Effect of BaF2 Content on Luminescence of Rare‐Earth Ions in Borate and Germanate Glasses

Rare‐earth‐doped oxyfluoride germanate and borate glasses were synthesized and next studied using spectroscopic methods. Influence of fluoride modifier on luminescence properties of rare earths in different glass hosts was examined. The excitation and emission spectra of Pr³⁺ and Er³⁺ ions in the studied glasses were registered. The emission spectra of Pr³⁺ ions in germanate and borate glasses are quite different and depend strongly on the glass host. In samples doped with Er³⁺ ions emission bands located around 1530 nm corresponding to the main ⁴I_13/2→⁴I_15/2 laser transition were registered, independently of the glass host. Quite long‐lived near‐infrared luminescence of Er³⁺ ions was observed for germanate glasses with low BaF₂ content, while in borate glass systems influence of barium fluoride on luminescence lifetimes is not so evident. The Judd–Ofelt calculations were used in order to determine quantum efficiencies of excited states of rare‐earth ions in germanate and borate glasses.     

Understanding the Flash Sintering of Rare‐Earth‐Doped Ceria for Solid Oxide Fuel Cell

A novel electrical current applied technique known as flash sintering has been applied to rapidly (within 10 min) densify electrolytes including Ce_0.8Gd_0.2O_1.9 (GDC20), Ce_0.9Gd_0.1O_1.95 (GDC10), and Ce_0.8Sm_0.2O_1.9 (SDC20) for application in Solid Oxide Fuel Cells (SOFCs). The densification temperature for the three electrolytes was 554°C, 635°C, and 667°C, respectively, which is far below conventional sintering temperatures. All specimens after flash sintering maintained the pure fluorite structure and exhibited a well‐densified microstructure. To investigate the flash‐sintering mechanism, we have applied Joule heating effect with blackbody radiation theory, and found that this theory could reasonably interpret the flash‐sintering phenomenon by matching theoretically calculated temperature with the real temperature. More importantly, one of the materials inherent properties, the electronic conductivity, has been found correlated with the onset of flash sintering, which indicates that the electrons and holes are the primary current carriers during the start of flash‐sintering process. As a result, potential densification mechanisms have been discussed in terms of spark plasma discharge.     

A Unique Approach to Characterization of Sol‐Gel‐Derived Rare‐Earth‐Doped Oxyfluoride Glass‐Ceramics

Using the sol‐gel route Nd³⁺‐doped oxyfluoride glass‐ceramics were prepared. LiYF₄ and YF₃ crystals were deposited in the glass‐ceramics and their size, distribution, and amount ratio were varied by changing the compositions and heating temperatures. The incorporation of Nd³⁺ ions into both the fluoride crystals was confirmed by the high‐resolution elemental mapping of the glass‐ceramics. The incorporated Nd³⁺ ions showed up and down conversion photoluminescence whose properties were obviously different among the samples. The preliminary site analysis for Nd³⁺ ions was carried out using a unique approach associated with the Prony series approximation. Finally, the approach was found to be useful for the analysis of materials that are structurally complicating.     

Structure of Borate Glasses

Anomalous thermal expansion and other properties of borate glasses have previously been given a structural explanation by Abe. This explanation is here reinterpreted and revised in terms of the structon theory of Huggins. In agreement with Warren, it is postulated that, in glasses containing, in addition to boric oxide, small relative amounts of an alkali or alkaline-earth oxide, some of the boron atoms are surrounded by four oxygen atoms and all the oxygen atoms bridge between two boron atoms. At concentrations beyond that of the thermal expansion minimum, some oxygens are assumed to have only one boron neighbor. These ideas are formulated quantitatively and are used to interpret pertinent experimental data. From the concentrations where the property-composition curves show breaks, conclusions may be drawn as to the average number of oxygens surrounding each metal atom.     

Properties and Structure of Lithium Borate and Strontium Borate Glasses

Experimental results for some physical properties of Li₂O-B₂O₃ and SrO-B₂O₃ glasses with high modifier content showed anomalies in the composition dependence of many properties such as thermal expansion coefficient, transformation temperature, softening temperature, density, and refractive index at 30 to 33 mol% modifier oxide in these glasses. These anomalies are attributed to the formation of nonbridging oxygens near this composition.     

Structure and Properties of Silver Borate Glasses

Clear glasses form in the system Ag₂O-B₂O₃ up to about 35 mol% (65 wt%) Ag₂O. Infrared absorption, thermal expansion, and density data indicated an analogy to the Na₂O-B₂O₃ system. Pentaborate-triborate group pairs appear to be formed on addition of Ag₂O to B₂O₃ up to 20 mol% Ag₂O and diborate groups from 20 to 33 mol% Ag₂O. This interpretation is supported by the comparison of the infrared absorption spectra of quenched and crystallized glasses. One crystallization product, Ag₂O-4B₂O₃, was identified previously. A new compound starts to appear at 28 mol% Ag₂O. The theory that silver is generally present as a network modifier like sodium was substantiated by the comparison of the molar volume of sodium and silver borate glasses. Above 27 mol% Ag₂O some atomic silver is assumed to be present; below 15 mol%, exploratory studies indicate a two-phase structure within an immiscibility gap. A low-temperature internal friction peak in the glasses up to 28 mol% Ag₂O corresponds to the alkali peak in other glasses; a high temperature peak appearing in the 34 mol% Ag₂O glass is associated with the appearance of nonbridging oxygen in the system.     

Properties and Structure of Lanthanum Borate Glasses

Glass formation limits were determined for the lanthanum borate glasses. Stable immiscibility prevents the formation of clear glasses over the range 0 to 20 mol% La₂O₃, but excellent quality glasses could be formed between 20 and 28 mol% La₂O₃. Data are reported for the density, refractive index, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation range viscosity, helium permeability, and chemical durability of these glasses. A limited Raman and infrared spectroscopy study suggests that lanthanum plays a similar structural role in these glasses and in the related crystals.     

Self‐Activated Vanadate Compounds Toward Realization of Rare‐Earth‐Free Full‐Color Phosphors

Rare‐earth‐free phosphors based on vanadate compounds were investigated, where the vanadates included chloride vanadates (M^II₂VO₄Cl), pyrovanadates (M^II₂V₂O₇), orthovanadates (M^II₃(VO₄)₂) with divalent cations M^II of Mg, Sr, Ba, and Zn, and oxofluorovanadates (A^IVOF₄) with an alkali metal A^I. A chloride pyrolysis method and a liquid phase precipitation method were proposed for preparing the chloride vanadates and pyro‐ and orthovanadates, respectively. These vanadate compounds showed self‐activated photoluminescence (PL) based on the VO₄ clusters against the ultraviolet (UV) light irradiation. The colors of PL covered almost the whole visible‐light region from blue to yellow as Sr₂VO₄Cl (deep blue), Ca₂VO₄Cl (sky blue), Ba₂V₂O₇ (green), Sr₂V₂O₇ (yellowish green), Zn₃(VO₄)₂ (yellow), and Mg₃(VO₄)₂ (yellow). A correlation was suggested from these compounds between the luminescent colors and the structural feature as the longer V–O distances in the VO₄ tetrahedra in the crystal structures led to the longer wavelength in PL. This seemed to be also applicable for the oxofluorovanadates A^IVOF₄ (A^I = K and Cs) which contain the VOF₄ polyhedra with one O^2? ion and four F^‐ ions as the ligands, as they exhibited the reddish PL.     

Novel Visible Emission and Mechanism Investigation from PbS Nanoclusters‐Doped Borosilicate Glasses

Borosilicate glasses doped with PbO, ZnS, or PbS were fabricated to investigate the visible emissions (one located at 370 nm and another at 550 nm) observed in the PbO and ZnS codoped glass. Several series of glassy systems were designed to investigate the mechanism of above visible emissions. The absorption, photoluminescence (PL), photoluminescence excitation (PLE) spectra, and lifetime measurements were used to characterize all the emissions. The nanosecond level lifetimes for all the samples' 370 nm emissions ascribed the 370 nm emission to the glass defects. Measured lifetimes for the PbS quantum dots (QDs) in the glasses with an emission in the near‐infrared region which was about 8 μs was close to the values for the yellow emission, which confirmed the formation of PbS nanoclusters in the codoped glass was responsible for the yellow emission.     

Low‐Temperature Magnetic and Dielectric Anomalies in Rare‐Earth‐Substituted BiFeO3 Ceramics

In this work, we report on the magnetic and dielectric anomalies observed in dense Bi_1–xRE_xFeO₃ ceramics (RE = Dy, Tb; 0 ≤ x ≤ 0.3) at cryogenic temperatures. For compositions with a high content of rare‐earth ions, thermomagnetic experiments revealed a distinct anomaly in the magnetization curves at temperatures below 200 K. The temperature of the magnetic anomaly along with a thermal hysteresis was found to be dependent on the rare‐earth concentration and magnetic field strength. Low‐temperature dielectric measurements showed an anomalous relaxor‐like behavior of the relative permittivity and dielectric loss in highly doped ceramic samples. The anomalies in low‐temperature magnetization and dielectric response are suggested to result from the presence of GdFeO₃‐like orthoferrite phase and/or bismuth rare‐earth‐mixed iron garnet impurities.     

Molecular Dynamics Simulation of the Structure of Borate Glasses

The structures of borate glasses have been simulated by use of molecular dynamics. A new type of potential calculated by means of the intermediate neglect of differential overlap (INDO) method and a three-body potential were introduced into the molecular dynamics simulation. Boroxyl rings and diborate groups have been successfully reproduced in the structure models obtained from the present molecular dynamics simulation. Calculated radial distribution functions agreed well with the observed one obtained from X-ray diffraction data. The distribution of O–B–O and B–O–B bond angles is also given.     

Effect of CeO2 on the Glass Structure of Sodium Germanate Glasses

Germanate glasses have potential applications as optical fibers. Materials doped with rare earth ions are good candidates for optical, lasing, and magnetic applications. Based on the ternary system, CeO₂–Na₂O–GeO₂ a series of six glasses were fabricated using powder fusion, and varying the Na₂O content from 0 to 45 mol%, and a CeO₂ content constant at 3 mol%. The glasses were analyzed by FT‐IR, Raman and X‐ray photoelectron (XPS) spectroscopies to obtain information about the glass structure, cerium oxidation's state and how it is introduced in the glass network. FT‐IR and Raman spectra revealed the presence of GeO₆ and GeO₄ groups as well as Q² and Q³ units in the glasses with alkali low content. XPS spectra analysis revealed that the cerium ions were reduced from Ce⁴⁺ to Ce³⁺. The nonbonding to total oxygen ratio was estimated from the curve fitting of the O 1s core level spectra. Density and elastic parameters showed a nonlineal tendency in the change of the physical properties as a function of Na₂O content. Finally, photoluminescence spectroscopy confirmed the presence of Ce³⁺ ions. The characteristic 4f → 5d electronic transitions at 360 nm were detected, when a 280 nm excitation line of pulsed laser was used as excitation source.     

氧化物掺杂对磷酸盐低熔点玻璃结构与封接性能的影响

制备了以ZnO-B2O3-P2O5为基体,外加金属氧化物(Fe2O3, MnO2, CuO和 TiO2)的玻璃试样,研究了金属氧化物对玻璃膨胀系数、密度、玻璃转变温度、软化点温度、化学稳定性、电阻率的影响.实验结果表明外加金属氧化物Fe2O3对提高玻璃的化学稳定性最为有效,MnO2不仅在提高磷酸盐玻璃的化学稳定性方面效果优异,同时在降低玻璃的封接温度方面效果明显,CuO、TiO2对封接性能的影响介于上述二者之间.通过扫描电镜、红外光谱分析了玻璃结构的变化.     

Optical and Electrical Properties of Nd3+ Doped TeBiY Borate Glasses

60B₂O₃-30Bi₂O₃-5TeO₂-(5–x)Y₂O₃-xNd₂O₃ mole% (0 ≤ × ≤ 4) glasses were prepared by the usual experimental glass-melting procedures. This work was carried out to study the effect of Nd₂ O ₃ on the properties of the glasses studied and thereby their structure. The effect of the replacement of Y₂O₃ by Nd₂O₃ on the optical and electrical properties of the glass samples was studied. The results obtained showed that the values of density, oxygen packing density, concentration of Nd ions and field strength were found to increase with increase of the Nd₂O₃. On the other hand the molar volume, inter-nuclear distance and polaron radius showed the opposite behavior with increasing Nd₂O₃ content. The results also showed that the direct and indirect optical band gap were found to increase which indicate that increasing the concentration of Nd₂O₃ leads to a change in the structure of glasses induced by Nd₂O₃. Dc and ac conductivities values were found to increase, whereas the dc activation energy decreases, with increasing Nd₂O₃ concentration. An increase in the dielectric constant values with increasing Nd₂O₃ content is observed. The results suggest that the CBH model seems to be the appropriate model for the ac conductivity in the studied glasses.

     

Thermal Expansion of Binary Borate Glasses and Their Structure

The possible structural transformations in binary borate glasses are analyzed by comparing the phase diagrams and the data available in the literature on the thermal expansion of glasses.     

Structure and Nonlinear Optical Properties of Lanthanide Borate Glasses

The third–order nonlinear optical susceptibility, χ⁽³⁾, of lanthanide (lanthanum, praseodymium, neodymium, and samarium) borate glasses has been measured by the third harmonic generation method. The structure of the present glass system has been studied by infrared and Raman spectroscopic methods. The network structures of the present Ln₂O₃–B₂O₃ glasses have been confirmed to be basically similar to each other. Praseodymium, neodymium, and samarium borate glasses exhibit χ⁽³⁾ values that are larger than lanthanum borate glasses, because of the optical resonance effect, in accordance with the f – f transition. Especially, the χ⁽³⁾ value for 30Pr₂O₃·70B₂O₃ glass is 1.8 × 10⁻¹² esu, which is a factor of ∼60 larger than that of SiO₂ glass. This striking enhancement of χ⁽³⁾ is mainly attributed to the large transition moment to the first excitation state.     

Study of the Structure of Iron-Containing Zinc Borate Glass

The results of the experimental study of glass of the xFe₂O₃–(100–x)[40ZnO. 60B₂O₃] composition in which the content of iron oxide varies from 0 to 10 mol % are presented. The regularities of the glass structure change in the short- and intermediate-range order structures are considered based on the data of infrared spectroscopy and Raman spectroscopy. The valence and coordination state of iron in a glass matrix is studied by Mössbauer spectroscopy.     

Optical Study of Lithium–Bismuth–Borate Glasses

Glasses with compositions x Bi₂O₃(75− x )B₂O₃25Li₂O₃ for 0≤ x ≤40 mol% have been prepared using the normal melt-quenching technique. The optical absorption and reflection spectra were recorded at room temperature in the wavelength range 190–1100 nm. From the absorption edge studies, the values of the optical band gap ( E _opt) and Urbach energy (Δ E ) have been evaluated. Optical parameters such as refractive index and complex dielectric constant have been determined. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Color parameters and color difference data L ^*, U ^*, V ^*, C ^*, h _ue, W , Y _e, Δ L ^*, Δ U ^*, Δ V ^*, Δ C ^*, and Δ E have been calculated.     

Vitrification, Properties, and Structure of Lead-Tellurite Borate Glasses

The vitrification, structure, and physicochemical properties of glasses in the PbO – ZnO – B₂O₃ – TeO₂ system are studied. The dual role of the lead ions in the glass structure is confirmed. It is demonstrated that the coordination transition of boron ions correlates with the concentration of PbO in glass. A nonlinear dependence of properties on the glass composition is due to the structural modifications in glass.