Predictable tendency of Bi NIR emission in Bi‐doped magnesium aluminosilicate laser glasses

Because of superbroad luminescence in the range of near infrared (NIR), Bi‐doped glasses and fibers have received more attentions recently for the applications in super broadband optical fiber amplifiers or new wavelength lasers. As the luminescence comes from the transitions between naked 6p orbitals of bismuth, it is very susceptible to slight changes of local field around Bi. Therefore, it is always very challenging to predict NIR emission of bismuth in advance. Here, we found bismuth NIR emission shows predictable tendency in ternary glass system of MgO–Al₂O₃–SiO₂. The emission peak shifts red along the content of magnesium upon the excitation of 484 nm, which follows a single exponential growth equation. In the meantime, the full width at half maximum (FWHM) is broadened while the lifetime keeps decreasing. Glass structure analysis on basis of FTIR, ²⁷Al NMR, ²⁹Si NMR spectra reveals that these changes correlate to integrity of glass network, the increased disorder of local field around bismuth and the enhanced interaction between bismuth and host, which are perhaps due to the linear increase of nonbridging oxygen, and the enhanced Si–O asymmetric stretching vibrations along with magnesium, respectively. Electron probe microanalysis shows good homogeneity of Si, Al, Mg, Bi, and O distribution within the samples, and yoyo experiments of heating and cooling between 30°C and 300°C reveal the good resistance of such doped glasses to thermal degradation. This makes the glasses promising in applications of fiber devices even under extreme condition such as at higher temperature. The finding in this work should be helpful for the design of Bi‐doped laser glasses in future.     

掺Bi的MgO-CaO-Al2O3-SiO2玻璃的吸收和近红外发光特性

研究了4种不同Bi_2O_3掺杂量(0.5%,1%,2%和3%,摩尔分数)的23MgO-11CaO-15Al_2O_3-51SiO_2(摩尔比)玻璃的发光特性。测量了吸收光谱、荧光光谱和荧光寿命。通过电子顺磁共振图谱观察了玻璃受γ辐射前后结构的变化,探讨了玻璃颜色变化和近红外发光的机理。结果表明:在500nm激发下,随着Bi_2O_3掺杂量从1%到3%的逐渐增加,发光波长发生红移,荧光半高宽从312nm增加到352 nm;最优的Bi_2O_3掺杂量为1%,玻璃的受激发射截面和荧光寿命的乘积为3.10×10~(-24)cm~2·s;γ辐射后发光强度的增加和玻璃颜色加深的现象说明Bi掺杂玻璃的近红外发光中心可能是低价态的Bi离子或者Bi团簇。     

New strategy to enhance the broadband near‐infrared emission of bismuth‐doped laser glasses

Bismuth‐doped glasses and fibers with broadband near‐infrared (NIR) emission have garnered much attention on account of their potential applications in new fiber lasers and broadband amplifiers. Yet the realization of high gain from Bi‐doped fibers and highly efficient NIR emission from Bi‐doped glasses are still a stubborn puzzle. The enhancement of Bi NIR emission is normally based on modifying the glass composition and topology, which will change the structure of the glass over a wide range and alter the thermal or mechanical properties of the glass simultaneously, making it more complicated for the designing and fabricating of Bi fibers with good performance. Here, we find that a trace addition of Si₃N₄ can efficiently enhance the Bi NIR emission without changing the glass structure significantly, right followed by spectral and structural analysis. ²⁷Al NMR measurement reveals that the short‐ to medium‐range order of this glass is unchanged. The EPMA measurement confirms the homogeneity of fabricated glass. The great enhancement and red‐shift under blue light excitation may originate from the conversion of Bi active centers to low valence. Our results indicate that the trace addition of nitride could be a facile and maneuverable way to control the valence of active ions in glasses, which may contribute to improving the performance of photonic glasses.     

Atomic and micro-structure features of nanoporous aluminosilicate glasses from reactive molecular dynamics simulations

Long-term chemical durability of borosilicate glasses that makes them a widely accepted form of nuclear waste disposal is achieved through the formation of a porous aluminosilicate gel layer that provides passivity and limits the transport of water to the reaction front. Detailed understanding of the porous silicate gel layer is thus critical in elucidating the corrosion mechanism of these glasses and to design of new glass composition for waste immobilization and other applications. In this paper, we use the diffuse charge reactive potential to generate porous aluminosilicate glass structures with compositions equivalent to the gel layers formed at the glass-water interface with an aim to understand the processing condition on the microstructure and atomic structure of these systems. We demonstrate the use of the charge scaling techniques is an effective approach to generate these porous structures with controllable pore mophologies. After initial validation of the potentials and calcium aluminosilicate glass structures using neutron diffraction, we created gel structures with compositions similar to well-known model nuclear waste borosilicate glasses. The porosities and the pore size distribution bear a strong correlation to the processing temperature, as well as to the local atomic structure. Thus, by controlling the processing parameters, the generated porous structures can be customized to closely resemble gel structures due to borosilicate glass corrosion. These results provide insights of the micro- and atomic structure features of the porous aluminosilicate glasses and on the optimal procedure to generate porous structures that can be comparable to experimentally observed gel layer structures thus to elaborate on the correlations between the structure and phenomena in glass-water interactions.     

Luminescence and laser action of coumarin dyes doped in silicate and aluminosilicate glasses prepared by the sol-gel technique

Coumarin dyes are encapsulated in silicate and aluminosilicate polymeric glasses synthesized by the sol-gel technique. The coumarin dyes retain their luminescent properties in all of the aged gels and in many of the dried gels (xerogels). The luminescence spectra of the new optical materials are reported. The luminescence of coumarin 4 provides a probe at the molecular level of the changes which occur during the gelation and drying. The spectral changes are studied and discussed in detail. Gels and xerogels doped with coumarin 460, 480, and 540A exhibit optical gain and laser action. The laser properties of these new solid-state dye laser materials are reported and discussed.     

Controllable ultra-broadband visible and near-infrared photoemissions in Bi-doped germanium-borate glasses

The design of functional materials with tunable broadband luminescence performance is still of great interest in the fields of lighting, solar cells, tunable lasers, and optical amplifiers. Here, via a melt-quenching method, a series of bismuth (Bi)-doped germanium-borate glasses with composition of 40GeO₂–25B₂O₃–25Gd₂O₃–10La₂O₃–xBi₂O₃ have been prepared, in which multiple Bi active centers can be stabilized simultaneously. Dual-modulating modes of visible (380-750 nm) and near-infrared (NIR) (1000-1600 nm) broadband photoemissions were effectively controlled under flexible excitation scheme. Photoluminescence (PL) spectra at low temperature 10-298 K were appropriately employed to interpret such an unusual wide visible emission band. To further illustrate the origin of NIR component, transmission electron microscopy (TEM) measurement was carried out. It is demonstrated experimentally that the visible emission mainly originates from the collective contribution of the ³P₁/³P₀¹S₀ transitions of Bi³⁺, while the broadband NIR luminescence should be related to the formation of low valent Bi⁺ and (or) Bi⁰ centers. This work may help to enhance the knowledge of the complex luminescence mechanism for the Bi species and it also enables such transparent glass materials to be a promising candidate for the multifunctional tunable light source.     

Topological hardening through oxygen triclusters in calcium aluminosilicate glasses

Molecular dynamics simulations and topological constraint theory are used to study the impact of oxygen triclusters in the calcium aluminosilicate glass system at ratios of 0.6, 1, 1.5, 2, and 4 [Al₂O₃]/[CaO]. Negligible percentages (less than ~3%) of five-coordinated Al structures are found at all ratios. Up to ~27% three-coordinated oxygens, also known as triclusters, are found at the highest ratio of [Al₂O₃]/[CaO]. A topological constraint model, which considers additional constraints provided by triclusters, is created to predict the glass transition temperature, hardness, and Young's modulus. The models are used to elucidate the role of triclusters in glass properties. Analysis of topological constraints shows that triclusters can potentially increase the glass hardness within the calcium aluminosilicate system. The results are also compared to oxynitride glasses. Triclusters show the same ability as nitrogen to increase the glass hardness but are less effective at increasing the Young's modulus.     

磷钨酸铋非均相催化合成乙酸环己酯

以乙酸酐与环己醇为原料,磷钨酸铋为催化剂,合成乙酸环己酯,考察了催化剂用量、反应时间、醇酐摩尔比对乙酸环己酯产率的影响。结果表明,磷钨酸铋催化活性良好,当乙酸酐的加入量为0.1 mol,醇酐摩尔比为1.2时,使用0.9 g催化剂,反应30 min后,乙酸环己酯收率可达到93.8%,且催化剂重复使用5次仍保持良好活性。产品经折光率和红外光谱进行了表征。     

铋、氧化铋、硫化铋在盐酸-硫脲中 溶解性的比较研究

在盐酸介质中及 55 ℃ 加热条件下,铋与硫脲形成黄色络合物,从而建立了用分光光度法比较铋、氧化铋、硫化铋在盐酸-硫脲中溶解性的新方法。研究了反应介质、试剂浓度、加热时间、加热温度、震荡速率等因素的影响。在最佳实验条件下,溶液的质量浓度为0.04～0.24 mg/mL时符合比尔定律。相关系数R=0.999 9,检出限为 1.05×10^-2 μg/mL,标准偏差SD=0.003 5,相对标准偏差 RSD=2.42％,摩尔吸收系数为1.515×10⁵ L/（mol·cm）,加标回收率为96.7%～98.8%。实验结果表明,铋、氧化铋、硫化铋的溶解性顺序大小为：铋>氧化铋>硫化铋。     

Structure and composition of surface depletion layers in poled aluminosilicate glasses

Thermal poling processes can be used to form modified surface layers on glass that, under ion-blocking electrode conditions, are depleted of virtually all network-modifying cations relative to the network-forming species. During this process, many outstanding questions remain as to the structure of these layers and how it may vary between glasses of different “parent” composition, with important implications for resultant surface properties and industrial applications of this technology. This phenomenon of depleting modifiers is particularly difficult to rationalize in aluminosilicate glass compositions, where—in the parent glass—aluminum ions are predominantly present as cation-charge-compensated [AlO4]⁻ tetrahedra prior to poling. Here, we present results of a detailed investigation into the surface depletion layers formed across a wide range of ternary sodium aluminosilicate (NAS) glasses, applying a host of surface-sensitive spectroscopy methods to directly interrogate the resulting composition and structure within the Na-depleted, anode-side surface layers. The desired depletion layers were successfully formed on all of the NAS glasses attempted, all showing (a) near-complete depletion of alkali within 300-500 nm-thick layers on the anode-side surfaces, (b) thin zones of Al depletion with the Na-depleted layer, and (c) the absence of injected H⁺ ions that could serve as an alternative charge-compensation mechanism. These data essentially confirmed a true binary Al₂O₃–SiO₂ composition inside the depletion layers. However, no significant structural dependence was found as a function of parent glass, where initial compositions ranged from peralkaline to charge-balanced. Importantly, TEM imaging showed the depletion layers to be fully amorphous and homogeneous (not phase-separated) at the nanoscale, despite final compositions in the range of 5-33 mol% Al₂O₃—a composition space notoriously prone to phase-separation if prepared by conventional melting. Within the depletion layers, ELNES and TEY-XANES evidence is shown for retention of Al in a 4-coordinated state, along with XPS data indicating elimination of non-bridging oxygen. Taken as a whole, our results indicate a highly-connected aluminosilicate network, most likely with a relatively high concentration of 3-coordinated oxygen—or O “triclusters”—as a plausible means of charge-compensating 4-coordinated Al in the absence of Na⁺ or H⁺. The combined results of this work provide convincing new evidence for unique glass structures within the depletion layers not achievable through analogous melt pathways, with important implications for surface properties.     

Synthesis,FTIR, and mechanical as well as radiation shielding characteristics in Nd2O3-doped bismuth lithium borate glasses

A melt quenching method was applied to fabricate a series of bismuth lithium borate glasses with a chemical composition of 65(B₂O₅) + 20(Bi₂O₃) + (15 ? x)(Li₂O) + x(Nd₂O₃), where x = 0, 1, 2, 3, and 4 mol%. The structural changes in the fabricate glasses were studied via the Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the manufactured glasses indicated the transformation of the structural unit BO₄. The mechanical properties of the produced glasses were evaluated via the ultrasonic measurement (longitudinal and shear velocities) and the Makishima–Mackenzie modulus calculations. Furthermore, the role of Nd₂O₃ in improving mechanical properties was studied theoretically and experimentally and results showed that ultrasonic velocities and elastic moduli decreased with increasing the Nd₂O₃ content. The Young's modulus decreased from 68.47 to 50.61 GPa as the Nd₂O₃ content increased from 0 to 4 mol%, respectively. The gamma ray shielding properties of the studied glass samples were evaluated using the Monte Carlo simulations between 0.223 and 2.506 MeV. The simulated data showed that the fabricated glass without Nd₂O₃ has the highest linear attenuation coefficient, which varied between 0.210 and 0.212 cm^?1 for photons with energies ranging from 0.2234 to 2.506 MeV.     

Concentrations of Residual Carbonate Ions in the Bi-Sr-Ca-Cu-O Glasses

It was found that the IR absorption bands appearing at 600 to 1600 cm⁻¹, which had been previously assigned to the fundamental vibrations of [BiO₃] or [BiO₆] polyhedra, are due to residual carbonate ions (CO²⁻₃) dissolved in Bi-Sr-Ca-Cu-O glasses. The concentrations of the remaining CO²⁻₃ in the Bi_2.2Sr₂Ca₁Cu₂O _x glasses that melted at 1100° and 1400°C are 170 × 10⁻⁵ mol/cm³ (3.3 mol%) and 3.2 × 10⁻⁵ mol/cm³ (0.25 mol%), respectively. The apparent activation energy for the dissociation of the carbonates was approximately 220 kJ/mol. The CO²⁻₃ content in the precursor glasses did not significantly affect the superconducting properties of the resulting glass–ceramics.     

A tetrad effect in the glass transition of lanthanide-doped sodium disilicate glasses

Scanning calorimetric determination of the glass transition temperatures (T_g) of sodium disilicate doped individually with 25 wt.% of the oxides of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu reveals the presence of the so-called “lanthanide tetrad effect” in their glass transition temperatures. This is to the best of our knowledge the first observation of a tetrad effect in the macroscopic properties of a high-temperature silicate phase.     

Spatial distribution of nucleated bubbles in molten glasses undergoing coalescence and growth

Two‐dimensional spatial distributions and growths of nucleated bubbles during the re‐melting of “float” glass samples are experimentally investigated. To follow the bubble population undergoing coalescence, the temporal behavior of the Voronoï tessellation built by the bubble positions are monitored. During coalescence, the Voronoï cell areas are fitted by a single‐parameter Gamma distribution. Numerical time simulation of population of bubbles undergoing coalescence shows an exponential increase in the parameter associated to the Gamma distribution with the fraction of coalesced bubbles in agreement with experimental observation. An initial density of nuclei is then estimated; direct observation would require an extremely high space resolution. The bubble number density is two orders of magnitude larger on the side which was in contact with tin bath than on the other side in contact with atmosphere. Moreover, bubbles grow faster on tin side. From a thermodynamic and mass transfer models, we prove that tin reduces the glass former liquid which leads to an increase in dissolved sulfur explaining the more abundant bubble population and the enhanced growth rate on tin side.     

Mechanisms of microstructural deformation governing Vickers hardness in phase-separated calcium aluminosilicate glasses

The impact of microstructure on hardness in phase-separated calcium aluminosilicate glasses is investigated. Changes in hardness are governed by microstructure deformations that occur during indentation. Phase separation leads to decreased hardness due to the incongruent yielding of the droplet and matrix phases. Moreover, the deformation of microstructures possessing dilute, spherical droplets did not have a significant impact on hardness. Microstructures characterized by concentrated, acicular droplets were found to deform through a process of droplet coalescence. This process absorbs additional energy during yielding and results in glasses that deform through droplet coalescence possessing improved hardness.     

Enhanced NIR photoemission from Bi-doped aluminoborate glasses via topological tailoring of glass structure

Bismuth (Bi)-doped laser glasses with broadband emission are of current interest in the fields of sensing, bio-imaging, and photonics. For practical applications, it must be considered how to improve the emission efficiency, in particular, for borate glasses with wide glass-forming range, low melting point, and excellent fiberizing ability. Herein, we experimentally demonstrate that addition of GeO₂ to aluminoborate glasses can effectively enhance Bi NIR emission by more than 300 times with prolonged decay time (~500 μs) and good homogeneity, which is, to our best knowledge, seldom achieved in Bi-doped borate multi-component glasses. The addition of second glass-former GeO₂, as revealed by detailed optical and structural analysis, leads to the facile regulation on local glass structure, forcing the conversion of aluminum species from AlO₅ and AlO₆ to AlO₄ and consequently pushes the conversion of Bi³⁺ to Bi⁺ and Bi⁰ and stabilizes Bi NIR centers, which finally results in highly enhanced Bi NIR emission. We believe these results could contribute to designing Bi-activated multi-component laser glass and fibers with efficient NIR photoemission.     

Crystallization kinetics and enhanced Bi NIR luminescence of transparent silicate glass‐ceramics containing Sr2YbF7 nanocrystals

Bismuth‐doped glasses and crystals have been widely investigated due to their intriguing potential applications in superbroadband fiber amplifier and lasers in new NIR spectral range. However, few reports have been devoted so far to bismuth‐doped transparent glass‐ceramics. Here, this work reports on bismuth‐doped silicate glasses and glass‐ceramics, which were prepared by melt‐quenching and consequent annealing processes, respectively. On the basis of the analyses on crystallization kinetics, nucleation and growth rate of crystalline phase can be modulated and Sr₂YbF₇ nanophase can, therefore, be precipitated uniformly inside the glass matrix in a controlled way to maintain proper transparence especially in optical telecommunication windows. Once the nanophase comes into being, enhanced bismuth NIR luminescence can be observed by more than 40 times upon excitation of 470 nm. Similar enhancement can appear upon different excitation schemes and the mechanism is discussed accordingly. Such Bi doped transparent glass‐ceramics with improved luminescence efficiency might find application in fiber lasers for future optical fiber communication.     

Tunable broadband photoluminescence from bismuth-doped calcium aluminum germanate glasses prepared in oxidizing atmosphere

Tunable photoluminescence (PL) from transparent inorganic glass matrices is of interest for applications demanding a semitransparent photoconverter that does not elastically scatter incoming light. For this purpose, bismuth (Bi)-doped optical materials exhibit unique spectral characteristics in terms of bandwidth and emission tunability. Here, we demonstrate a facile route for preparing such converters from Bi-doped calcium-aluminate and calcium-aluminogermanate glasses. These glasses offer tunable PL across the near violet and visible-to-near-infrared (NIR) spectral range, with an emission lifetime in the range of 300 μs. The addition of GeO₂ exerts a decrease in optical basicity, which in turn enables the stabilization of NIR-active low-valence Bi species for broadband NIR PL.     

Modeling the nanoindentation response of silicate glasses by peridynamic simulations

Nanoindentation is a widely used method to probe the mechanical properties of glasses. However, interpreting glasses’ response to nanoindentation can be challenging due to the complex nature of the stress field under the indenter tip and the lack of in situ characterization techniques. Here, we present a numerical model describing the nanoindentation of an archetypical soda-lime silicate window glass by means of peridynamic simulations. We show that, although it does not capture shear flow and permanent densification, peridynamics exhibits a good agreement with experimental nanoindentation data and offers a direct access to the stress field forming under the indenter tip.     

Mg and Al mixed effects on thermal properties in aluminosilicate glasses

By using the aerodynamic levitation and laser melting technique to well extend the glass-forming region into the Mg-rich and peraluminous regime, a series of magnesium aluminosilicate glasses were prepared to investigate the Mg and Al mixed effects on thermal properties, including glass transition temperature (T_g), crystallization behavior, and thermal stability. With the gradual substitution of Mg by Al, T_g exhibits two types of near-linear rises with different slopes in two compositional regions separated by r = 0.57, where r is equal to the molar ratio of [Al₂O₃]/([Al₂O₃] + [MgO]). Moreover, when it comes to other properties, that is, crystallization behavior and thermal stability, this critical point precisely appears at the same r = 0.57. Compared to the slower increase of T_g in Mg-rich region, the steeper rise of T_g in the peraluminous region is mainly ascribed to the step-by-step formation of oxygen triclusters driven by Pauling's second rule. Moreover, the occurrence of the critical point for T_g rise at r = 0.57 rather than the theoretical 0.5 can be seen as a proof of the role of Mg cations partly as a network former.