Optical absorption and emission properties of Pr and Er in lithium cesium mixed alkali borate glasses

This article presents the optical absorption and emission properties of Pr³⁺ and Er³⁺ in mixed alkali borate glasses of the type 68B₂O₃·xLi₂O·(32-x)Cs₂O (where x=8, 12, 16, 20 and 24). The variation of Judd-Ofelt intensity parameters (Ω_λ), the peak wavelength of the hypersensitive transitions, radiative transition probabilities (A_rad) and peak emission cross-sections (σ_p) with x in the glass matrix have been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes (τ_R) of certain excited states of both Pr³⁺ and Er³⁺ in lithium cesium mixed alkali borate glasses are reported. Branching ratios (β) and integrated absorption cross-sections (Σ) for certain important transitions are presented. Peak stimulated emission cross-sections (σ_p) are calculated for the observed emission peaks of Pr³⁺ and Er³⁺ ions in this glass matrix.     

Structural and optical properties of lithium borobismuthate glasses

Glasses with compositions 25Li₂O-(75−x)Bi₂O₃-x B₂O₃, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap E_g^opt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion α_o²⁻ and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B₂O₃ content have been analyzed and discussed in terms of the changes in the glass structure.     

Thermal properties and structures of chlorocadmate, bromocadmate, and bromochlorocadmate glasses

Glass transition temperatures (T_g), crystallization temperatures (T_x), and ¹¹³Cd magic-angle spinning (MAS) NMR spectra of the chlorocadmate, bromocadmate, and bromochlorocadmate glasses and the CdCl₂, CdBrCl, and CdBr₂ crystals have been measured. The T_g and T_x, and thermal stabilities (T_x−T_g) decreased with increasing Br-content. No enhancement of (T_x−T_g) of bromochlorocadmate glasses by anion-mixing was observed. The CdCl₂ and CdBr₂ crystals gave the isotropic chemical shifts of 183 and −24 ppm, which are assigned to the CdCl₆ and CdBr₆ octahedra, respectively. The isotropic chemical shifts of CdBrCl crystal (186, 166, 135, 101, 63, 25 and −21 ppm) were assigned to CdBr_nCl_(6−n) (n=0-6) octahedra, respectively. It was found that the Br and Cl atoms in CdBrCl randomly occupy chlorine sites in the CdCl₂ structure. The ¹¹³Cd MAS NMR spectra revealed that the chlorocadmate, bromocadmate, and bromochlorocadmate glasses are composed of the CdCl₆, CdBr₆ and CdBr_nCl_(6−n) octahedra (n=0-6), respectively, and that the Cd²⁺ in all the bromochlorocadmate glasses was more preferentially bonded to Br⁻ than Cl⁻. The relationship between the thermal properties and the anion coordination environments around Cd²⁺ in these glasses is discussed.     

Local atomic structures in Zr-Ni metallic glasses

Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr₆₄Ni₃₆ metallic glass consist of Zr₂Ni-like and ZrNi-like CSROs.     

Characterization and electrical properties of V2O5-CuO-P2O5 glasses

Characterization and electrical properties of vanadium-copper-phosphate glasses of compositions xV₂O₅-(40−x)CuO-60P₂O₅ have been reported. X-ray diffraction (XRD) confirms the amorphous nature of these glasses. It was observed that, the density (d) decreases gradually while the molar volume (V_m) increases with the increase of the vanadium oxide content in such glasses. This may be due to the effect of the polarizing power strength, PPS, which is a measure of ratio of the cation valance to its diameter. The dc conductivity increases while the activation energy decreases with the increase of the V₂O₅ content. The dc conductivity in the present glasses is electronic and depends strongly upon the average distance, R, between the vanadium ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron.     

Molecular dynamics simulation of ternary glasses Li2O-P2O5-LiCl

Molecular dynamics simulation of binary glass 52Li₂O-48P₂O₅ and ternary glasses 45Li₂O-42P₂O₅-13LiCl and 39Li₂O-36P₂O₅-25LiCl was undertaken to study the effects of the addition of LiCl to the binary phosphate glass. The results show that addition of LiCl in the glass creates more non-bridging oxygens and reduces P-O-P chain lengths and branches in these chains, leading to a weakening of the glass matrix and consequent lowering of T_g. Interchain linkages mediated by Li in the binary structure diminish, and consequently better channels are created for Li⁺ movement, enhancing the ionic conductivity σ. Structure parameters also indicate the absence of LiCl clusters in the glass matrix.     

Optical absorption and thermoluminescence properties of ZnF2-MO-TeO2 (MO=As2O3, Bi2O3 and P2O5) glasses doped with chromium ions

Optical absorption, thermoluminescence, infrared spectra and differential thermal analysis of three different tellurite glass systems viz., ZnF₂-As₂O₃-TeO₂, ZnF₂-Bi₂O₃-TeO₂ and ZnF₂-P₂O₅-TeO₂ containing 0.4% of Cr₂O₃, have been investigated. Results have been analysed in the light of different oxidation states of chromium ion and the most suitable host for lasing Cr³⁺ ions has been identified and reported.     

Phase separation and partial devitrification in soda-lime silicate glasses

2 O-rich droplets dispersed throughout the SiO₂-rich matrix and nanoparticles of metallic silver. In exchanged specimens the joint effect of colloidal silver and electric field results in partial transformation of the amorphous droplets into crystalline Na₂O particles. Received: 11 February 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

Enhancing fluorescence emission properties of Dy doped in chalcogenide glass via very small compositional modifications

It has been experimentally confirmed that the addition of very small amount, tantamount to ∼1 mol%, of the group III elements (Ga or In) in combination with alkali halides (CsBr or RbBr) into chalcogenide Ge-As-S glass significantly improves the emission properties of Dy³⁺ dopant. Preferential location of Br in the first coordination shell of Dy³⁺, which occurs spontaneously during the vitrification process, is proposed to make Dy³⁺ experience different crystal fields, reduced phonon energy and modified local refractive index. This restructuring effect as a result of such minute compositional adjustments thus enhances the optical properties of rare earth elements embedded in chalcogenide glasses, while keeping their thermal properties unaltered.     

Structural and electrical properties of iron molybdenum phosphate glasses

Summary  Iron molybdenum phosphate glasses [xMoO₃ · (0.6 -x)P₂O₅ · 0.4Li₂O] :yFe₂O₃ with 0 ≤x ≤ 0.6 andy = 0.03 (mol%) prepared in ambient atmosphere using the melt quenching technique were studied by using DC electrical conductivity,⁵⁷Fe M?ssbauer and infrared spectroscopies. The DC conductivity depends on the MoO₃ concentrationx. It was observed that, with increasingx, the ratio Fe²⁺ /(Fe³⁺ + Fe²⁺) and the DC conductivity increase. Infrared spectroscopy and X-ray powder diffraction indicate that a Li₂ MoO₄ crystalline phase is present for high MoO₃ content samples (x = 0.5, 0.6). This work was partly sponsored by FINEP, CNPq (Brazilian agencies) and UECE (Universidade Estadual do Cearà).     

Molar volume and compactness versus mean coordination number in GeSeFe glasses: observation of a threshold behavior

Molar volumes, V, and compactness values, α, of 34 glassy compositions of the GeSeFe system have been obtained using their measured densities. The property–composition dependences are examined in light of the models proposed for the structure of these network glasses. Received: 28 August 2000 / Accepted: 9 January 2001 / Published online: 23 March 2001     

Influence of borate content on the radiative properties of Nd ions in fluorophosphate glasses

Spectroscopic properties of Nd³⁺ in barium fluoroborophosphate glassy matrix have been analyzed by fitting the experimental data with the standard Judd-Ofelt theory. Various spectroscopic parameters viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross-sections and optical gain of the principal fluorescence transitions from the ⁴F_3/2 metastable level are obtained. Results show that addition of borate content to the fluorophosphate matrix will reduce the fluorescence spectral properties of Nd³⁺. However, the radiative properties of the present fluoroborophosphate glassy matrix are found to be well improved over that of pure borate and phosphate matrix and is attributed to the influence of fluorine content in the glassy matrix. The changes in the position and the Judd-Ofelt intensity parameters are correlated with the structural changes in the host glass matrix. The shift of the hypersensitive band shows that the covalency of the rare earth to oxygen bond increases with the increase of Na₂O content. This covalency effect and the formation of the BO₄ groups with the addition of Na₂O content are responsible for the increase in the radiative properties of the present system. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content was carried out and the results show that both are below the critical level for optimum laser performance.     

The effect of compositional variations on the glass-transition and crystallisation temperatures in Ge-Se-In glasses

The glass-transition (T_g) and crystallisation (T_x) temperatures of glassy Ge_xSe_yIn₁₂ (7≤x≤28) have been determined from differential scanning calorimetry measurements. The variations of T_g and T_x with composition have been specified. It has been found that T_g reaches a maximum at 614 K for the composition Ge_23.33 Se_64.67 In₁₂ while T_x passes through a minimum at 740 K for the same composition. The values of the cohesive energies of the studied compositions have also been estimated using the chemical bond approach method. It is found that the composition Ge_23.33Se_64.67In₁₂ possesses the maximum cohesive energy. These results are explained in terms of the structure of Ge-Se-In glasses. Received: 12 March 2001 / Accepted: 29 March 2001 / Published online: 23 May 2001     

Microexplosions in tellurite glasses

Femtosecond laser pulses were used to produce localized damage in the bulk and near the surface of baseline, Al₂O₃-doped and La₂O₃-doped sodium tellurite glasses. Single or multiple laser pulses were non-linearly absorbed in the focal volume by the glass, leading to permanent changes in the material in the focal volume. These changes were caused by an explosive expansion of the ionized material in the focal volume into the surrounding material, i.e. a microexplosion. The writing of simple structures (periodic array of voxels, as well as lines) was demonstrated. The regions of microexplosion and writing were subsequently characterized using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and atomic force microscopy (AFM). Fingerprints of microexplosions (concentric lines within the region and a concentric ring outside the region), due to the shock wave generated during microexplosions, were evident. In the case of the baseline glass, no chemistry change was observed within the region of the microexplosion. However, Al₂O₃-doped and La₂O₃-doped glasses showed depletion of the dopant from the edge to the center of the region of the microexplosions, indicating a chemistry gradient within the regions. Interrogation of the bulk- and laser-treated regions using micro-Raman spectroscopy revealed no structural change due to the microexplosions and writing within these glasses. Received: 27 December 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. +1-509/376-3108, E-mail: sk.sundaram@pnl.gov     

XPS study on silica-bismuthate glasses and glass ceramics

X-ray photoelectron spectroscopy (XPS) was used to evidence the effect of the Bi₂O₃ to SiO₂ ratio and of partial crystallisation on the electronic charge density around the atoms entering silica-bismuthate glasses of nominal composition 0.01Fe₂O₃⋅0.99[xSiO₂⋅(100−x)Bi₂O₃] with . The core level spectra show significant composition dependent changes in binding energy, and the full width at half maximum of photoelectron peaks both of cations and of oxygen atoms. The analysis reveals changes in electron density correlated with the ionic and covalent character of the samples. The shift in binding energy suggests charge transfer from silicon and oxygen atoms to bismuth atoms. Contrary to the expected behaviour in conventional silicate oxide systems, the results indicate an increase of ionicity for silicon and of covalency for bismuth atoms. The same evolution of ionicity/covalency is observed after partial crystallisation.     

Ionic conductivity in borate glasses with three types of mixed alkali cations

We have investigated the temperature- and frequency-dependent ionic conductivity in (Li_0.67 ? xNa_0.33 Rb_x)₂B₄O₇ (LNRBO) glasses with x = 0, 0.07, 0.2, 0.33, 0.47, and 0.6. The mixed alkali effect of the ternary mixed alkali system LNRBO is compared with that of the binary mixed alkali systems (Li_1 ? xNa_x)₂B₄O₇ (LNBO), (Li_1 ? xRb_x)₂B₄O₇ (LRBO) and the single alkali glass Rb₂B₄O₇ (RBO). From the results of the dc conductivity and dc activation energy, we observe that the LNRBO system exhibits the combined characteristic of binary mixed alkali systems LNBO and LRBO. It is found that the power-law exponent n for binary alkali glass is the same as that for ternary alkali glass but it is lower than that for single alkali glass. This indicates that the dimensionality of conducting pathway in the mixed alkali glasses of LNBO, LRBO and LNRBO is lower than that in the single alkali RBO. We discuss the concentration dependence of the dc conductivity and dc activation energy in the framework of the bond valence technique to reverse Monte Carlo produced structural model [Phys. Rev. Lett. 90, 155507 (2003)].     

Short-range order changes induced by heat treatment in yttrium-aluminosilicate glasses

Short-range order and local atomic configuration in yttrium-aluminosilicate glasses doped with gadolinium were studied by infrared (IR) spectroscopy, ²⁷Al magic-angle-spinning nuclear magnetic resonance (MAS-NMR) and Gd³⁺ electron spin resonance (EPR) on as-prepared and heat-treated samples.A small amount of yttrium was replaced by gadolinium in the host glass because Y³⁺ and Gd³⁺ cations are quite similar and gadolinium ions can be used as structural sensor in electron paramagnetic resonance measurements. The results evidence weak changes in the structure of as-prepared glasses with respect to the coordination of aluminium atoms produced by gadolinium doping (0.2 and 0.5 mol%). New IR bands recorded from heat-treated samples are associated with stretching modes of hexacoordinated aluminium in AlO₆ octahedra. The effect of the heat treatment on aluminium environment is estimated by analysing the relative intensity of the component lines of simulated ²⁷Al MAS-NMR spectra. High-coordinated AlO_n species were identified in all samples. EPR results evidence the increase of the number of gadolinium sites with weak crystal field as effect of the structural relaxation.     

Study on the influence of TiO2 on the insulating strength of ZnO-ZnF2-B2O3 glasses by means of dielectric properties

ZnO-ZnF₂-B₂O₃ glasses containing small concentrations of TiO₂ ranging from 0 to 0.6 mol% were prepared. Dielectric properties (constant ε′, loss tan δ, ac conductivity σ_ac over a moderately wide range of frequency and temperature at room temperature in air medium) of these glasses have been studied. The results of these studies were analyzed with the aid of data on optical absorption, ESR and IR spectra of these glasses. The analysis suggests that when the concentration of TiO₂>0.2 mol%, the titanium ions, in addition to Ti⁴⁺ state, co-exist in Ti³⁺ state, act as modifiers and reduce the breakdown strength.     

Numerical studies of the vibrational isocoordinate rule in chalcogenide glasses

Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds. This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities of states. What is striking, however, is that, at a given average coordination, these properties are nevertheless almost independent of the elemental composition. Here, we report on some numerical verification of this experimental rule as applied to the vibrational density of states. We find that this rule is not exact but holds qualitatively well over a wide range of compositions and local chemical correlations. Received 25 April 2000     

Elastic properties and spectroscopic studies of lithium lead borate glasses

Elastic properties of xLi₂O — 20PbO — (80-x)B₂O₃ glasses have been measured at a frequency of 10 MHz using X-cut and Y-cut quartz transducers. The trends in the variation of elastic moduli, Poisson’s ratio and Debye temperature have been studied. The elastic moduli namely longitudinal and young’s modulus show strong linear dependence while bulk and shear modulus vary marginally as a function of Li₂O concentration. The Poisson’s ratio is found to be almost constant and Debye temperature increases with the increase of Li₂O concentration. IR, MAS-NMR and glass transition temperature studies have been also carried out. Glass transition temperature is found to increase with increase of Li₂O concentration. IR and MAS-NMR spectra show characteristic features of borate network and systematic change as a function of Li₂O concentration. The variation in the elastic properties and structural features of IR and MAS-NMR indicate that Pb²⁺ ions are likely to occupy network forming positions in this glass system. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.