Calcium Aluminosilicate Glasses Research Articles

Pump-induced refractive index changes in Tb3+ doped glasses

It now well known in laser materials, that a refractive index change appears when the active ions are pumped from ground to excited state due to the polarizability difference between ground and excited states (metastable). In this paper this effect was investigated in Tb3+ doped glasses: calcium alumino phosphate (CAP), low-silica calcium aluminosilicate (LSCAS) and calcium aluminosilicate (CAS). The measurements were performed using the time resolved Z-scan technique, with an Ar+ laser at 488nm, close to the resonance of 7F6→5D4 absorption line, where 5D4 is a metastable state. We obtained for low-silica calcium aluminosilicate glass Δαp~10−24cm3 which is the highest value ever reported for a RE doped material.

Emission tunability and local environment in europium-doped OH−-free calcium aluminosilicate glasses for artificial lighting applications

The relationship between emission tunability and the local environment of europium ions in OH−-free calcium aluminosilicate glasses was investigated, focusing on the development of devices for artificial lighting. Significant conversion of Eu3+ to Eu2+ was obtained by means of melting the glasses under a vacuum atmosphere and controlling the silica content, resulting in broad, intense, and tunable luminescence ranging from blue to red. Electron spin resonance and X-ray absorption near edge structure measurements enabled correlation of the luminescence behavior of the material with the Eu2+/Eu3+ concentration ratio and changes in the surrounding ions' crystal field. The coordinates of the CIE 1931 chromaticity diagram were calculated from the spectra, and the contour maps showed that the light emitted from Eu2+ presented broad bands and enhanced color tuning, ranging from reddish-orange to blue. The results showed that these Eu doped glasses can be used for tunable white lighting by combining matrix composition and the adjustment of the pumping wavelength.

Mechanisms of optical losses in the 5D4 and 5D3 levels in Tb3+ doped low silica calcium aluminosilicate glasses

Trivalent Tb-doped materials exhibit strong emission in the green and weak emission in the UV-blue levels. Usually, this behavior is attributed to the cross relaxation (CR) process. In this paper, the luminescence properties of Tb3+-doped low silica calcium aluminosilicate glasses are analyzed for UV (λexc = 325 nm) and visible (488 nm) excitations. Under 325 nm excitation, the intensity of green luminescence increases proportionally to Tb3+ concentration. However, the blue luminescence intensity is strongly reduced with the increase of concentration from 0.5–15.0 wt. %. In the case of 488 nm excitation, a saturation behavior of the green emission is observed at intensities two orders of magnitude smaller than expected for bleaching of the ground state population. Using a rate equation model, we showed that this behavior can be explained by an excited state absorption cross section two orders of magnitude larger than the ground state absorption. The blue emission is much weaker than expected from our rate equations (325 nm and 488 nm excitation). We concluded that only the CR process cannot explain the overall feature of measured luminescence quenching in the wide range of Tb3+ concentrations. Cooperative upconversion from a pair of excited ions (5D3:5D3 or 5D3:5D4) and other mechanisms involving upper lying states (4f5d, charge transfer, host matrix, defects, etc.) may play a significant role.

Thermal properties, density and structure of percalcic and peraluminus CaO–Al2O3–SiO2 glasses

Calcium silicate and aluminosilicate glasses with various SiO2 contents (10–76mol%) were prepared in the wide range of [Al2O3]/[CaO] molar ratio from 0.10 to 4.00 by conventional melt-quenching method and an aerodynamic levitation device for a part of peraluminus glasses. Variations of glass transition temperature, the coefficient of linear expansion, and ionic packing factor derived from density measurements with [Al2O3]/[CaO] molar ratio were studied. The glass structures of SiO4 three dimensional network, mixed anions of (Si, Al)O4 tetrahedra, isolated AlO4 and Al–O–Al linkages were evaluated by FT-IR measurements. Compositional dependences of the properties are qualitatively related to the glass structure examined by IR spectroscopy and the proportions of AlOx (x=4, 5, 6) species evaluated in a previous study by using 27Al MQ NMR spectroscopy.

Synthesis and luminescent properties of Eu3+/Eu2+ co-doped calcium aluminosilicate glass–ceramics

Eu3+ and Eu2+ co-doped calcium aluminosilicate glass–ceramics have been prepared by devitrification of calcium aluminosilicate glass using heat-treatment. Control of crystallization in the glass–ceramics was studied by X-ray diffraction (XRD) and Raman spectroscopy. The results showed that crystalline phases in glass–ceramic belong to the family of melilite Ca2Mg0.25Al1.5Si1.25O7 as the major phase and anorthite CaAl2Si2O8 as the minor phase. Luminescent properties were investigated by emission; lifetime and the color points were calculated. Emission spectra showed that Eu2+ entered into the crystalline phase in a two steps mechanism: first as Eu3+ which is then reduced to Eu2+. This incorporation in the crystal enhanced Eu2+ emission with increasing time of heat-treatment and therefore crystallization.

Surface Chemistry of Calcium Aluminosilicate Glasses

The surface chemistry of synthetic calcium aluminosilicate glasses exposed to aqueous solutions of varying pH was described using zeta potential measurements and batch surface titrations. Element release and proton consumption were measured to characterize the reactions at the surface as a function of pH. It was found that proton–metal exchange or leaching was the dominant proton consumption process at low pH. The exchange reaction was observed to maintain charge balance, indicating that over the limited duration of the experiments no repolymerization of the silica‐rich leached layer occurred. At high pH, dissolution and hydrolysis of aqueous ions controlled the proton mass balance, no evidence for the formation of leached layers was found. Silica‐rich glasses were found to be more resistant to corrosion by either proton–metal exchange or dissolution than CaO‐rich glasses. Glass basicity was found to be reflected in the establishment of a higher pH when immersing the glass in neutral aqueous solutions and in a reduced stability of the glass surface toward aqueous solutions. High pH, high surface charge and reduced glass network polymerization act together in enhancing the reaction of CaO‐rich glasses with aqueous solutions.

Nd3+ doped CAS glasses: A thermo-optical and spectroscopic investigation

Previous works have showed that calcium aluminosilicate (CAS) glasses, when prepared under vacuum conditions, are good candidates for solid state laser medium hosts and optical devices due to their appropriated thermal, optical and mechanical properties. These promising results led us to investigate the thermo-optical properties and emission spectra as a function of temperature in Nd3+ doped CAS glasses. Temperature changes in optical systems can cause structural modifications to the host, as well as other effects, such as emission quenching, or self-focalization. In this work, two series of CAS glasses, doped up to 5wt.% Nd2O3, were prepared and characterized. Measurements of thermal coefficient of optical path length (dS/dT) and emission were performed on both series of Nd3+ doped CAS. In addition, measurements of optical absorption coefficient and emission lifetime were carried out. The results are discussed in terms of temperature dependence of these properties and Nd2O3 content. Comparisons with other glasses, such as LSCAS (low-silica calcium aluminosilicate) are also presented.

Structural, vibrational, and elastic properties of a calcium aluminosilicate glass from molecular dynamics simulations: The role of the potential

We study a calcium aluminosilicate glass of composition (SiO2)0.60(Al2O3)0.10(CaO)0.30 by means of molecular dynamics. To this end, we conduct parallel simulations, following a consistent methodology, but using three different potentials. Structural and elastic properties are analyzed and compared to available experimental data. This allows assessing the respective abilities of the potentials to produce a realistic glass. We report that, although all these potentials offer a reasonable glass structure, featuring tricluster oxygen atoms, their respective vibrational and elastic predictions differ. This allows us to draw some general conclusions about the crucial role, or otherwise, of the interaction potential in silicate systems.

Hydroxyl speciation in felsic magmas

The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27Al–1H cross polarization and quantitative 1H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1H NMR partial spectrum was derived from the 27Al–1H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si–O–Si, Si–O–Al and Al–O–Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al–O–Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84–89% and 68–78%, respectively), but with a significant fraction of Al-OH (11–16% and 22–32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH+SiOH) ratio is likely smaller than the Al/(Al+Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al+Si) ratio at higher temperatures.

Bioactivity potential of calcium alumino-silicate glasses and glass–ceramics containing nitrogen and fluorine

Calcium alumino-silicate glasses of general composition (in eq.%) 28Ca:57Si:15Al:[100 − (x + y)]O:xN:yF (x = 0 or 20 and y = 0, 3 or 5) and their glass–ceramic counterparts were immersed in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days to assess their potential bioactivity. The glasses showed no Ca release or surface calcium phosphate deposition due to their high network connectivities (>2.55). The glass–ceramics all showed potential bioactivity, as the SBF became enriched in Ca and calcium phosphate deposits formed on their surfaces. This was a result of Ca release from crystalline phases (predominantly wollastonite in the case of CaSiAlOF glass–ceramics and gehlenite in the case of CaSiAlONF glass–ceramics). No aluminium was leached from the glass–ceramics into the SBF, due to its pH always exceeding 7.0.

Stokes–Einstein violation and fragility in calcium aluminosilicate glass formers: a molecular dynamics study

A series of classical molecular dynamics simulations of calcium aluminosilicate (CAS) (CaO–Al2O3)1–x(SiO2)x melts with varying silica content x, along the CaO/Al2O3 concentration ratio R = 1, have been performed for the purpose of studying (i) the evolution of fragility with silica content and (ii) the temperature and composition evolution of self-diffusion coefficients, viscosity and α-relaxation times. Our results indicate a decrease in the fragility of the CAS systems along R = 1 from calcium aluminate to pure silica. It is found that upon cooling, the Stokes–Einstein relation breaks down at a temperature significantly higher than the critical temperature of the mode-coupling theory TC for all compositions and also above the melting point.

Resonant excited state absorption and relaxation mechanisms in Tb^3+-doped calcium aluminosilicate glasses: an investigation by thermal mirror spectroscopy

Resonant excited state absorption (ESA) and relaxation processes in Tb(3+)-doped aluminosilicate glasses are quantitatively evaluated. A model describing the excitation steps and upconversion emission is developed and applied to interpret the results from laser-induced surface deformation using thermal mirror spectroscopy. The fluorescence quantum efficiency of level (5)D(4) was found to be close to unity and concentration independent while, for the level (5)D(3), it decreases with Tb(3+) concentration. Emission spectroscopy measurements supported these results. ESA cross sections are found to be more than three orders of magnitude higher than the ground state absorption cross section.

Interaction between composition and temperature effects on non-bridging oxygen and high-coordinated aluminum in calcium aluminosilicate glasses

The configurational changes that occur with temperature, and how these vary with composition, affect the thermodynamic and transport properties of aluminosilicate melts but are not well understood. We present here high-resolution 27 Al and 17 O NMR data on several calcium aluminosilicate glasses along two silica isopleths crossing the metaluminous (SiO 2 -CaAl 2 O 4 ) join, prepared with varying quench rates and thus with fictive temperatures spanning approximately 100 K. In all compositions, five-coordinated aluminum increases with increasing fictive temperature. For glasses along the 60 mol% SiO 2 isopleth, NBO also increases with increasing fictive temperature; this is less obvious for the glasses along the 30 mol% SiO 2 isopleth. The data suggest the mixing of bridging oxygen contributes to the magnitude of the observed temperature effect on NBO and continue to suggest the existence of multiple mechanisms that generate NBO and V Al.

Composition Influence on the Thermo-optical Properties and Luminescence Efficiency of Europium-Doped Calcium Aluminosilicate Glasses

In this work, the influence of the composition on the thermal and thermo-optical properties and luminescence of europium-doped calcium aluminosilicate glasses is investigated. High purity reagents were used to prepare samples with nominal compositions: \(2.5\hbox {Eu}_{2}\hbox {O}_{3},\,4.1\hbox {MgO},\,(7 + x)\hbox {SiO}_{2},\,(47.4 - x/2)\hbox {CaO},\,\hbox {and} (39 - x/2)\hbox {Al}_{2}\hbox {O}_{3},\,x = (0, 22, 27, 32, 37, 42,\,\hbox {and}\,47)\,(\hbox {in mass}\%)\). The ratio CaO/ Al\(_{2}\)O\(_{3}\) was kept at 1.2. At room temperature, measurements of the specific heat, mass density, temperature coefficient of the optical path length, and refractive index were performed. Two-beam thermal lens spectroscopy in the mismatch mode was used to determine the absolute values of the thermal diffusivity at room temperature. Using the thermal lens signal, the rate of heat generated by the nonradiative process was estimated, which showed a large decrease with increasing silica content. The decrease of this parameter can be related to the increase of the luminescence efficiency, which agrees with the results of luminescence spectroscopy. These results suggest an increase in the luminescence efficiency of europium-doped calcium aluminosilicate glasses at increments of increasing silica content.

Spectroscopic studies and downconversion luminescence in OH−-free Pr3+–Yb3+ co-doped low-silica calcium aluminosilicate glasses

We report on spectroscopic studies and downconversion luminescence in OH−-free Pr3+–Yb3+ co-doped low-silica calcium aluminosilicate glasses (LSCAS). The dependencies of the visible to near-infrared emissions, photoacoustic signals, luminescence decay times and energy transfer efficiencies from Pr3+→Yb3+ on the doped Yb2O3 concentration were investigated. The results confirmed the occurrence of downconversion processes in the examined samples, followed by a back-energy transfer mechanism from the Yb3+:2F5/2 level to the Pr3+:1G4 level, from where the multiphonon relaxations through the 1G4,3F4→3H4 transitions occurred. The photoacoustic data provided evidence of the energy transfer that resulted in heat generation in the sample, confirming the observations provided by the luminescence data. The energy transfer mechanisms that are involved in the Pr3+:Yb3+ co-doped LSCAS glasses are discussed.

Solution‐Controlled Dissolution of Supplementary Cementitious Material Glasses at pH 13: The Effect of Solution Composition on Glass Dissolution Rates

Supplementary cementitious materials (SCMs) are widely used to partially replace portland clinker in blended cements. Reducing clinker contents further without compromising the development of early strength necessitates a better assessment and enhancement of the reactivity of the available SCMs. To this purpose, the reactivity of synthesized calcium aluminosilicate glasses covering a compositional range from blast‐furnace slags (BFS) over fly ashes to silica fume was analyzed by dissolution experiments. Initial glass dissolution rates were measured at 20°C and pH 13, and with varying initial concentrations of aqueous Al, Ca, and Si. At pH 13, glass dissolution rates were observed to scale linearly with the glass Ca/(Al + Si) molar ratio. Ca‐rich blast‐furnace type glass dissolution was shown to be up to one order of magnitude faster than tectosilicate fly ash and silica fume type glass dissolution, supporting different pathways to dissolution. In solutions that are strongly undersaturated with respect to hydrous glass and hydration products, glass dissolution rates are independent of changes in solution undersaturation and aqueous Si activity. In contrast, dissolution rates decrease with aqueous Ca concentration for all glasses and with aqueous Al concentration for tectosilicate‐type glasses. The insights gained are instrumental in finding ways to enhance SCM reactivity.

Near-infrared quantum cutting in OH− free Nd3+-Yb3+ co-doped low-silica calcium aluminosilicate glasses

Near-infrared (NIR) quantum cutting (QC) through downconversion (DC) in OH− free Nd3+-Yb3+ co-doped low-silica calcium aluminosilicate glasses (LSCAS) was observed. Luminescence and time-resolved measurements allowed the investigation of the origin of the Yb3+ DC emission. Our results showed that only one NIR photon is emitted by the Yb3+ ion through one-step energy transfer after excitation with a VIS photon absorbed by the Nd3+ ion. However, after excitation with an UV photon absorbed by the Nd3+ ion, two NIR photons are emitted by the Yb3+ ion through two-step energy transfer. The Yb3+ DC normalized intensities after excitation at 325 nm showed an increase of a factor of two compared to that of 514 nm excitation. In addition, the energy transfer probabilities from Nd3+ to Yb3+ were estimated by analyzing the Yb3+ DC kinetics. The overall results showed an efficient QC through DC process in Nd3+-Yb3+ co-doped LSCAS glasses, and the energy transfer mechanisms are discussed.

Eu2+-doped OH− free calcium aluminosilicate glass: A phosphor for smart lighting

In this paper, a broad emission band from Eu2+-doped OH− free calcium aluminosilicate glass is reported. By changing the excitation wavelengths, the results showed it is possible to tune the emission from green to orange, what combined with the scattered light from the same blue LED used for excitation, provided a color rendering index of 71 and a correlated color temperature of 6550K. Our preliminary tests indicate this material as a promising phosphor towards the development of smart lighting devices.

Spectroscopic investigation and heat generation of Yb^3+/Ho^3+ codoped aluminosilicate glasses looking for the emission at 2 μm

Energy transfer (ET) and heat generation processes in Yb3+/Ho3+-codoped low-silica calcium aluminosilicate glasses were investigated using thermal lens (TL) and photoluminescence measurements looking for the emission around 2.0 μm. Stepwise ET processes from Yb3+ to Ho3+, upon excitation at 0.976 μm, produced highly efficient emission in the mid-infrared range at around 2.0 μm, with high fluorescence quantum efficiency (η1∼0.85 and independent of Ho3+ concentration) and relatively very low thermal loading (<0.4) for concentration up to 1.5% of Ho2O3. An equation was deduced for the description of the TL results that provided the absolute value of η1 and the number of emitted photons at 2.0 μm per absorbed pump photon by the Yb3+ ions, the latter reaching 60% for the highest Ho3+ concentration. These results suggest that the studied codoped system would be a promising candidate for the construction of photonic devices, especially for medical applications.

Thermal conductivity of low-temperature sintered calcium aluminosilicate glass–silicon nitride whisker composites

A new type of low temperature co-fired ceramic (LTCC) composite, comprising β-Si3N4 whiskers and calcium aluminosilicate (CAS) glass, is introduced in this paper. We show that the CAS–Si3N4 composite can be densified at 775–850 °C in air. The effect of β-Si3N4 whiskers incorporation on the thermal conductivity of this relatively low-temperature sintered CAS–Si3N4 composite is investigated. The thermal conductivity of the CAS glass is increased from 1.6 to 7.9 W/mK after adding 35 vol% of β-Si3N4 whiskers. Microstructure characterization and percolation model analysis indicate that the likely cause of increased thermal conductivity of the ceramic composites is the formation of thermal percolation networks. The crystallization of the CAS glass also contributes to the enhancement of thermal conductivity. The sample with the highest thermal conductivity shows a low relative dielectric constant of 7.1 and a dielectric loss of 0.006 at 1 MHz. Such a ceramic composite with excellent thermal and dielectric properties is a promising LTCC substrate material.