Formation of nanoclusters through silver reduction in glasses: The model

The system of equations describing the formation of silver nanoclusters through the reduction of ionic silver in the course of thermal processing of silver containing glasses in hydrogen is formulated and solved numerically. The processes of the clusterization of neutral silver within the glass and at the surface, and the growth of the nanoclusters are modeled with the account of different mobilities and concentrations of the participating species. The influence of the variation of diffusion coefficients of Ag⁰ atoms, Ag⁺ and H⁺ ions as well as concentration of Ag⁺ ions in the glass matrix. It is shown that concentration distribution of neutral hydrogen (H⁰) strongly depends on the relationship between concentration of Ag⁺ ions (C_Ag⁺) and concentration of neutral hydrogen at the glass surface (C₁), as well as between diffusion coefficients of silver and hydrogen ions. When D_Ag⁺ ≪ D_H⁺ and C_Ag⁺ ≫ C₁, the total hydrogen concentration profile (C_Htot = C_H⁰ + C_H⁺) is defined by silver ion diffusion coefficient D_Ag⁺. Concentration of neutral silver, C_Ag⁰, represents a bell-shaped depth distribution, whose maximum moves to the depth linearly with t^1/2 with the rate depending both on the diffusion coefficient of neutral silver, D_Ag⁰, and neutral hydrogen, D_H⁰. It is shown that the depth position of the maximum coincides with the frontier of the layer filled by clusters. The kinetics of the cluster radius growth in the bulk of the glass also depends both on D_Ag⁰ and D_H⁰ and essentially deviated from the kinetic law R² ∼ t predicted earlier in the assumption of time-independent oversaturation. The kinetics of Ag cluster growth on the glass surface turned out independent of the D_Ag0 diffusion coefficient.     

Nano-composite soda lime silicate glass prepared using silver ion exchange

Commercial soda lime silicate glasses have been subjected to ion exchange at different temperatures ranging from 320 to 500 °C in a molten mixture of AgNO₃ and NaNO₃ with molar ratio of 10:90, 02:98 and 50:50 for different time periods ranging from 40 to 180 min. Optical and structural properties of the ion exchanged glass are measured using UV–Vis–NIR absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). Signature of silver nanoparticle formation is obtained from the UV–Vis–NIR spectra, which shows a peak at 425 nm due to surface plasmon resonance (SPR). Replacement of Na⁺ ions by Ag⁺ ions is inferred from FTIR spectra. Fluorescence spectra reveal the formation of Ag⁰ atoms from Ag⁺ ions at higher temperatures. TEM image shows the silver nanoparticles of average size 3.75 nm. At exchange temperature of 500 °C Ag nanoparticles are formed without post-exchange annealing treatment.     

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.     

EPR study in the SiO2 system

The EPR spectra of Fe³⁺ and V⁴⁺ ions, and radiation centres have been studied in α-tridimite. Consideration of the EPR data in all crystalline and vitreous forms of the SiO₂ system is made. It is shown that the crystal field strength and symmetry did not change considerably in different polymorphs of silica, the changes in hyperfine structure constants being significant. The relation between electronic structure of vitreous silica and different crystalline forms is established.     

A pulsed EPR study of clustering of Yb ions incorporated in GeO2 glass

The structural aspects of clustering of Yb³⁺ ions and the paramagnetic behavior of these clusters have been investigated in GeO₂ glasses doped with 140-1100 ppm by weight of Yb₂O₃ using time-domain electron paramagnetic resonance (EPR) spectroscopic techniques. The echo-detected EPR (EDEPR) spectra of Yb³⁺ ions and their unusual dependencies on microwave power and magnetic field have been found to be indicative of the formation of clusters of these rare earth ions in GeO₂ glass that behave as non-Kramers type spin systems. The magnetic field and concentration dependence of phase relaxation rates of Yb³⁺ in these glasses further substantiate such a scenario and indicate the formation of clusters of Yb³⁺ ions. A comparison of the EDEPR spectra with calculated cw-EPR line shapes yields a semi-quantitative measure of the typical cluster size of ?3 Yb atoms and intra-cluster Yb-Yb distances of 3.5-4.0 Å in these glasses at doping levels of ?350 ppm of Yb₂O₃.     

Magnetic resonance of the B2O3Na2OMoO3 vitreous system

The structure and properties of molybdenum-doped soda-borate glasses were studied by means of electron paramagnetic resonance as functions of the molybdenum oxide concentration in the range 1–25 mol% MoO₃, the keeping time of the samples at the preparation temperature in the range of 15–180 min, the preparation temperature in the range of 900–1300°C, and the soda-borate matrix composition in the range 0–34 mol% Na₂O.The EPR measurements gave evidence of the existence of three types of site for the Mo⁵⁺ ions, their relative fraction as well as the paramagnetic center density and the EPR lineshape symmetry being dependent on the above-mentioned factors. The evolution of the ¹¹B NMR lineshape in the studied samples also showed that the fourfold-coordinated boron atoms fraction is greatly influenced by the modification of these factors. The good agreement between the structural information obtained by ¹¹B NMR and Mo⁵⁺ EPR studies recommends the EPR spectra of Mo⁵⁺ ions as an excellent sensor for the structure of the borate glasses.     

EPR study of RLi2O.V2O5, RNa2O.V2O5, RCaO.V2O5, and RBaO.V2O5 modified vanadate glass systems

Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa₂O.V₂O₅ system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these lines exhibit dramatic narrowing as R approaches 0.5. In the model proposed here, this narrowing is due to an increase in hopping time for small polarons associated with V⁴⁺ ions in these systems. Increases in polaron hopping times are accompanied by increases in electron spin-spin relaxation times T₂'s, and, an associated narrowing of EPR linewidths. Experiments confirm that spectral widths are limited by electron T₂'s due to the fact that EPR linewidths do not vary with temperature down to 4.2 K. Resolved spectra in RNa₂O.V₂O₅ at R = 0.5 reveal a hyperfine coupling parameter of 0.0177 ± 0.0008 T, corresponding to an upper-limit polaron hopping frequency of 487 ± 20 MHz. By similar analyses, the systems of RCaO.V₂O₅, RBaO.V₂O₅, and RLi₂O.V₂O₅ exhibit comparable polaron hopping frequencies limits of 480 ± 20 MHz, 469 ± 20 MHz, and 468 ± 20 MHz, respectively, when R is near 1.0. In addition to the relaxation effects discussed here, results of modeling of resolved spectra to obtain hyperfine coupling constants A_|| and A_┴, and g_┴ values g_|| and g_┴ are presented and discussed.     

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.     

Up-conversion enhancement in Er3 +-Ag co-doped zinc tellurite glass: Effect of heat treatment

The melt quenching method was used to synthesize the Ag⁰ nanoparticles and Er^3 + ions co-doped zinc tellurite glass. The glasses were characterized by differential thermal analyzer, UV–VIS-IR absorption, photoluminescence spectroscopy and TEM imaging. Heat treatment at different annealing time intervals above the glass transition temperature was applied to reduce the Ag⁺ ions to Ag⁰ NPs. The influence of heat treatment on structural and optical properties is examined. Intense and broad up-conversion emissions of silver are recorded in the visible region. Up-conversion luminescence spectra revealed three major emission peaks at 520, 550 and 650 nm originating from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 levels, respectively. An efficient enhancement in visible region is observed for samples containing silver NPs. The absorption plasmon peaks are evidenced around 560 and 594 nm. The effect of localized surface plasmon resonance and the energy transfer from the surface of silver NP to trivalent erbium ions are described as the sources of enhancement.     

The investigation of the magnetic interaction between Cu2+ and V4+ ions in x(CuO·2V2O5)(1 − x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility measurements have been performed on (CuO·2V₂O₅)(1?x)[2B₂O₃·K_2O] glasses with 0 ? x ? 40 mol. %.For x < 10 mol.%, both Cu²⁺ and V⁴⁺ ions are present mostly as the isolated species. The values of MO coefficients indicate a high covalent degree of the transition metal (TM)-oxygen bonds. Also, the EPR parameters suggest the presence of strong (TM)-oxygen bonds along the 0_z axis, which lead to an octahedral (Oh) symmetry component at TM ions sites.In the case of 10 ? x ? 40 mol.%, the dipole-dipole and superexchange interactions occur between transition metal ions, which determine a broad resonance line at $\text{g ? 2}$. The strong interactions between Cu²⁺ and V⁴⁺ ions give rise to the exchange coupled Cu²⁺ V⁴⁺ pairs in the studied glasses with x > 10 mol.% (y > 3.9 mol.%).     

Electron trap centers in Ag-borate glasses

The center created by silver trapping an electron in borate glasses are considered. It is shown by ESR techniques that on trapping an electron, silver ions may form four types of centers: the single Ag⁰ or (Ag⁺ + e) centers, and, at higher Ag contents, the Ag⁰(Ag⁺) or (Ag⁺ + e) (Ag⁺) centers in which a second silver is involved. The formation and stability of these centers is critically dependent on the silver content, the concentration of alkali and the temperature of irradiation and measurement. The Ag⁰(Ag⁺) center is generally enhanced by increasing silver and decreasing alkali content and does not show separate signals for the two isotopes ¹⁰⁷Ag, ¹⁰⁹Ag because the two silvers in proximity occur in three different isotope combinations which are superimposed.Above 20% alkali the hyperfine splitting constant for the silver—electron trap center was found to decrease with increasing alkali content, probably in connection with the increasing appearances of non-bridging oxygens and the trapping of the electron in an oxygen vacancy in the vicinity of Ag⁺, i.e. a change from Ag⁰ to (Ag⁺ + e) center. A similar decrease was observed in high alkali (30% R₂O) glasses with changes of alkali from Li⁺ to K⁺.     

Electron spin resonance and magnetic studies on CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Room temperature electron spin resonance (ESR) spectra and temperature dependent magnetic susceptibility measurements have been performed to investigate the effect of iron ions in 41CaO · (52 − x)SiO₂ · 4P₂O₅ · xFe₂O₃ · 3Na₂O (2 ? x ? 10 mol%) glasses. The ESR spectra of the glass exhibited the absorptions centered at g ≈ 2.1 and g ≈ 4.3. The variation of the intensity and linewidth of these absorption lines with composition has been interpreted in terms of variation in the concentration of the Fe²⁺ and Fe³⁺ in the glass and the interaction between the iron ions. The magnetic susceptibility data were used to obtain information on the relative concentration and interaction between the iron ions in the glass.     

Study of color and structural changes in silver painted medieval glasses

Silver was introduced into medieval glass by an ancient painting process using different clay minerals (ochre, illitic, montmorillonitic, and kaolinitic clays). The colorimetric properties, studied by UV-Vis spectroscopy, were dependent on the clay mineral as a result of different concentration of Ag ions diffused into the glass surface. TEM results showed the well known formation of silver nanoclusters which give the yellow coloration of the glass. The obtained results showed that clay properties such as specific surface area, pore volume and iron concentration (Fe₂O₃), are important factors that affect the yellow coloration. It is also observed that Fe₂O₃ acts as an oxidant agent for silver atoms providing the Ag₂O formation. This oxide cannot diffuse into the glass structure and avoid the ion-exchanged process. After Ag ion diffusion some structural changes occur in the glass as it has been shown by Raman spectroscopy. It is observed that the diffusion process leads to depolymerization of the glass network as it is determined by analyzing the Qⁿ components of Raman spectra. Two Raman bands at 148 and 244 cm⁻¹ assigned to Ag-O bonds can be associated to the presence of Ag₂O on the glass painted surface.     

Synthesis and ammonia sensing property of Ag3CuS2 nanocages obtained from Cu7S4 18-facet hollow nanopolyhedra

Ag₃CuS₂ nanocages were successfully fabricated for the first time via a convenient ion-exchange route by Ag⁺ reacting with Cu₇S₄ 18-facet hollow nanopolyhedra. The average size and shell thickness of Ag₃CuS₂ nanocages were around 400 and 30 nm, respectively. Room-temperature response of Ag₃CuS₂ nanocages to ammonia was investigated by photoluminescence-type sensor. Sensing results suggested that these hollow-structured Ag₃CuS₂ exhibited better performances including higher sensitivity, shorter response and recovery time than their rod-shape counterparts. A possible hole trapping mechanism was proposed.     

The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.     

Ag diffusion in amorphous As50Se50 films studied by XPS

X-ray photoelectron spectroscopy and depth profile analysis were used to investigate the X-ray-induced silver photodiffusion into an amorphous As₅₀Se₅₀ thin film. At the initial stages of irradiation an induction period was observed while core level spectra analysis revealed the existence of a mixed As–Se–Ag interlayer between the metal and the chalcogenide matrix. It was found that during the induction period this interlayer is enriched in silver and the existing As–Se–Ag intermediate species are transformed to Ag–Se–Ag that form the metal source for the effective silver photodiffusion. With further irradiation photodiffusion proceeds by the disruption of Ag–Se bonds and the recombination of As atoms with Se to stable As–Se units. Ultimately, silver concentration reaches a plateau when the diffusion stops. A separated Ag₂Se phase on the film’s surface is identified at this stage. Depth profile analysis shows that silver has been homogenously diffused into the chalcogenide matrix and the Ag₂Se phase exists only at the top surface layers probably in the form of quasi-crystalline clusters that prohibit further Ag diffusion.     

Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

Silver sulfide based glasses (I). Glass forming regions,structure and ionic conduction of glasses in GeS2Ag2S and GeS2Ag2SAgI systems

Ag₂S forms with GeS₂ stable glasses over a wide range of compositions (0–55% Ag₂S mol%). In the same system, more complex glasses obtained by dissolving silver iodide have been synthesized with up to 50 mol% AgI.Raman spectra are presented and a vibrational assignment in terms of bridging and non-bridging sulfur has been made. The electrical conductivity of these glasses has been measured over a temperature range (?50°C? + 50°C) and for various compositions by the complex impedance diagram method. At 25°C, the conductivity reached a maximum value of 6 × 10^?3 Ω^?1 cm^?1. Whatever the glass used, the same limit value of conductivity $\text{(σ ? 10 su?2 Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) and activation energy ($\text{E}{}_{\mathrm{\sigma }}\text{? 0.25}\text{eV}$) are obtained for the highest content of silver iodide. A conduction mechanism is proposed.     

Structure and non-linear optical performance of TeO2-Nb2O5-ZnO glasses

The non-linear optical performance and structure of TeO₂-Nb₂O₅-ZnO glasses was investigated as a function of ZnO content. The third-order non-linear optical susceptibility (χ⁽³⁾) as measured by a Degenerate Four Wave Mixing (DFWM) method, initially increased with increasing ZnO content to about 8.2 × 10⁻¹³ esu for a glass containing 2.5 wt% ZnO, and then decreased to 5.9 × 10⁻¹³ esu as the ZnO content increased to 10 wt%. There was no noticeable change as the ZnO content increased from 10 to 15 wt%. The non-linear optical response time, which caused electron cloud deformation, was from 450 to 500 fs. The structure of these glasses as analyzed by Raman spectroscopy and FT-IR spectra, was affected by the addition of ZnO up to 5 wt%, when, it is believed, the Zn²⁺ ions occupied the interstitial positions in the glass network by replacing the Nb⁵⁺ ions. The replaced Nb⁵⁺ ions occupied the network forming positions as the Te⁴⁺ ions. Increasing ZnO > 5 wt% did not have any further effect on the glass structure.     

Optical spectroscopy of silver ion-exchanged As-doped glass

Soda-lime-silicate glass containing arsenic oxide and undoped soda-lime-silicate glass (blank) are prepared by melting from pure sand (iron concentration lower than 0.01 wt%). The effect of arsenic on the optical properties of the glass with and without silver ion exchange at 325 °C for various times is investigated by optical absorption and photoluminescence spectroscopy. Emission/excitation spectra of silver ion exchanged glass allow differentiation of three stages in the silver incorporation into the glass network. First and second stages are only observed in the undoped glass ion exchanged for short times. Such stages are associated with the presence of isolated Ag⁺-ions and Ag⁺-Ag⁺ pairs, respectively. The third stage appears in the undoped glass ion exchanged for times longer than 10 min and in the arsenic-doped glass even for exchange times as short as 1 min. Then, this stage is characterised by molecular mixed species formed with Ag⁺ and Ag⁰, which coexist with nanoparticles of metallic silver. The presence of those Ag⁰-aggregates gives a yellow colour to the glasses, which show the well-know absorption band at about 400 nm due to surface plasmon resonance.