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In this paper, the possibility of retreated lithium slag (RTLS) with a high content of alkali, sulfate and fluoride as a partial replacement for fly ash (FA) to produce autoclaved aerated concrete (AAC) was investigated. The influence of the RTLS dosage on the AAC performance were examined. The composition and microstructure of hydrates as well as the microstructure of the RTLS-FA-based AAC compositions were determined by XRD, FTIR, TG-DSC and SEM. The results illustrated that the incorporation of RTLS changed the crystal structure and the microstructure of the tobermorite. With increased RTLS contents, the morphology of tobermorite was changed, and the grass-like tobermorite gradually transformed into network-like tobermorite. The newly formed tobermorite improved the mechanical performance of the AAC. Compared with the RTLS10, the content of tobermorite in the RTLS30 increased by 8.6%. [ABSTRACT FROM AUTHOR]

Recently, we have demonstrated a method to record the longitudinal phase-space distribution of a pulsed cryogenic buffer gas cooled beam of barium fluoride molecules with high resolution. In this paper, we use this method to determine the influence of various source parameters. Besides the expected dependence on temperature and pressure, the forward velocity of the molecules is strongly correlated with the time they exit the cell, revealing the dynamics of the gas inside the cell. Three observations are particularly noteworthy: (1) The velocity of the barium fluoride molecules increases rapidly as a function of time, reaches a maximum 50–200 µ s after the ablation pulse and then decreases exponentially. We attribute this to the buffer gas being heated up by the plume of hot atoms released from the target by the ablation pulse and subsequently being cooled down via conduction to the cell walls. (2) The time constant associated with the exponentially decreasing temperature increases when the source is used for a longer period of time, which we attribute to the formation of a layer of isolating dust on the walls of the cell. By thoroughly cleaning the cell, the time constant is reset to its initial value. (3) The velocity of the molecules at the trailing end of the molecular pulse depends on the length of the cell. For short cells, the velocity is significantly higher than expected from the sudden freeze model. We attribute this to the target remaining warm over the duration of the molecular pulse giving rise to a temperature gradient within the cell. Our observations will help to optimize the source parameters for producing the most intense molecular beam at the target velocity. [ABSTRACT FROM AUTHOR]

The bandwidth adaptation factor (BAF), which is calculated as BW • (λ L - λ H): (d • f r), is a crucial evaluation parameter for designing ultrathin broadband absorbers. In this paper, a high BAF absorber is designed by utilizing an impedance frequency selective surface (FSS), which includes a six pinnacles FSS, a La-doped mullite ceramic dielectric layer and a metal backplane. The optimal numbers of pinnacled FSS is determined through comparison and optimization, and the power monitor results indicate that the main loss modes are electrical and ohmic loss. Subsequently, the impedance analysis reveals that the favourable absorption performance is attributed to good impedance matching and high loss coefficient. Furthermore, the observation of the current distribution on the surface confirms that the primary loss appears at the pinnacles. The proposed absorber has below −10 dB reflectivity in 12.26–18.00 GHz. Meanwhile, the BAF is 3.36 and the thickness is only 0.061 λ L (1.5 mm). The measured results are in good agreement with the simulation results, demonstrating an excellent BAF characteristic. [ABSTRACT FROM AUTHOR]

In this paper, Er3+ doped TeO 2 -ZnF 2 -BaF 2 -KF-Ta 2 O 5 tellurite glasses with low hydroxyl content (∼0.03 × 10−19 cm−3) were investigated employing both glass composition and glass melting process optimization. The Raman spectra and physical properties were characterized to analyze the structure of the glasses. Under the pumping of 980 nm LD laser, intense up-conversion fluorescence at 1.5 and 2.7 μm of samples and their lifetimes were detected and analyzed, and the related transition mechanisms with gradient-varying Er3+ doping concentrations were discussed. The maximum absorption and emission cross section at 2.7 μm was calculated to be 6.4 × 10−21 cm2 and 6.8 × 10−21 cm2, correspondingly, which were higher than those of traditional tellurite glasses. Using the calculated and measured spectroscopic parameters of bulk tellurite glass, a dual-wavelength pumping model was established to verify the feasibility of mid-infrared laser output in similar tellurite glass fiber. Experimental results support the assertion that the Er3+ doped tellurite glasses hold promise as a candidate laser gain medium for mid-infrared fiber laser systems. [ABSTRACT FROM AUTHOR]

In this work, we present the results of the analysis performed with near edge absorption fine structure spectroscopy of barium edges in a B+BaF2 optical filter. The radiation was generated by a laser-plasma soft X-ray source based on a double-stream gas puff target. The use of a flat-field spectrometer based on a diffraction grating allowed us to collect the absorption spectra of the radiation transmitted by the analyzed optical filter. The results demonstrate the appearance of clear M-edges of barium (M4 and M5). [ABSTRACT FROM AUTHOR]

We present sub-50 fs soliton pulse generation from a diode-pumped Kerr-lens mode-locked laser based on an Yb3+-doped BaF2 crystal. Utilizing a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:BaF2 laser generates pulses as short as 46 fs at 1060.1 nm with an average output power of 45 mW at a pulse repetition rate of ~65.6 MHz via soft-aperture Kerr-lens mode locking. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation of the Yb:BaF2 crystal, as well as the shortest pulse duration ever achieved from any diode-pumped mode-locked laser based on an Yb3+-doped alkaline-earth fluoride crystal. [ABSTRACT FROM AUTHOR]

A series of CoCrFeNiMn high-entropy alloy matrix self-lubricating composites were prepared by spark plasma sintering. The composites are composed of an FCC phase, Cr7C3, Ag, and eutectic fluoride BaF2/CaF2 phases. The microstructure of the composites is uniform. The additional phases distribute along the boundary of equiaxed grains of the FCC phase. The compressive yield strength and fracture toughness decrease with the increase of eutectic fluoride BaF2/CaF2. The composites are susceptible to brittle cleavage fracture. [ABSTRACT FROM AUTHOR]

This paper examines how the transformation of BaF from a single-crystalline to polycrystalline state as a result of uniaxial hot-forming influences its properties. With increasing strain, the microstructure of the material changes from a nonuniform polycrystalline one, with a block size of about 1 mm, to a classic ceramic structure made up of grains in which dislocations form walls, resulting in a subgrain structure. The best mechanical characteristics are offered by the ceramic produced at a strain on the order of 700%. The intensity of the fast X-ray luminescence component (band at 220 nm) is independent of strain, whereas that of the slow component (band at 310 nm) decreases with increasing strain. [ABSTRACT FROM AUTHOR]

Ternary oxides containing Sn2+ are rare and difficult to prepare using solid state reaction due to disproportionation of Sn2+ at high temperature. In this paper, nanoparticles of barium titanate doped with different amounts of Sn2+ consisting of single phase perovskite structure were successfully synthesized for the first time by using a microwave-assisted solvothermal reaction. The particle sizes were about 20–40 nm in diameter and increased with increasing the amount of doped tin. Solidified ceramic bodies were obtained using a spark plasma sintering method under argon atmosphere avoiding the disproportionation and oxidation of Sn2+ in the air. The grain size and dielectric constant of the sintered body decreased with increasing the amount of doped tin. [ABSTRACT FROM AUTHOR]

Coated-conductor applications of YBCO require YBCO layers with high Jc and a thickness of several micrometers. The barium fluoride process offers a convenient way of depositing crack-free fluorinated precursor layers up to 5 microns thick. However, converting thick precursor layers into c-axis-oriented YBCO flints is challenging due to extensive nucleation of random grains. In this paper we address this problem with both a theoretical and experimental analysis of YBCO nucleation. We utilized optical polarization contrast to observe YBCO nuclei imbedded in the precursor matrix. We observed that the nuclei density strongly depends on processing parameters, with the oxygen partial pressure being one of the strongest factors. During ex-situ processing the nuclei merge and form grains and the nuclei density is, therefore, directly related to the grain size of YBCO film. It is desirable to have a small grain structure, since large grains do not connect well and the Jc of such a film is low. However, attempts to increase the nuclei density also generates more randomly oriented grains. Therefore the optimization of ex-situ processing is essentially finding a balance between c-axis grain density and random grain content. [ABSTRACT FROM AUTHOR]

Single-phase samples of the Ba1−xCexF2+x solid solution (x = 0.3–0.4) were synthesized by directional crystallization in the form of single crystals and by co-precipitation from aqueous nitrate solutions using potassium fluoride as a fluorinating agent in the form of nanopowders. The cathodoluminescence of the pressed powder samples was studied in comparison with the BaF2: Ce single crystals in 250–460 nm (2.7–5 eV) spectral range upon excitation by an electron accelerator. The cathodoluminescence spectra of the samples revealed a wide band in the range of 3.0–4.0 eV, which consists of two typical components of Ce3+ with decay time 23 ns in the case of single crystals and three decay times 27 ns, 140–170 ns, and ~600 ns in the case of pressed powders. The decay time of the short-wavelength component (27 ns) in the case of pressed powders is close to the lifetime of the excited state of the Ce3+ ion. The developed X-ray phosphors can be applied for embedding in diamonds for diamond–nanoparticle composite preparation. [ABSTRACT FROM AUTHOR]

Organic–inorganic composite scintillators, demonstrating advantages of easy large-area preparation and a high detection efficiency, have shown enormous potential application prospects in radiation detection and imaging. In this study, bulk polystyrene (PS) composite scintillators were successfully prepared by embedding inorganic BaF2 particles with a loading amount of up to 80 wt% during the polymerization process of the plastic scintillator. The inorganic BaF2 particles were uniformly dispersed in the organic matrix. With the increase of the loading amounts of BaF2 particles, the X-ray-excited luminescence intensity of the PS-BaF2 composite scintillators was about eight times higher than that of the commercial pure plastic scintillator. The scintillation counts under the gamma ray (59.5 KeV) irradiation also showed that the detection efficiency was obviously enhanced by BaF2 particle loading. More importantly, their scintillation pulse retains the decay kinetics of the organic matrix without loading the slow-decay component of BaF2. This work provides a promising solution for the application of the PS-BaF2 composite scintillator in high-efficiency radiation detection and large-area imaging. [ABSTRACT FROM AUTHOR]

Based on the literature data, the most used chemical element for the removal of the contaminant fluoride ions from different water systems was the Al followed by the Zr, Mg, Fe, C, and several others elements that form stable Me–F complexes. The application of mixed composite adsorbents is a modern tendency, but in this study, the dry aluminum sulfate was tested for direct chemical elimination of the fluoride ions from real industrial zinc sulfate electrolytes. The behavior of the used fluorine ion-selective electrode (FISE) was tested in the presence of sodium fluoride and aluminum sulfate. For suppression of the negative role of the aluminum ions on the FISE potential citrate total ionic strength adjustment buffer (TISAB) was used for appropriate ex situ analytical measurements of the fluoride ions in the real zinc electrolytes from the different hydrometallurgical purification stages. The elimination of the free fluorine ions was tested at room temperature (18–27 °C) and by heating up to 40 °C. The obtained results show that at room temperature, the efficiency of the reaction between F− and Al3+ ions was not very satisfied. Maximum 13% from the initial fluoride concentration was reduced at real conditions. By heating the process was intensified up to 75–95%, but in excess of non-reacted aluminum ions that additionally contaminated the electrolyte for zinc electrowining. The experimentally proven advantages and disadvantages revealed that the elimination reaction needs further optimizations before any applications at plant conditions. Factors as temperature was beneficial, whereas pH was hard for operation since the dry aluminum sulfate acidified the plant electrolytes and the zinc sulfate matrix precipitated easy by titration from acid to neutral conditions. [ABSTRACT FROM AUTHOR]

Barium lanthanum fluoride powders have been prepared by reacting barium nitrate and lanthanum nitrate in molten sodium nitrate at 350 and 450°C, using a sodium fluoride as a fluorinating agent. A fivefold excess of sodium fluoride has been shown to prevent pyrohydrolysis. We have identified a phase of variable composition with the fluorite structure, Ba1–xLaxF2+x (0.3 < x < 0.5), which has high ionic conductivity (2.3 × 10–4 S/cm at 500 K) and an activation enthalpy for ionic transport of 0.50 ± 0.01 eV. [ABSTRACT FROM AUTHOR]

Four-wave mixing processes are ubiquitous in ultrafast optics and the determination of the coefficients of the χ(3) tensor is thus essential. We introduce a novel time-resolved ultrafast spectroscopic method to characterize the third-order nonlinearity on the femtosecond time-scale. This approach, coined as "nonlinear chirped interferometry," makes use of the variation of the optical group delay of a transmitted probe under the effect of an intense pump pulse in the nonlinear medium of interest. The observable is the spectral interference between the probe and a reference pulse sampled upstream and the metric is the transient swing of the probe group delay. We show that the detected signal is enhanced when the pulses are weakly chirped, and that, although interferometric, the method is intrinsically less sensitive to environmental phase fluctuations and drifts. By chirping adequately the reference pulse, the transient frequency shift of the probe pulses is also detected in the time domain and the detected nonlinear signal is enhanced. Nonlinear phase shifts as low as 10 mrad, corresponding to a frequency shift of 30 GHz, i.e., 0.01% of the carrier frequency, are detected without heterodyne detection or active phase-stabilization. The diagonal and/or non-diagonal terms of reference glasses (SiO2) and crystals (Al2O3, BaF2, CaF2) are characterized. The method is finally applied to measure the soft vibration mode of KTiOAsO4 (KTA). [ABSTRACT FROM AUTHOR]

The effect of BaF2, MgF2, and AlF3 on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]4 and [GeO]6 units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF2. The 27Al MAS NMR spectrum of BGG glass with AlF3 suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the 4I13/2→4I15/2 transition of Er3+ ions increases in the BGG + MgF2 glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties. [ABSTRACT FROM AUTHOR]

A cross polarized wave (XPW) generation experiment with double BaF2 crystals in air was demonstrated with 120 µJ input pulse. A circular aperture was used to truncate the near field profile of the input beam and remove the outer part of the beam, and circularly symmetric beam profiles were generated at the BaF2 crystal positions. The measured focal spot size was close to the diffraction limit, and the energy stability of XPW was improved from ∼1.89% (without the aperture) to ∼0.67% (with the aperture). [ABSTRACT FROM AUTHOR]

Single crystals of Ca1– хBaхF2 (x = 0.001–0.05 and 0.85–0.99) solid solutions have been grown by the Bridgman method, and their thermal conductivity has been measured in the range 50–300 K by an absolute steady-state axial heat flow technique. The thermal conductivity of all samples has been shown to decrease with increasing temperature. At 300 K, the lowest thermal conductivity of the samples with x ≤ 0.05 exceeds 6 W/(m K), and that of the samples with x ≥ 0.85 is a factor of 2 lower. [ABSTRACT FROM AUTHOR]

Featured Application: laser surface-processing. Monocrystalline barium fluoride (BaF2) slab targets were irradiated by focused 46.9-nm laser radiation at various fluence levels above the ablation threshold. Well-developed ablation patterns with sharp edges were studied by AFM (atomic force microscopy). Their inner surfaces were uniformly covered by periodic structures. The spatial period of the ripples depends on the laser fluence. When the sample is rotated by 45°, the orientation of the grating-like structure changes accordingly. Thus, the grating vector of the periodic structure seems to be coupled to the crystallographic planes of the single crystal. This means that the XUV-laser induced ripples reported here differ from LIPSS (laser-induced periodic surface structures) associated with interference phenomena occurring on illuminated surfaces. Therefore, other mechanisms are discussed to explain the formation of the periodic nanostructures reported in this article. [ABSTRACT FROM AUTHOR]

Barium fluoride (BaF2) crystals are attracting much attention as efficient inorganic scintillator promising for high‐energy physics, industrial inspection, and other fields because of the fast component of the decay time (0.6 ns) and high radiation resistance. However, two major drawbacks limit its practical application: (i) a slow decay time of ~600 ns is derived from self‐trapping excitons; (ii) the absolute light yield from the fast luminescence component is not competitive. The introducing of rare earth ions and preparation of BaF2 polycrystalline ceramics is considered to be effective measures to solve these bottlenecks. Pr3+ is extremely suitable as the activated ion of scintillation materials, which possess emission peaks located in visible band and the faster 5d–4f transition. In this work, highly sinterable Pr3+:BaF2 precursor powder was synthesized via the coprecipitation method by adjusting the reactant concentration and temperature. The morphology and microstructure of as‐synthesized powders were characterized using scanning electron microscopy (SEM) and transmittance electron microscopy analysis. The 5 at.% Pr3+:BaF2 transparent ceramic with a transmittance of 50.7% at the wavelength of 500 nm was fabricated by hot pressing the as‐prepared powders at 900°C for 4 h under the axial pressure of 50 MPa. The SEM images of ceramic cross‐section show that the residual pore is the main light scattering source. The absorption and emission spectrum of ceramic samples were discussed. [ABSTRACT FROM AUTHOR]

• A simultaneous denitrification and biogas desulfurization process (SDBD) was proposed. • 0.9%–1.5% hydrogen sulfide in biogas was completely removed. • More than 85% COD, 98% NH 4 +-N and 81.65% TN was removed from real domestic sewage. • Hydrogen sulfide introduction altered the pathway of nitrate removal. • Economic assessment enables SDBD system to be a promising way in biological N removal. This paper proposed a novel simultaneous denitrification and biogas desulfurization (SDBD) process for domestic sewage treatment and biogas upgrading. The process consisted of an expanded granular sludge bed (EGSB) for integrated autotrophic and heterotrophic denitrification (IAHD) and a biological aerated filter (BAF) for nitrification. The experiments were firstly conducted to investigate the performance of the lab-scale SDBD system with real domestic sewage at various hydraulic retention times (HRT). The system successfully achieved 83.0 ± 1.8% chemical oxygen demand (COD), 96.2 ± 1.8% ammonia (NH 4 +-N) and 67.3 ± 4.1% total nitrogen (TN) removal efficiency without biogas introduction, and the optimal HRT of EGSB and BAF was determined to be 6 h and 4 h, respectively. Then, biogas with three different hydrogen sulfide concentrations (1.5%, 1.2% and 0.9%) was introduced into the system. Almost complete removal of hydrogen sulfide in biogas was achieved in all the tested scenarios and the removal efficiency of COD, NH 4 +-N and TN maintained at around 86.8%, 98.4% and 83.4%, respectively. Microbial community analysis results showed that biogas introduction notably increased the bacterial diversity and particularly enriched the nitrate-reducing, sulfide-oxidizing bacteria, which forms the major contribution to the hydrogen sulfide removal in the system. Finally, we put the SDBD system in the whole treatment system of domestic sewage and discussed its economics. The results indicated that the total operating cost of sewage treatment plant could be saved to 0.59 RMB/m3, which proved SDBD system to be a promising alternative way in biological nitrogen removal and biogas desulfurization. [ABSTRACT FROM AUTHOR]

We report a study of upconversion luminescence in BaF2–HoF3 crystals in the visible spectral region under excitation to the 5I5 level of Ho3+ ions by laser radiation with a wavelength of 890 nm. For these excitation conditions, we propose mechanisms responsible for upconversion luminescence from the 5F3, 5S2(5F4) and 5F5 levels of Ho3+ ions. [ABSTRACT FROM AUTHOR]

We have prepared glasses in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) and HfF4–BaF2–LaF3–AlF3–NaF (HBLAN) systems in which fluorine anions are partially replaced by chlorine and bromine anions. Structural changes in the chlorine-substituted glasses have been investigated by Raman spectroscopy and their crystallization behavior has been studied by differential thermal analysis and X-ray diffraction. The results demonstrate a characteristic decrease in glass transition temperature (Tg) and the precipitation of fine-particle crystalline chloride and bromide phases in a temperature range well below the crystallization temperature (Tx) of the fluoride analogues. We have identified phases that crystallize during heat treatment of the glasses at various temperatures. [ABSTRACT FROM AUTHOR]

Lead telluride films have been grown on Si (100) and BaF2 (100) substrates by a modified hot-wall method using a graphite reaction chamber. According to X-ray diffraction, X-ray microanalysis, and scanning electron microscopy characterization results, the average growth rate of PbTe films having compositions within the homogeneity range of lead telluride increases with increasing lead vapor partial pressure and decreases with increasing tellurium vapor partial pressure, independent of the nature of the substrate. The rate of PbTe film growth has been shown to be maximal in the initial stage of the process and decrease monotonically over time, independent of the nature of the substrate. Independent of the growth time, the average growth rate of the PbTe films on the Si (100) substrates is considerably higher than that on the BaF2 (100) substrates. Reflection high-energy electron diffraction data indicate that the texture of the PbTe films on Si (100) corresponds to the substrate orientation and that the misorientation angle of the mosaic blocks does not exceed 20°. On the BaF2 (100) substrates, we observe epitaxial PbTe film growth with the orientation relationship (100), [011] PbTe ║ (100), [011] BaF2. [ABSTRACT FROM AUTHOR]

Well defined and photoluminescent BaLaF:Eu, BaLaF:Eu/Tb and BaLaF:Eu@BaLaF:Gd core/shell nanoplates were synthesized via facile hydrothermal method. X-ray powder diffraction, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, Fourier transform infrared spectrum, photoluminescence, kinetics of luminescence decay and magnetic studies were used to characterize the structural, optical and magnetic properties of these nanoplates. TEM images show that these nanoplates have pseudo spherical shape with the average crystallite size of 14-21 nm. Down-conversion luminescent properties of doped BaLaF nanoplates were investigated and impact of core/shell formation and co-doping has been explored. The luminescent intensity and lifetime of Eu in Eu/Tb co-doped BaLaF nanoplates and BaLaF:Eu@BaLaF:Gd core/shell nanoplates are enhanced with respect to the bare BaLaF:Eu nanoplates. Coating BaLaF:Eu core with BaLaF:Gd shell on the surface reduces defects on the surface of core and so the surface quenching is suppressed, thus reducing the efficiency of nonradiative decay pathways. In the case of Eu/Tb co-doped BaLaF nanoplates, energy transfer process from Tb to Eu enhanced the luminescent intensity of Eu ion. Also the Gd doped BaLaF core/shell nanoplates exhibit weakly ferromagnetic interactions with coercivity value of 418.96 G at room temperature. [ABSTRACT FROM AUTHOR]

A ceramic 2-µm laser beam visualizer based on Ho-doped β-BaZrF is proposed. The ceramic has been prepared by crystallizing 60ZrF-35BaF-5BiF glass doped with 3 wt % HoF. Exciting the Ho I level by a Tm:LiYF (Tm:YLF) laser at λ = 1910 nm, we observed a strong red luminescence, due to the F → I transition, and a weaker, green luminescence, corresponding to the ( F, S) → I transition. The threshold power density of the Tm:YLF laser at which a red spot was observed on a ceramic sample was 1.1 W/cm. [ABSTRACT FROM AUTHOR]

We have prepared glasses and semicrystalline phases with a green color in the systems ZrF(53.5)-NaF(20)-BaF(20)-LaF(6.5 − x)-YbF( x) (0 ≤ x ≤ 6.5 mol %) (I) and ZrF(53.5)-NaF(20)-BaF(20 − x)-LaF(6.5)-YbF( x) (0 ≤ x ≤ 20 mol %) (II). Thermal analysis results demonstrate that, in both systems, the glass transition temperature of the samples containing ≤3 mol % YbF lies in the range 200-250°C, their heating curves show two or three crystallization events (at 320-340, 380-460, and 415-490°C), and their melting points range from 460 to 490°C. Increasing the YbF content of the glasses to 4 mol % and above (system I) has no effect on their glass transition temperature, reduces the temperature of the first crystallization event from 340 to 305°C, and produces extra peaks in the range 545-600°C, above the major melting peak, which can be accounted for by a nonequilibrium state of the glasses. Ytterbium difluoride substitution for barium difluoride (10 to 20 mol %) (system II) leads to the formation of semicrystalline phases and increases the glass-transition (305°C), crystallization (470-515°C), and melting (570-690°C) temperatures. The IR spectra of such samples show, in addition to a so-called 'featureless continuum' (∼500 cm), absorption bands characteristic of the Yb-F bond. Electronic spectra also confirm that the glasses contain both divalent and trivalent ytterbium. [ABSTRACT FROM AUTHOR]

A lead salt mid-infrared laser sample grown by molecular-beam epitaxy (MBE) on a polished BaF2 (110) substrate is studied. For improving the laser performance at higher operating temperature, a method of substrate transfer from a BaF2 substrate to a copper heat sink is developed. The cleaved facet along the {100} plane, which is helpful for the formation of a Fabry-Pérot resonant cavity on the laser sample, is observed. Pulsed photoluminescence measurements are conducted on the laser sample step by step during processing in order to trace the effect of each process step. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of multicolor light-emitting nanomaterials based on rare earths (RE3+) are of great importance due to their possible use in optoelectronic devices, such as LEDs or displays. In the present work, oxyfluoride glass-ceramics containing BaF2 nanocrystals co-doped with Tb3+, Eu3+ ions were fabricated from amorphous xerogels at 350 °C. The analysis of the thermal behavior of fabricated xerogels was performed using TG/DSC measurements (thermogravimetry (TG), differential scanning calorimetry (DSC)). The crystallization of BaF2 phase at the nanoscale was confirmed by X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM), and the changes in silicate sol–gel host were determined by attenuated total reflectance infrared (ATR-IR) spectroscopy. The luminescent characterization of prepared sol–gel materials was carried out by excitation and emission spectra along with decay analysis from the 5D4 level of Tb3+. As a result, the visible light according to the electronic transitions of Tb3+ (5D4 → 7FJ (J = 6–3)) and Eu3+ (5D0 → 7FJ (J = 0–4)) was recorded. It was also observed that co-doping with Eu3+ caused the shortening in decay times of the 5D4 state from 1.11 ms to 0.88 ms (for xerogels) and from 6.56 ms to 4.06 ms (for glass-ceramics). Thus, based on lifetime values, the Tb3+/Eu3+ energy transfer (ET) efficiencies were estimated to be almost 21% for xerogels and 38% for nano-glass-ceramics. Therefore, such materials could be successfully predisposed for laser technologies, spectral converters, and three-dimensional displays. [ABSTRACT FROM AUTHOR]

A BaF(p-BDC)0.5 catalyst was prepared by solid state reaction at room temperature with Ba(OH)2 as precursor, NH4F as F source, and H2(p-BDC) as organic ligand. The calcined samples were used as catalysts for dehydrochlorination of 1-chloro-1,1-difluoroethane to generate vinylidene fluoride (VDF) at 350 °C. Commercial production of VDF is carried out at 600–700 °C. Clearly, pyrolysis of the BaF(p-BDC)0.5 catalyst provided a promising way to prepare VDF at low temperatures. Prior to calcination, the activity of the BaF(p-BDC)0.5 catalyst was low. Following calcination at high temperatures, BaF(p-BDC)0.5 decomposed to BaF2 and BaCO3, and then the catalyst was chlorinated and fluorinated to BaClF, which showed high activity and stable VDF selectivity for dehydrochlorination of 1-Chloro-1,1-Difluoroethane to VDF. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM), reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) are used to characterize the microstructure and surface topography of YBa[sub 2]Cu[sub 3]O[sub 7-x] (YBCO) films. The YBCO films of approximately 0.2 and 0.8 µm thickness are prepared by a postannealing of precursor films of co-evaporated Y, BaF[sub 2] and Cu. The annealing conditions are the same for all cases except for the temperature elevation rate. RHEED patterns corresponding to the YBCO structure are observed in both the samples after annealing at 700°C for 30 minutes. The XRD patterns show that both YBCO films have primarily c-axis orientation. According to TEM observation results, the YBCO film of 0.2 µm thickness is epitaxially grown from a substrate surface. In the case of thicker films of 0.8 µm, the bottom region of the film is epitaxial YBCO, while the top region is a mixture of a-axis orientation, other orientations and impurities. [ABSTRACT FROM AUTHOR]

The thermal expansion of the CaYF, CaYbF, CaCoF, BaLaF, and BaNdF solid solutions has been studied experimentally from below liquid-nitrogen temperature to room temperature. The results demonstrate that both the iso- and heterovalent dopants have a weak effect on the linear thermal expansion coefficient of the fluorite-structure crystals. [ABSTRACT FROM AUTHOR]

It is well known that the optimization of the basic properties of materials is related not only to changes of the substance of the material itself, but can also predict the change of their surface. In this regards, the search for, and study of, new nanostructured coatings based on the laser deposition method becomes extremely promising. Here, we used a laser-oriented deposition technique in order to place carbon nanotubes in a vertical position on the BaF2 surface to modify it. Such modification affected the increasing material transparency, connected with a decrease of the reflection via change the Fresnel losses; hydrophobicity and microhardness as well. Characteristics of the obtained material were studied via spectral analysis, AFM-method, wetting-angle measurements, microhardness estimations to support the possible covalent bonding between the carbon atoms and the interface materials atoms. Moreover, the quantum–chemical calculations completely confirmed the experimental results of the changes of electronic properties of BaF2 substrate after deposition of the CNTs. As the results novel optimized structure based on BaF2 is presented to be used in general optoelectronics, cosmos and laser technique as well. [ABSTRACT FROM AUTHOR]

Some coated conductor applications require a YBCO layer at least 5 µm thick with high J[sub c]. The growth of thick c-axis oriented epitaxial layers using the barium fluoride ex-situ technology is not always possible. Films over 3 µm thick have more undesirable a-oriented and random grains than thinner ones. We present an analysis of thick film nucleation and conclude that thick precursor layers impede out-diffusion of the ex-situ reaction product, HF. High impedance for HF diffusion results in large variations of the chemical potential of the growth reaction and disruption of the nucleation process. We conclude that a solution for c-axis growth is control of the precursor permeability. A method is described for controlling the permeability of precursor layers. Using this technique we were able to grow c-axis oriented 5-µm thick films on oxide-buffered Ni tape with J[sub c](0 T) = 4 × 10[sup 5] A/cm² and J[sub c](1 T) = 8 × 10[sup 4] A/cm². [ABSTRACT FROM AUTHOR]