Ions In Silicate Glasses Research Articles

Influence of Cerium oxide on the structural aspects of soda-lime aluminosilicate glasses synthesized by sol-gel route

Soda-lime aluminosilicate glasses containing different mole fractions of cerium oxide (1–10 mol.%) with a nominal composition 2xCeO2-45SiO2-15Al2O3-(20-x)Na2O-(20-x)CaO were successfully synthesized via sol-gel route. Structural and role of cerium addition were investigated via X-ray diffraction (XRD), Fourier transforms infrared (FT-IR), Raman spectroscopic, and Photoluminescence techniques. All investigated glasses show a broad diffraction band (amorphous halo) pointing to the long-range structural disorder and amorphous nature of the as-synthesized glass powder. Raman and Fourier transform infrared spectral data indicate that CeO2 plays a crucial role (network modifier) in the main soda-lime aluminosilicate network. The building groups were Qn retraced by a simple deconvolution analysis technique (DAT) and the exchange among Q3 and Q2 species can be described simply in terms of interchange in the former arrangements Si2O52− (Q3) → SiO32− (Q2), this exchange occurs with high concentrations of cerium oxide in glasses matrix. Undoped and doped soda-lime aluminosilicate photoluminescence characteristics were analyzed. PL spectrum of the undoped sample reveals significant bands caused by Na, Ca, and Al ions in silicate glasses; once the doped cerium ion was added to the glasses, two bands formed at 690 and 538 nm, which are attributed to the well-known 5d-4f cerium emission band. Computational density functional theory (DFT) was applied for a single building block of the glass network using Becke three-parameter hybrid functional (B3LYP) correlation adopting the electron core potential basis set (3-21G) was used.

Temperature dependence of spectroscopic properties and energy transfer in Nd3+/Yb3+ co-doped silicate glass

In this work, we explore detailed energy transfer processes between Nd3+ and Yb3+ ions in silicate glasses. The absorption, temperature dependent emission spectra and decays of Yb3+ and Nd3+ singly doped and Nd3+/Yb3+ co-doped silicate glasses were measured and analyzed. The phonon assisted Nd3+→Yb3+ energy transfer was investigated. The phonons of 621 cm−1 and 1090 cm−1 contributing greatly to accelerate the energy transfer Nd3+ → Yb3+ and Yb3+ → Nd3+, respectively. The energy transfer efficiencies between Yb3+ and Nd3+ ions were theoretically and experimentally studied. We find that the cumulative time decreased with increasing temperature for Nd3+→Yb3+, whereas the cumulative time peaked at 350 K for Yb3+→Nd3+. We report increased energy transfer efficiencies of Nd3+→Yb3+ (73.19–82.31%) and Yb3+→Nd3+ (9.97–18.11%) with increasing temperature implying Nd3+ and Yb3+ co-doped silicate glass may be a promising candidate for efficient temperature sensors.

Photodarkening mechanisms of Pr3+ singly doped and Pr3+/Ce3+ co‐doped silicate glasses and fibers

AbstractIn this work, we revealed the possible mechanisms of the photodarkening in Pr3+ ions singly doped and Pr3+/Ce3+ co‐doped silicate glasses and fibers induced by X‐ray and 488‐nm laser radiations and studied the role of Ce3+ in increasing radiation resistance in Pr3+‐doped silicate glasses and fibers. The absorption, emission, electron paramagnetic resonance (EPR), radiation induced attenuation spectra, and X‐ray photoelectron spectroscopy (XPS) of Pr3+ singly doped and Pr3+/Ce3+ co‐doped silicate glasses before and after X‐ray radiation were measured and analyzed. The fluorescence intensity and photoinduced attenuation of Pr3+ singly doped and Pr3+/Ce3+ co‐doped silicate fibers at visible wavelengths pumped by 488‐nm laser were measured and analyzed. The influence of Ce3+ ions co‐doping on the spectroscopic properties of Pr3+ ions as well as the radiation‐induced defects in silicate glasses was studied. Results demonstrate that both X‐ray and 488‐nm laser radiations will induce photodamage in Pr3+ ions‐doped silicate glasses and fibers. Co‐doping Ce3+ (by up to 1 mol%) is efficient to suppress the darkening induced by both X‐ray and 488‐nm laser radiations without influence on the luminescence behavior of Pr3+ ions in silicate glasses and fibers. Our studies demonstrate the promising potential of Pr3+/Ce3+ co‐doped silicate glasses for visible lasing applications.

Investigation of the Incorporation of Cerium Ions in MCVD-Silica Glass Preforms for Remote Optical Fiber Radiation Dosimetry.

The incorporation of Ce3+ ions in silicate glasses is a crucial issue for luminescence-based sensing applications. In this article, we report on silica glass preforms doped with cerium ions fabricated by modified chemical vapor deposition (MCVD) under different atmospheres in order to favor the Ce3+ oxidation state. Structural analysis and photophysical investigations are performed on the obtained glass rods. The preform fabricated under reducing atmosphere presents the highest photoluminescence (PL) quantum yield (QY). This preform drawn into a 125 µm-optical fiber, with a Ce-doped core diameter of about 40 µm, is characterized to confirm the presence of Ce3+ ions inside this optical fiber core. The fiber is then tested in an all-fibered X-ray dosimeter configuration. We demonstrate that this fiber allows the remote monitoring of the X-ray dose rate (flux) through a radioluminescence (RL) signal generated around 460 nm. The response dependence of RL versus dose rate exhibits a linear behavior over five decades, at least from 330 µGy(SiO2)/s up to 22.6 Gy(SiO2)/s. These results attest the potentialities of the MCVD-made Ce-doped material, obtained under reducing atmosphere, for real-time remote ionizing radiation dosimetry.

Growth of Al2O3 films on chemically strengthened glass substrates by different deposition techniques

The exchange of small sodium ions in silicate glass by larger potassium ions from a molten salt bath below Tg produces a compressive stress on the glass surface region, which results in glass strengthening. The effects of thin film nucleation and initial growth on high stress and potassium-rich property of chemically strengthened glass substrates were investigated. Al2O3 thin films were prepared on chemically strengthened glass substrates by electron beam evaporation with ion beam assisted deposition and magnetron sputtering, respectively. The crystalline structure and morphology of Al2O3 thin films were studied by grazing incident X-ray diffraction and field emission scanning electron microscopy. The concentration distributions of potassium, aluminum and oxygen elements near the Al2O3 film/chemically strengthened glass interface were analyzed by electron probe micro-analyser. It is shown that Al2O3 films deposited on chemically strengthened glass substrates by different deposition techniques have an amorphous structure. Potassium ions outward diffusion from the chemically strengthened glass substrates are accompanied by aluminum and oxygen ions inward diffusion from the Al2O3 thin films into glass during deposition. Diffusion rates of potassium, aluminum and oxygen ions are very different using different deposition techniques. Compared with the chemically strengthened glasses, the surface compressive stress and the depth of the compressive layer in the chemically strengthened glasses deposited Al2O3 films decrease variously. The results show that the change of chemical composition throughout glass surface region in the Al2O3 thin films deposition process can cause a change in physico-chemical and mechanical properties of chemically strengthened glasses.

Features of the optical properties of diffusion layers obtained by successive replacement of sodium ions with copper and silver ions in silicate glass

It is experimentally shown that, when copper and silver ions are successively incorporated into silicate glass by the method of ion exchange, followed by heat treatment, metallic nanoparticles whose structure and composition depend on its temperature are formed in the glass. When the heat-treatment temperature is lower than the glass-transition temperature, spherical nanoparticles of silver and copper are formed in the glass; when the temperature is above the glass-transition temperature, nanostructures are formed that consist of a copper core and a silver shell. The absorption spectra of such structures are compared with the calculated spectrum of their absorption cross section.

Field-driven diffusion of transition metal and rare-earth ions in silicate glasses

The growing applications of glass-based photonic devices, like light waveguides and luminescent materials, demand the development of a versatile diffusion technique. Field-assisted solid-state ion diffusion is a novel technique developed for diffusing transition metal and rare-earth ions in silicate glasses. Due to the limitations of other conventional ion diffusion techniques in the case of multivalent ion diffusion, this technique serves to be equally suitable for the diffusion of both the monovalent and multivalent ions in the glass. In order to understand the mechanism of diffusion, thin films of Au/Er were deposited on soda-lime and borosilicate glass slides, and diffusion was established by applying an external electric field across the sample inside a furnace at a constant temperature. Alkali content of the glass was observed to deplete and the resulting vacancies were filled by the ions from the deposited film. The in-depth diffusion profiles of the doped-glasses were studied using secondary ion mass spectrometry and quantitative analysis was performed with Rutherford backscattering spectrometry. The optical absorption spectroscopy confirmed that the dopants were in non-precipitated form and transmission electron microscopy enabled direct observation of the size and distribution of the doped nanoparticles. The present results demonstrate that the diffusion depends on the processing conditions, glass composition and oxidation rate of the deposited film at the film–glass interface. The observed higher dopant concentration in the soda-lime silicate glass than the borosilicate glass may be due to the higher alkali content in the former glass. The diffusion of considerable amounts of Er content into the superficial layer of the glass, makes it suitable for telecommunication applications.

Selective behaviour of dilute Fe3 + ions in silicate glasses: an Fe K-edge EXAFS and XANES study

Iron K-edge EXAFS and XANES have been used to study the local structural environment of dilute quantities (0.2mol% Fe2O3) of Fe3+ in seven representative SiO2–R2O–R’O glasses where R=(Li, Na, K), R’=(Mg, Ca, Sr, Ba). Sample preparation was carried out by adding excess CeO2 as an oxidising agent and it was confirmed by optical absorption spectroscopy that iron was fully oxidised to Fe3+. This methodology has made possible, for the first time, an unambiguous EXAFS study of the coordination and local structural environment of dilute levels of Fe3+ in alkali–alkaline earth–silica glasses without the complications presented by the presence of Fe in multiple oxidation states. Coordination of Fe3+ in these glasses is strongly affected by the nature of the alkali and alkaline earth cations, with Fe3+–O CN increasing from 4.0±0.4 to 6.2±0.9 with decreasing alkali/alkaline earth ionic radius ratio (IRR). Respective FeO bond lengths of 1.87±0.01Å to 1.92±0.01Å were also obtained. Dilute Fe3+ in the studied glasses displays selective behaviour, as demonstrated by the opposing effects of alkali and alkaline earth ions on measured Fe3+ CN and Fe3+O bond length.

∼2 μm fluorescence radiative dynamics and energy transfer between Er3+ and Tm3+ ions in silicate glass

A Er3+/Tm3+ co-doped silicate glass with good thermal stability is prepared by melt-quenching method. An efficient emission of ∼2μm is observed under different selective laser excitations. The optical absorption and transmission spectra, Raman spectra, and emission spectra are tested to characterize ∼2μm emission properties of Er3+/Tm3+ co-doped silicate glasses and a reasonable energy transfer mechanism of ∼2μm emission between Er3+ and Tm3+ ions is proposed. Based on the optical absorption spectra, the Judd–Ofelt parameters and radiative properties were calculated. Intense ∼2μm emission is obtained from Er3+/Tm3+ co-doped silicate glasses due to the efficient energy transfer from Er3+ to Tm3+ ions. The energy transfer coefficient from Er3+ to Tm3+ ions can reach as high as 13.39×10−40cm6/s. In addition, the population of the OH groups is decreased and the ∼2μm emission is effectively enhanced with fluoride introduction. The emission property, together with good thermal property, indicates that Er3+/Tm3+ co-doped silicate glass is a potential kind of laser glass for efficient ∼2μm laser.

Improvement of radiation resistance by introducing CeO2 in Yb-doped silicate glasses

The influences of Ce on the radiation resistance of Yb-doped aluminosilicate glasses were investigated. The Ce ions in silicate glasses can effectively trap holes and free electrons due to their multivalency, consequently suppressing the radiation-induced absorption band. This could greatly improve the radiation resistance without obvious impact on the absorption properties of Yb-doped glasses. However, the fluorescence intensity and lifetime of Yb3+ ions were significantly decreased by high concentration Ce codoping. The mechanisms involved in these effects have also been discussed. The experiment results indicate that Yb-codoped glasses with a moderate Ce-concentration can be used as active medias for radiation–resistant materials in harsh radiation environments.

Synthesis and characterization of Ce 3+ doped silica (SiO 2) nanoparticles

A series of silica doped with different mol percentages of Ce 3+ concentration was synthesized using a sol–gel method to determine the dependence of photoluminescence wavelengths and intensity on the concentrations of the dopants. Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Rare-earths (REs) are insoluble in silica; due to this insolubility RE ions in silicate glasses enter as network modifiers and compete for non-bridging oxygen in order to complete their coordination. The morphological, structural, thermal and optical properties of the phosphors were characterized by X-ray diffraction, scanning electron microscopy, UV–vis absorption, photoluminescence, thermogravimetric analyses and differential scanning calorimeter. Silica (SiO 2) gel containing Ce 3+ ions was sputter coated with Au (gold) in order to monitor surface morphology of the samples. The highest emission intensity was found for the sample with a composition of 0.5 mol% Ce 3+. Cerium doped silica glasses had broad blue emission corresponding to the 2D 3/2– 2F J transition at 448 nm but exhibited apparent concentration quenching above concentrations of 0.5 mol% Ce 3+.

Sodium reconstruction on surface of silicate glasses in transmission electron microscope

We find that irradiated Na ions in silicate glasses undergo reconstruction on the surfaces before being repelled from the irradiated area by electron excitations. These results are based on evidence from time-dependent electron energy-loss spectroscopy. The process of reconstruction involves an irreversible change of the Na+→Na0→Na+, in which the initial and final Na+ ions have different bonding environments. The phenomenon is the result of the elimination of nonbridging oxygen associated with Na.

Rare earth ion distribution in sol–gel silicate glasses

Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Due to their relative insolubility in silica, rare earth (RE) ions in silicate glasses enter as network modifiers and compete for non-bridging oxygens in order to complete their coordination. Energy transfer between Tb 3+ ions is used here to study the distribution of RE ions in these porous glasses. The non-exponential decay of the 5D 3 fluorescence is due to cross relaxation. Using a model for energy transfer in fractional dimensions and fitting the decay profile to a stretched exponential, the number of nearby Tb 3+ ions and the dimensionality of the Tb 3+ ions in the pores could be determined. Analysis indicates that the observed fluorescence originates from relatively isolated ions. Samples annealed below 950 °C exhibit a dimensionality of ∼1.2.

Formation of nanoclusters in silver-doped glasses in wet atmosphere

Thermal stability of silver ions in silicate glasses in dry and wet (0.5 - 50% of water content) atmosphere under elevated (160–230 °C) temperature is studied. The glass is doped with silver using silver-to-sodium ion exchange procedure conventionally used for the formation of optical waveguides. It is found that the isothermal annealing of glasses doped with Ag+ ions in a wet argon atmosphere leads to the reduction of silver to metallic state and to the formation of silver nanoclusters in the glass body. The clustering in the course of water diffusion into the glass was studied by optical spectrometry. The clusters were not formed during annealing in a dry atmosphere at the same temperatures.

Cation diffusion and ionic conductivity in soda-lime silicate glasses

We have studied the mobilities of calcium and sodium ions in silicate glasses of compositions xNa2O (3 - x)CaO x 4SiO2 with x = 0.0, 0.1, 0.3, 1.0 and 3.0 by means of radiotracer diffusion, electrical conductivity measurements, and dynamic mechanical thermal analyses. In glasses containing sodium oxide, the Na+ ions are much more mobile than the Ca2+ ions, and are, therefore, governing the electrical conductivity. In the pure calcium silicate glass, the activation energy of Ca2+ diffusion is higher than the activation energy of the electrical conductivity. This provides strong evidence that the electrical conductivity of this glass is not determined by the migration of Ca2+ ions, but by impurity charge carriers, which are most likely Na+ ions. We sketch the composition-dependent mobilities of Na+ and Ca2+ ions in soda-lime silicate glasses with variable Na2O and CaO content. Our results indicate that the coordination environment of Ca2+ ions remains unchanged when CaO is replaced by Na2O which is consistent with recent results of molecular dynamic simulations. Moreover, our results confirm the formation of dissimilar Na-Ca pairs which lead to a non-random mixing of the cations in the glass. The formation of such pairs was recently deduced from nuclear magnetic resonance spectra of soda-lime silicate glasses.

Emission of Er- and Si-doped silicate glass films obtained by magnetron co-sputtering

Thin films of silicate glass containing Si excess and Er ions were fabricated by magnetron co-sputtering technique before being annealed at 450 °C to precipitate the Si excess in Si nanoclusters. The structural features were examined by infrared (IR) absorption spectroscopy, X-ray diffraction and transmission electron microscopy, while the emission properties were examined by photoluminescence (PL) spectroscopy. The evolution of the PL spectra obtained with both resonant (488 nm) and non resonant (476.5 nm) excitation lines, shows evidence of an important enhancement of the 1.54 μm signal when the Er ions coexist with Si nanoclusters (Si-nc), even though these latter appear non crystallized. Such results represent the first evidence of energy transfer from Si-nc to Er ions in silicate glass, and recall strikingly the similar process observed so far for the counterpart Si-rich SiO 2:Er films.

On the mobility of alkaline earth ions in mixed alkali alkaline earth silicate glasses

Activation energies of the diffusion of alkaline earth ions in silicate glasses of the composition A 2O 2BO 4SiO 2 have been compiled recently, where A is an alkali and B an alkaline earth metal. A pronounced dependence on the ratio r B/ r A of radii of alkaline earth ions B 2+ and alkali ions A + has been detected. A minimum occurs at a ratio of unity and the increase of the activation energies is much steeper for r B/ r A<1 when compared with the one for r B/ r A>1. This size effect of alkaline earth mobility can be explained qualitatively and quantitatively by a model of the mixed alkali effect, where the ionic mobility is affected by both a distribution of site energies and the packing density of oxygen.

The distribution of sodium ions in aluminosilicate glasses: a high-field Na-23 MAS and 3Q MAS NMR study

The local configurations around sodium ions in silicate glasses and melts and their distributions have strong implications for the dynamic and static properties of melts and thus may play important roles in magmatic processes. The quantification of distributions among charge-balancing cations, including Na + in aluminosilicate glasses and melts, however, remains a difficult problem that is relevant to high-temperature geochemistry as well as glass science. Here, we explore the local environment around Na + in charge-balanced aluminosilicate glasses (the NaAlO 2-SiO 2 join) and its distribution using 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at varying magnetic fields of 9.4, 14.1, and 18.8 T, as well as triple-quantum (3Q)MAS NMR spectroscopy at 9.4 T, to achieve better understanding of the extent of disorder around this cation. We quantify the extent of this disorder in terms of changes in Na-O distance ( d[Na-O]) distributions with composition and present a structural model favoring a somewhat ordered Na distribution, called a “perturbed” Na distribution model. The peak position in 23Na MAS spectra of aluminosilicate glasses moves toward lower frequencies with increasing Si/Al ratios, implying that the average d(Na-O) increases with increasing R. The peak width is significantly reduced at higher fields (14.1 and 18.8 T) because of the reduced effect of second-order quadrupolar interaction, and 23Na MAS NMR spectra thus provide relatively directly the Na chemical shift distribution and changes in atomic environment with composition. Chemical shift distributions obtained from 23Na 3Q MAS spectra are consistent with MAS NMR data, in which deshielding decreases with R. The average distances between Na and the three types of bridging oxygens (BOs) (Na-{Al-O-Al}, Na-{Si-O-Al}, and Na-{Si-O-Si}) were obtained from the correlation between d(Na-O) and isotropic chemical shift. The calculated d(Na-{Al-O-Al}) of 2.52 Å is shorter than the d(Na-{Si-O-Si}) of 2.81 Å, and d(Na-{Al-O-Al}) shows a much narrower distribution than the other types of BOs. 23Na chemical shifts in binary (Al-free) sodium silicate glasses are more deshielded and have ranges distinct from those of aluminosilicate glasses, implying that d(Na-NBO) (nonbridging oxygen) is shorter than d(Na-BO) and that d(Na-{Si-O-Si}) in binary silicates can be shorter than that in aluminosilicate glasses. The results given here demonstrate that high-field 23Na NMR is an effective probe of the Na + environment, providing not only average structural information but also chemically and topologically distinct chemical shift ranges (distributions) and their variation with composition and their effects on static and dynamic properties.

Optical absorption and fluorescent behaviour of titanium ions in silicate glasses

Titanium in normal melting conditions in air atmosphere present as Ti4+ ion in basic silicate glasses exhibited an ultra-violet cut-off in silicate glasses, viz. soda-magnesia-silica, soda-magnesia-lime-silica and soda-lime-silica glasses. This indicates that Ti4+ ion can be a good replacement for Ce4+ ion in producing UV-absorbing silicate glasses for commercial applications. The wavelength maxima at which the infinite absorption takes place in glasses was found to be around 310 nm against Ti-free blank glass in UV-region. The mechanism of electronic transition from O2- ligands to Ti4+ ion was suggested as L→ M charge transfer. The low energy tails of the ultra-violet cut-off were found to obey Urbach’s rule in the optical range 360–500 nm. The fluorescence spectra of these glasses were also studied and based on the radiative fluorescent properties it was suggested that the soda-lime-silica glass containing Ti4+ ion with greater emission cross-section would emit a better fluorescence than the corresponding soda-magnesia-lime-silica and sodamagnesia-silica glasses. The shift of emission wavelengths maxima towards longer wavelength in titania introduced silicate glasses was observed on replacement of MgO by CaO which may be attributed due to an increase in basicity of the glass system.

Molecular dynamics simulation of La 2O 3–Na 2O–SiO 2 glasses. II. The clustering of La 3+ cations

Clustering of high-field strength rare-earth ions in silicate glasses has been experimentally observed for a wide range of concentrations. Clustering has also been observed by molecular dynamics (MD) computer simulations over a range 1–10 mol% in soda silicate glasses. Although there have been numerous experimental studies, atomic-level details of the mechanisms that lead to clustering remain unclear. Coupling experiment with MD simulations is essential to uncovering the factors that lead to clustering. In this work, MD computer simulations are used to verify that clustering found in previous MD simulations is not an artifact of the simulation method. This work also provides clues as to the mechanism of atomic-level clustering.