30Li₂O · xCeO₂⋅(70 − x)B₂O₃ glasses, where x ranged between 0 and 15 mol%, have been investigated. The results suggested that CeO₂ plays the role of network modifier up to 7.5 mol%. At higher concentrations it plays a dual role; where most of ceria plays the role of network former. The density was observed to increase with increasing CeO₂ content. The effect on density of the oxides in the glasses investigated is in the succession: B₂O₃ < Li₂O < CeO₂. Most of CeO₂ content was found to be associated with B₂O₃ network to convert BO₃ into B O₄⁻ units. The contribution of Li⁺ ions in the conduction process is much more than that due to small polarons. The conductivity of the glasses is mostly controlled by the Li⁺ ions concentration rather than the activation energy for CeO₂ > 5 mol%. Lower than 5 mol% CeO₂ the conductivity is controlled by both factors. The dependence of W on BO₄⁻ content supports the idea of ionic conduction in these glasses.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi₂O₃-P₂O₅ glass with low-P₂O₅ content (20-25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF₂. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF₂ substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s-6p interband transition in Bi³⁺ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.     

Spectroscopic investigation and optical characterization of novel highly thulium doped tellurite glasses

In this paper, optical properties of 75TeO₂-20ZnO-5Na₂O host glass doped with concentration of Tm³⁺ up to 10 %mol were studied in order to assess the most suitable rare earth content for short cavity fiber lasers. Raman spectroscopy revealed a change in the glass structure while increasing Tm³⁺ content, similar to the well known addition of alkali ions in a glass. Influence of the fabrication process on the OH⁻ content was determined by FTIR measurements. Refractive index of Tm³⁺ doped tellurite glasses was measured at five different wavelengths ranging from 533 nm to 1533 nm. Lifetime and emission spectra measurements of the Tm³⁺ doped tellurite glasses are reported.     

Broadband infrared luminescence of Ni-doped silicate glass-ceramics containing lithium aluminate spinel nanocrystals

Transparent Ni²⁺-doped SiO₂-Al₂O₃-Ga₂O₃-Li₂O (LGAS) glass-ceramics embedding lithium aluminate spinel nanocrystals was prepared. After heat treatment, LiAl₅O₈ crystallite was precipitated in the glasses, and its size was about 3 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-made glass to the octahedral sites in the glass-ceramics. Upon excitation at 980 nm, broadband infrared luminescence centered at around 1250 nm with full width at half maximum (FWHM) more than 250 nm was observed originating from the ³T₂(³F) → ³A₂(³F) transition of Ni²⁺ in octahedral sites. The broadband near-infrared (NIR) emission from Ni²⁺-doped glass-ceramics can be as host materials for broadband optical amplifier.     

Local field dependent fluorescence properties of Eu ions in a fluorometaphosphate laser glass

A fluorometaphosphate laser glass doped with Eu³⁺ ions has been synthesized and studied by broad band optical spectroscopy and time-resolved fluorescence line narrowing techniques in order to explore the local field dependent fluorescence properties of the lanthanide ions in this host. From the Raman and the vibronic spectra, various structural phosphate groups coupled to the Eu³⁺ ions have been identified. Local field dependent ⁵D₀ → ⁷F_J (J = 0-6) emission spectra and the lifetimes of the ⁵D₀ level have been measured under resonant excitation of the Eu³⁺ ions at different wavelengths within the ⁷F₀ → ⁵D₀ band at 16 K. From these data and using the Stark level positions of the ⁷F₁ and ⁷F₂ multiplets, a crystal-field analysis has been carried out assuming a C_2v orthorhombic local symmetry. The radiative Judd-Ofelt parameters have been calculated for the different local fields found in the glass and their relative variation has been discussed. The results obtained suggest the existence of a relatively narrow distribution of local fields generated by successive distortions of a unique kind of site for all the Eu³⁺ ions in this fluorometaphosphate glass.     

Temperature Dependence of the Absorption Spectra and Optical Parameters in TGS and Cu2+-Doped TGS Crystals

The effect of temperature on the optical absorption spectra and optical parameters is investigated for pure TGS and TGS doped with Cu²⁺ ions. Absorption measurements cover the range from room temperature to about 355 K in the energy range 3-5.5 eV. The temperature dependence of the band gap E_g(T) reveals an anomaly at the phase transition temperature for both pure and Cu²⁺-doped TGS crystals. In the region of the absorption edge the absorption coefficient is found to display Urbach-rule behaviour. The characteristic Urbach parameters are determined and their temperature dependence is investigated.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.     

Role of nickel ion coordination on spectroscopic and dielectric properties of ZnF2-As2O3-TeO2:NiO glass system

20ZnF₂-30As₂O₃-(50 − x)TeO₂:xNiO (0 ≤ x ≤ 2.0) glasses were synthesized. The glasses were characterized by X-ray diffraction, scanning electron microscopy, EDS and DSC techniques. A variety of properties, i.e. optical absorption, infrared, magnetic susceptibilities and dielectric properties (constant ?′, loss tan δ, a.c. conductivity σ_ac over a wide range of frequency and temperature) of these glasses have been carried out. The analysis of results of all these studies has indicated that the nickel ions occupy both octahedral and tetrahedral positions and the gradual increase of NiO content in the glass matrix causes growing proportions of Ni²⁺ ions that occupy octahedral positions. The luminescence spectra of these glasses have exhibited a broad emission band in region 1200-1450 nm identified due to ³T₂(3F) → ³A₂(3F) octahedral transition of Ni²⁺ ions. The luminescence efficiency and cross section have been found to be the highest for the glass containing highest concentration of NiO. Finally it is concluded that the higher the concentration of octahedrally positioned Ni²⁺ ions, the higher is the luminescence efficiency.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Optical basicity, interpreted by means of Ce 5d level spectroscopy in ionic crystals

The concept of optical basicity based on spectroscopy of Tl⁺, Pb²⁺, and Bi³⁺ energy levels in oxidic media like glasses and molten salts will be tested against information and theoretical knowledge available on Ce³⁺ in oxide ionic crystals. The redshift of the 4f → 5d transition of Ce³⁺ does not provide a basis for determining optical basicity. It will be shown that the proper basis is provided by the shift of the whole 5d configuration. Reasons why optical basicity can be based on the redshift of the ¹S₀ → ³P₁ transition in Tl⁺, Pb²⁺, and Bi³⁺ will be discussed. The theory on the centroid shift in Ce³⁺ provides new insights in the relation between optical basicity and physical properties like anion polarizability and refractive index. An alternative method to calculate optical basicity from the chemical composition of a compound will be proposed both for oxide and fluoride compounds.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Deep-UV Raman spectroscopic analysis of structure and dissolution rates of silica-rich sodium borosilicate glasses

As part of ongoing studies to evaluate relationships between structure and rates of dissolution of silicate glasses in aqueous media, sodium borosilicate glasses of composition Na₂O·xB₂O₃·(3 − x)SiO₂, with x ≤ 1 (Na₂O/B₂O₃ ratio ≥ 1), were analyzed using deep-UV Raman spectroscopy. Results were quantified in terms of the fraction of SiO₄ tetrahedra with one non-bridging oxygen (Q³) and then correlated with Na₂O and B₂O₃ content. The Q³ fraction was found to increase with increasing Na₂O content, in agreement with studies on related glasses, and, as long as the value of x was not too high, this contributed to higher rates of dissolution in single pass flow-through testing. In contrast, dissolution rates were less strongly determined by the Q³ fraction when the value of x was near unity, and appeared to grow larger upon further reduction of the Q³ fraction. Results were interpreted to indicate the increasingly important role of network hydrolysis in the glass dissolution mechanism as the BO₄ tetrahedron replaces the Q³ unit as the charge-compensating structure for Na⁺ ions. Finally, the use of deep-UV Raman spectroscopy was found to be advantageous in studying finely powdered glasses in cases where visible Raman spectroscopy suffered from weak Raman scattering and fluorescence interference.