Lithium Aluminoborate Glasses Research Articles

Structural, vibrational, and luminescent properties of pure and Ce-doped magnesium lithium aluminoborate glass

The objective of this work was to study the properties of new vitreous samples of pure BAlMgLi and Ce-doped BAlMgLi produced by the melt-quenching method. The structural and vibrational characteristics of the samples were analyzed using x-ray diffraction (XRD), vibrational Raman spectroscopy, and vibrational Fourier transform infrared spectroscopy (FTIR). Optically stimulated luminescence (OSL) and thermoluminescence (TL) techniques were also used to identify whether the samples showed a response to ionizing radiation. XRD analyses confirmed the predominance of the amorphous phase of the samples. The Raman spectra revealed that the atomic bonds present in the material matrix are of the pyroborate and metaborate type, enabling stretching vibrations in isolated BO4 and/or Al–O or Al–O–B units. The band at approximately 810 cm−1 is characteristic of the formation of the boroxol ring, indicating that the presence of other elements in the matrix does not affect its glassy characteristics. The FTIR analyses reinforce the results found by Raman spectroscopy, because bands characteristic of low hygroscopic glasses were observed, due to the conversion of BO3 units into BO4 in triborate, tetraborate, and pentaborate groups. This conversion is due to dopant entrainment, which contributes to the high optical transparency of the samples. Their OSL and TL signals were reproducible with intensities dependent on the dopant concentration and radiation dose, with the most intense emissions resulting from 0.5% Ce concentrations.

Mechanical and Electrochemical Properties of Lithium Aluminoborate Glasses

The elastic moduli and the indentation behavior of glasses from the xLi2O-5Al2O3-(95−x)B2O3 system, with x = 35, 40, and 50 were characterized. Glasses become softer and less resistant to indentation cracking as the lithium content is increased, as a result of increasing the numbers of 3-fold coordinated boron and non-bridging oxygen atoms in this composition range. In parallel, the ionic conductivity at 25 °C is increased from 3.7 10–10 to 5.5 10–8 S∙cm–1, and the activation energy, as measured in the 10 to 90 °C ranges is between 55 (50 % Li2O) and 65 (35 % Li2O) kJ∙mol–1, which shows that the ionic diffusion of lithium is easier in Li-rich compositions. Measurements of the conductivity under a compressive load aligned with the electric field revealed a mechanical-electrical coupling. The change of the activation energy with the stress is associated with an activation volume, and thus a stress sensitivity, that is increased with the lithium content.

Short- and medium-range structure synergistically control fracture toughness of densified aluminoborate glasses

Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.

Comparison of Dy3+-doped barium borate and lithium aluminoborate glass

The optical properties of Dy3+ in barium borate (BaB) glass are compared to those of Dy3+ in lithium aluminoborate (LiAlB) glass. Sample series with varying modifier-to-former ratio and different Dy3+ concentration are analyzed for their optical absorption, external quantum efficiency, luminescence yield, and chromaticity. The photoluminescence (PL) spectra are dominated by two emission bands in the visible spectral range, namely at 483 nm and 575 nm. The BaB as well as the LiAlB glass series show a luminescence quenching upon increasing the Dy3+ concentration, though the optical absorption increases linearly. For both, a change in the modifier-to-former ratio from 1 : 2 to 1 : 4 leads to an increase in luminescence yield with the maximum at a Dy3+ content of (0.2–0.3) at.%. Compared to LiAlB glass, the absorption coefficient as well as the PL quantum efficiency of Dy3+ are slightly lower in BaB glass. The colour impression of the BaB and the LiAlB glass series are very similar; it changes with the modifier-to-former ratio as well as the Dy3+ concentration. The analysis of the PL lifetime measurements on the basis of the Förster model yield an intrinsic Dy3+ lifetime of slightly above 900 μs. For a Dy3+ content of 0.5 at.%. and higher, the energy transfer between neighbouring Dy3+ ions is noticably enhanced.

Properties of lithium aluminoborate glasses

The density, refractive index, thermal expansion coefficient, glass transformation temperature and d.c. conductivity have been determined for a number of lithium aluminoborate glasses. The glasses studied lie on lines of constant Al2O3 to Li2O concentration with values of 0 (binary lithium borate glasses), 1/2 and 1/1. The thermal expansion coefficient passes through a minimum for all three series of glasses, while the glass transformation temperature for each series passes through a maximum. This behaviour is characteristic of the borate anomaly for all three series of glasses. Replacement of B2O3 by Al2O3 in these glasses has only a slight effect on the density and refractive index. The d.c. electrical conductivity of these glasses is controlled by the Li2O concentration, with little change due to replacement of B2O3 by Al2O3.

Dy3+-doped lithium aluminoborate glass for luminescent light guides with high luminance

Lithium aluminoborate glass optically activated with the lanthanide ion dysprosium is investigated for its potential as luminescent light guide. For this, ray-tracing simulations are performed on the basis of transmission, photoluminescence, and quantum efficiency measurements. The luminous flux at the end of the light guide depends significantly on its length as well as on the roughness of the output face. The best results are obtained for a light guide length of 70–80 mm with the side faces of the light guide coated with a 100 % reflecting mirror and a rough output face with Lambertian scattering characteristic. An additional coating of the input face with a half-transmitting mirror is investigated. The mirror is transmissive for the excitation wavelength of 388 nm but reflective for the emission bands in the visible spectral range. For this light guide, a luminance of approximately 20 cd/mm 2 is achieved for an excitation power density of 1 W/mm 2 . The geometry of the light guide (cuboid/cylinder) has only a slight effect on the maximum luminance value. • Analytical estimate of luminescence output of dysprosium-doped light guides. • Ray-tracing simulations for different lengths, surface properties, and geometries. • Maximum luminance of approximately 20 cd/mm 2 for 388-nm excitation.

Structural densification of lithium phosphoaluminoborate glasses

AbstractLithium aluminoborate glasses have recently been found to undergo dramatic changes in their short‐range structures upon compression at moderate pressure (~1 GPa), most notably manifested in an increase in network forming cation coordination number (CN). This has important consequences for their mechanical behavior, and to further understand the structural densification mechanisms of this glass family, we here study the effect of P2O5 incorporation in a lithium aluminoborate glass (with fixed Li/Al/B ratio) on the pressure‐induced changes in structure, density, and hardness. We find that P2O5 addition results in a more open and soft network, with P‐O‐Al and P‐O‐B bonding, a slightly smaller fraction of tetrahedral‐to‐trigonal boron, and an unchanged aluminum speciation. Upon compression, the cation‐oxygen CNs of both boron and aluminum increase systemically, whereas the number of bridging oxygens around phosphorous (Qn) decreases. The glasses with higher P2O5 content feature a larger decrease in Qn (P) upon compression, which leads to more non‐bridging oxygen that in turn fuel the larger increase in CN of B and Al for higher P2O5 content. We find that the CN changes of Al and B can account for a large fraction (around 50% at 2 GPa) of the total volume densification and that the extent of structural changes (so‐called atomic self‐adaptivity) scales well with the extent of volume densification and pressure‐induced increase in hardness.

Colour shift in Dy3+-doped lithium aluminoborate glass

The optical properties of Dy3+-doped lithium aluminoborate glass are investigated. Sample series of varying modifier-to-former ratio and different Dy3+ concentration are analysed for their optical absorption, quantum efficiency, photoluminescence yield, and chromaticity. The samples show a luminescence quenching upon increasing the Dy3+ concentration, though the optical absorption increases linearly. Changing the modifier-to-former ratio in favour of the network former leads to an increase in luminescence yield. For all samples, the photoluminescence spectra are dominated by two emission bands in the visible spectral range, namely at 483nm and 575nm. The relative contribution of these bands to the total luminescence changes with the modifier-to-former ratio as well as the Dy3+ concentration. The colour impression of the samples changes accordingly.

Far-field studies on Eu[formula omitted]-doped lithium aluminoborate glass for LED lighting

The luminous intensity distribution from luminescent glass disks is investigated. For this, the disks are placed on top of an ultraviolet and a blue LED and the emission from the optically-activated glass is recorded in the far field. The luminous intensity distribution of the LED light and the Eu3+ luminescence is considered separately by filtering the LED excitation, the same applies to the measured total luminous flux. Angle-dependent spectra are also measured and the changes in color coordinates are examined versus the viewing angle. The experimental results of the luminous intensity distribution curves are compared with ray-tracing simulations.

Tb3+, Eu3+, and Dy3+ doped lithium borate and lithium aluminoborate glass: Glass properties and photoluminescence quantum efficiency

The glass properties as well as the photoluminescence quantum efficiency of Li2O-B2O3 and Li2O-Al2O3-B2O3 glasses are investigated; both glass systems are optically-activated by the addition of the lanthanide ions Tb3+, Eu3+, and Dy3+. Glass transition, glass crystallization, and glass melting temperatures as well as glass forming temperature ranges are determined upon varying the modifier-to-former (Li2O-to-B2O3) ratio in the range between 1:6 to 1:2. For lithium borate glass, the risk of spontaneous crystallization decreases upon decreasing the lithium concentration. The photoluminescence quantum efficiency increases slightly upon decreasing the lithium concentration with the value of a Al2O3-containing sample always lower than that of the Al2O3-free correspondent.

Competitive effects of modifier charge and size on mechanical and chemical resistance of aluminoborate glasses

Lithium aluminoborate glasses exhibit high resistance to cracking under contact loading, but low hardness and poor chemical durability in aqueous media. On the other hand, alkaline earth aluminoborate glasses feature improved chemical resistance and hardness, but lower resistance to cracking. In this work, we investigate the possibility to simultaneously improve the mechanical and chemical resistance of aluminoborate glasses by mixing alkali and alkaline earth modifiers. We study the mixed Li/Ba and Li/Mg aluminoborate glasses, since Li+ and Ba2+ have different charge and size but similar modifier field strength (charge to size ratio), while Mg2+ has the highest field strength among these modifiers due to its small size. The two glass series will thus give insights into the competitive effects of modifier charge and size on glass structure, mechanical properties, and dissolution rates in acidic, neutral, and basic solutions. The substitution of barium for lithium at fixed [Al2O3]/[B2O3] ratio does not affect the network structure and properties, such as hardness and dissolution rate. However, the substitution of magnesium for lithium leads to an increase in hardness and chemical durability for all pH solutions (2, 7, and 14), likely as a result of the increase in the fractions of five- and six-fold coordinated aluminum species and atomic packing density. The glass with 5 mol% Li2O and 20 mol% MgO exhibits the best combination of high hardness and low dissolution rate, while maintaining a good crack-resistance comparable to that of the Li-aluminoborate glass. In both mixed glass series, the lowest dissolution rates are measured in neutral solutions, while those in acidic and especially basic media are higher. The structural origins of the trends in chemical and mechanical properties are discussed based on 11B and 27Al nuclear magnetic resonance (NMR) spectroscopy measurements.

Eu2O3 doped bright orange-red luminescent lithium alumino-borate glasses for solid state lighting

In present study, Eu2O3 doped Li2O:Al2O3:B2O3 glasses (LABE) were synthesized by melt quenching technique. Physical, thermal, structural and spectroscopic properties of prepared glasses have been investigated by various techniques. X-ray Diffraction (XRD) spectroscopy confirms the amorphous nature of glass samples. FTIR spectra show various structural groups present in the present glass system. Luminescence spectra exhibit emission bands in the visible region from 570 to 725 nm. The emission peaks are located at 577.5, 589.5, 613.5, 652, 701 nm attributed to the 5D0→7F0, 1, 2, 3 and 4 transitions. The CIE chromaticity diagram discloses glass LABE-4 having colour coordinates x = 0.63, y = 0.34 shows highest emission intensity among all glass samples. The glass LABE-4 lying in the red region of CIE 1931 chromaticity diagram and has been found well suited for solid-state lighting application.

Discovery of Ultra-Crack-Resistant Oxide Glasses with Adaptive Networks

Despite their transformative role in our society, oxide glasses remain brittle. Although extrinsic postprocessing techniques can partially mitigate this drawback, they come with undesirable side effects. Alternatively, topological engineering offers an attractive option to enhance the intrinsic strength and damage resistance of glass. On the basis of this approach, we report here the discovery of a novel melt-quenched lithium aluminoborate glass featuring the highest crack resistance ever reported for a bulk oxide glass. Relying on combined mechanical and structural characterizations, we demonstrate that this unusual damage resistance originates from a significant self-adaptivity of the local atomic topology under stress, which, based on a selection of various oxide glasses, is shown to control crack resistance. This renders the lithium aluminoborate glass a promising candidate for engineering applications, such as ultrathin, yet ultrastrong, protective screens.

Tm/Tb/Eu triple-doped lithium aluminoborate glass for white light generation

The aim was to design a multi-chromatic phosphor based on the colour mixing principle, whereby white light can be produced from an appropriate mixture of blue, green, and red emissions by a single phosphor. In this perspective, Tm2O3, Tb4O7, and Eu2O3 were simultaneously doped in single host glass matrix. A series of Tm2O3 single- as well as Tm/Tb/Eu triple-doped glasses were synthesised. The photoluminescence behaviour and luminescence quenching were investigated for Tm2O3 single-doped glasses. Keeping Tm2O3 constant at the saturation concentration in the Tm/Tb/Eu triple-doped glasses and varying the doping ratio of the two other lanthanides (Tb4O7 and Eu2O3) in the host glass allow to some extent the control of the spectral composition and consequently the generation of tunable colour impressions. The latter can also be adjusted by keeping the concentration ratio of the three lanthanides constant and varying the excitation wavelength. Upon 358-nm excitation of the Tm/Tb/Eu triple-doped glasses, white light emission is achieved and the corresponding correlated colour temperatures are also determined. The different energy transfers occurring in between the three lanthanides are investigated and possible energy transfer routes are proposed.

Physical, thermal, structural and optical properties of Dy3+ doped lithium alumino-borate glasses for bright W-LED

Rare earth (RE) doped glasses have potential applications due to their emission efficiencies of 4f–4f and 4f–5d electronic transitions. Among all the rare earths, Dy3+ doped glasses have drawn much interest among the researchers for their intense emission in the visible region from 470 to 500nm and around 570 to 600nm. The physical, thermal, structural and optical properties of Dy3+ doped lithium alumino-borate glasses (LABD glasses) have been studied for white LED (W-LED) application. The glasses were synthesized by conventional melt quench technique. X-ray diffraction spectra revealed the amorphous nature of the glass sample. An FTIR spectrum was carried out to study the glass structure and various functional groups present in the LABD glasses. Optical absorption spectra were recorded by UV–vis-NIR spectrometer. Allowed direct and indirect band gaps were obtained by Tauc's plot. Thermal parameters like glass thermal stability (∆T), Hruby's parameter (Kgl), etc. were calculated by DTA graph. Photoluminescence excitation and emission spectra's were measured at room temperature. The emission spectra shows two intense emission bands at around 482nm (blue) and 574nm (yellow) corresponds to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions respectively along with one feeble band at 662nm (red) corresponds to 4F9/2→6H11/2 transition. The CIE chromaticity co-ordinates were calculated for all glass samples. CIE chromaticity diagram shows glass LABD-4 containing 0.5mol% Dy2O3 with colour co-ordinates X = 0.34 and Y = 0.38 have highest emission intensity. These glasses having emission in the white region and thus can be used for bright white LED.

Excitation induced spectroscopic study and quenching effect in cerium samarium codoped lithium aluminoborate glasses

Lithium aluminium borate host has been codoped with cerium and samarium to prepare glass by conventional melt quench technique. Their structural and spectroscopic investigation has been carried out using XRD, FTIR and density measurements. The UV‐Vis absorption spectra and fluorescence spectra (λexc.=380nm and 400nm) have been studied for spectroscopic analysis. The amorphous nature of the prepared samples is shown by XRD. The density is increasing with addition of cerium at the expense of aluminium, keeping other components constant. FTIR study also shows the presence of compact and stable tetrahedral BO4 units thus supporting the density results. The UV‐ Vis absorption spectra show a shift of optical absorption edge towards longer wavelength along with an increase in intensity of peaks with rising samarium concentration. The fluorescence spectra show a blue shift and subsequent suppression of cerium peaks with addition of samarium.

Cerium and samarium codoped lithium aluminoborate glasses for white light emitting devices

Cerium and samarium codoped lithium aluminium borate glasses are prepared by using conventional melt quench technique and their structural and spectroscopic analysis has been done. The structural studies have been done using XRD, FTIR and density measurements. The spectroscopic analysis has been done using UV–Vis absorption spectra and fluorescence emission spectra by exciting the glass samples at 380nm and 400nm. XRD confirms the amorphous nature of the prepared samples. The density shows an increasing trend with addition of cerium at the expense of aluminium, other components being constant. This is also confirmed by FTIR study which shows the conversion of trigonal BO3 units into more stable tetrahedral BO4 units. The UV–Vis absorption spectra shows an increase in intensity and a significant shift of the optical absorption edge from UV to partially visible region when cerium is added in the pure samarium containing lithium aluminium borate glass. The fluorescence spectra indicate an energy transfer from Ce3+ to Sm3+ ions. Moreover, some of the glass compositions may be found suitable for white light emitting devices as there is a simultaneous presence of red, green and blue emission.

Sm3+ doped lithium aluminoborate glasses for orange coloured visible laser host material

Samarium doped lithium aluminium borate glasses have been prepared by conventional melt quench technique and their detailed spectroscopic analysis has been done. The structural analysis has been done by using FTIR studies and density is measured by Archimedes method. The UV–vis–NIR absorption spectra show an increase in intensity of different transitions from the ground level 6H5/2 to various 2S+1LJ levels with an increase in samarium concentration at the expense of aluminium. The fluorescence spectra show several transitions from 4G5/2 to various 6HJ levels along with 4F3/2 to 6HJ and 4G7/2 to 6H5/2.

Hollow glass microspheres for use in radiation shielding

The production of hollow glass microspheres from Li 2O–Al 2O 3–B 2O 3 glasses was investigated. The production of hollow, rather than solid, spheres is enabled by the use of blowing agents in the glass, such as sulfate compounds. Irregular glass frit (25–100 μm in diameter) was fed into a propane/oxygen torch and spherodized. Solid spheres were easily obtained for all particle sizes and glass compositions studied, but the yield of spheres with single hollow cavities was very low. Raman scattering spectroscopy was performed on glass frit to determine glass structure and the presence of sulfur-containing groups. Glasses were batched to contain SO 3, but Raman spectra show the presence of bands due to SO 4 2 - . The Raman spectra presented do not show a clear relationship between glass composition (structure) and the yield of solid or hollow spheres. The solubility of sulfate in lithium aluminoborate glasses is around 1 wt%, based on the appearance of white Li 2SO 4 inclusions in glasses made to contain 1 wt% SO 3 or greater. Sulfate solubility in glass samples was also seen to decrease with increasing Al 2O 3 content.

The influence of aluminum oxide on the thermal expansion, glass transition temperature, and viscosity of lithium and sodium aluminoborate glasses

The glass transition temperatures and thermal expansion coefficients below and above the glass transition range are determined for lithium and sodium aluminoborate glasses over a wide range of concentrations. The temperature dependences of the viscosity for sodium aluminoborate and certain lithium aluminoborate glasses are studied in the viscosity range 1010.5–105 P. The data obtained are compared with the results of earlier investigations into the properties of barium aluminoborate glasses. The composition dependences of the properties studied are interpreted in the context of possible changes in the boron and aluminum coordination.