BaF2 CaF2 Research Articles

Impact of the O/P ratio on the optical properties and structures of fluoride–phosphate glass

AbstractCa(PO3)2–AlF3–CaF2–BaF2–BaO glasses were prepared by the melt quenching method, and the effects of the O/P ratio on the optical properties and glass structure were investigated. The bandgap energy showed no significant change at O/P = 3.0–3.4 but drastically decreased with the increase in the O/P from 3.6 to 4.0. In addition, the refractive index dispersion was analyzed based on the Lorentz model, and it was found that the decrease in the resonance frequency in the ultraviolet region with the increase in the O/P ratio resulted in an increase in the refractive index and dispersion. Analysis of the infrared absorption and Raman scattering spectra revealed that the phosphate chains were broken, and isolated Q0 units were generated with the increase in the O/P ratio from 3.6 to 4.0. Based on the structural change of the glass, the origin of the nonlinear dependence of the optical properties on the O/P ratio was discussed.

Solubility of Rare Earth Oxides in Fused Alkali and Alkaline Earth Halides

Melts based on mixtures of alkali and/or alkaline earth halides are considered as prospective media for electrowinning rare earth metals as well as for pyrochemical reprocessing spent nuclear fuels. Fluoride or mixed fluoride-chloride baths can be operated at high temperatures yielding molten rare earth metals (REMs) thus simplifying separation of the metal and salt. One of the problems in using fluoride melts is possible formation of fluorine at the anode. This can be avoided by adding a rare earth oxide to the melt both as the source of REM and oxide ions. The latter will be oxidized to oxygen producing carbon mono- or dioxide at the anode. The limiting factor for feeding the electrolysis bath with REM oxides is their solubility in the halide melt.The aim of the present study was determining the effect of temperature and melt composition on solubility of REM oxides in fused halides. The experiments were performed in CaCl2–CaF2 mixtures containing 20 or 75 mol. % CaF2; BaCl2–BaF2 mixtures containing 15 or 73 mol. % BaF2; equimolar CaF2–BaF2 mixture and NaCl–NaF eutectic mixture (34 mol. % NaF). Solubility of REM oxides was determined by the method of isothermal saturation. Time required for reaching the equilibrium between solid REM oxides and fused salts was determined in a preliminary set of experiments. To compare the behavior of 4f- and 5f-elements, solubility of uranium dioxide was also measured.The measurements were performed at the temperatures up to 1400 oC under argon atmosphere. The lower limit of the temperature range varied from 700 to 1100 oC depending on the melting temperatures of the salt mixtures used. Oxides of yttrium, lanthanum, cerium, praseodymium, neodymium and samarium were selected for the study. To assess a possible mutual influence of rare earth elements on solubility of their oxides in fused salts the solubility of a mixture of REM oxides was determined in a separate series of experiments and concentrations of individual REMs in the melt was determined.Solubility of REM oxides increased with increasing temperature and an example of effect of temperature on solubility of neodymium oxide in various melts is shown in Fig.Fig. Concentration of neodymium in alkali and alkaline halide based melts saturated with Nd2O3. Melt: CaCl2–CaF2 20 mol. % (1); CaCl2–CaF2 75 mol. % (2); BaCl2–BaF2 73 mol. % (3); BaCl2–BaF2 15 mol. % (4); CaF2–BaF2 50 mol. % (5; and NaCl–NaF 34 mol. % (6). Figure 1

Role of excitation wavelength and dopant concentration on white light tunability of dysprosium doped titania-fluorophosphate glasses

Abstract Dysprosium-doped fluorophosphate glasses (P2O5–CaF2–BaF2–TiO2-Dy2O3) have been prepared using melt-quenching technique and characterized their optical, structural, thermal and photoluminescence properties. Thermal stability (128 °C) of 0.5 mol% Dy2O3-doped glass has been estimated using Differential thermal analysis. Functional groups for 0.5 mol% Dy2O3-doped glass have been studied by Fourier Transform Infrared spectrum. Absorption spectra have been utilized for estimating the Judd-Ofelt (JO) parameters and allied properties. Several excitation wavelengths (350, 365, 387, 425, 452 and 472 nm) have been used for pumping the Dy3+ ions and analyzed for white luminescence. Intense emission has been observed for 0.5 and 1.5mol% of Dy2O3-doped glasses under 387 nm excitation. The 4F9/2 → 6H13/2 transition at 573 nm has unveiled a high stimulated emission cross-section (σSE) of 41.52 × 10−22 cm2 for 0.5 mol% Dy2O3-doped glass. CIE coordinates fall close to the white region in CIE diagram, and hence these glasses are suitable for cold white light emitting diode applications.

Solubility of Rare Earth Oxides in Fused Alkali and Alkaline Earth Halides

Solubility of rare earth oxides in mixtures of alkali or alkaline earth halides was determined by the method of isothermal saturation at the temperatures up to 1400oC. The melts studied included CaCl2–CaF2 (20 or 75 mol. % CaF2), BaCl2–BaF2 (15 or 73 mol. % BaF2), equimolar CaF2–BaF2 and eutectic NaCl–NaF mixtures. Melting points of the salt mixtures were determined by differential thermal analysis and effect of added rare earth oxide on the melting point was considered. Solubility of yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium oxides was determined. The effect of temperature, melt composition, and presence of a mixture of rare earth oxides on solubility was assessed.

Near infrared broadband and visible upconversion emissions of erbium ions in oxyfluoride glasses for optical amplifier applications

Optical and visible upconversion properties of erbium (Er3+)-doped oxyfluoro-titania-phosphate glasses (PCfBfTiEr) with the chemical composition of P2O5–CaF2–BaF2–TiO2–Er2O3 have been explored. An intense emission at 1.53 µm of Er3+-doped PCfBfTiEr1.0 glass was obtained upon excitation of 980 nm diode laser. In addition, green and red visible upconversion emissions were obtained upon the optical excitation of Er3+ ions doped PCfBfTiEr glasses at 980 nm diode laser. Upconversion emission intensities and population densities of respective levels were tuned with the variation of Er3+ ion concentration. Fluorescence decay curves of the 4I13/2 level of PCfBfTiEr glasses were obtained upon 980 nm laser excitation in the pulsed mode and revealed a mono-exponential behavior. The stimulated emission cross-section (σem), full width at half maximum (FWHM) and gain bandwidth product (σem × FWHM) were found to be 9.3 × 10−21 cm2, 95.61 nm and 889.2 cm−2 nm for PCfBfTiEr2.0 glass, respectively. These results recommend that the Er3+ ions doped PCfBfTiEr glasses may possibly be worthy for the laser and optical amplification applications at 1.53 µm.

Optical and spectroscopic properties of Ho3+-doped fluorophosphate glasses for visible lighting applications

Holmium (Ho3+)-doped fluorophosphate glasses (P2O5–BaF2–CaF2–TiO2–Ho2O3, PCfBfTiH) were fabricated by melt-quenching technique. The glass transition (548 °C) and crystallization (577 °C) temperatures and glass stability factor (161 °C) were obtained from DSC analysis. Judd-Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6) of PCfBfTiH15 glass were evaluated. Intense green (545 nm) emission was obtained for the 5S2 + 5F4 → 5I8 transition upon excitation of 451 nm. The stimulated emission cross-section (σem) of PCfBfTiH15 glass was found to be as high as 2.01 × 10−20 cm2. Decay curves of the 5S2 + 5F4 → 5I8 transition were analyzed by double exponential function. High lifetime of 11.29 μs for the 5S2 + 5F4 level was obtained. The CIE chromaticity coordinates for the emission spectra were professed that the green emission owing to the 5S2 + 5F4 → 5I8 transition may be useful for laser and display applications at around 545 nm.

Thermochemical properties and phase transitions of Ba–Sn alloys from thermal characterization and emf measurements

Thermodynamic properties of Ba–Sn alloys were determined for Ba mole fractions (xBa = 0.03–0.69) by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electromotive force (emf) measurements. Six intermetallic compounds (BaSn5, BaSn3, Ba3Sn5, BaSn, Ba5Sn3, and Ba2Sn) were identified by XRD and the phase transition temperatures were determined by DSC up to xBa = 0.50, which were used to delineate phase boundaries for constructing an experimentally-determined phase diagram. In addition, thermochemical solution properties were calculated by measuring emf values of Ba–Sn alloys using the following electrochemical cell: Ba(s) | CaF2–BaF2 | Ba(in Sn) over 713–1063 K, including activity and partial molar quantities of Gibbs energy, entropy, and enthalpy. The activity of Ba in Sn was as low as 1.5 × 10−11 at xBa = 0.03 and 923 K, indicating highly non-ideal solution behavior with a large excess partial molar Gibbs energy (−164 kJ mol−1). By integrating solution properties from emf measurements with the phase behavior by DSC and XRD, a reliable description of the Ba–Sn system was established.

Investigation of optical and spectroscopic properties of neodymium doped oxyfluoro-titania-phosphate glasses for laser applications

Nd3+-doped oxyfluoro-titania-phosphate glasses with a chemical combination, P2O5–CaF2–BaF2–TiO2–Nd2O3 (PCfBfTiNd), were synthesized by the regular melt-quenching method. These glass samples were investigated through optical absorption, emission, decay curves and spectroscopic ellipsometry analysis. Non-linear refractive index (n2) is evaluated using the Boling method and it was found to be as low as 3.68 × 10−16 cm2/W (1.36 × 10−13 esu). Emission spectra of Nd3+-doped glasses were obtained by laser excitation at a wavelength of 808 nm. Results were endorsed that the 0.5 mol% Nd3+-doped PCfBfTiNd05 glass could be a suitable gain media for the development of high-energy high-peak power lasers.

Theoretical Analysis of the Li, Ca, Ba∥F, WO4 System: Thermal Analysis of the Quaternary System LiF–BaF2–CaF2–BaWO4

The differentiation of the quaternary reciprocal system Li, Ca, Ba∥F, WO4 was performed based on graph theory using special software. Stable and metastable secant complexes of the system were found using a matrix of reciprocal pairs of salts. For the first time, by a set of physicochemical analysis methods (differential thermal, visual polythermal, and X-ray powder diffraction analyses), based on the method of thermal analysis of successive projections of the composition polytope, the quaternary system LiF–BaF2–CaF2–BaWO4, which is a stable complex of the quaternary reciprocal system Li, Ca, Ba∥F, WO4, was studied and the coordinates of invariant points were determined.

Spectroscopic properties and excited state dynamics of Sm3+ ions in zinc telluro-fluoroborate glasses

A new series of trivalent samarium doped B2O3–TeO2–ZnO–ZnF2–CaF2–BaF2 glasses were prepared and their spectroscopic behavior have been studied to understand the effect of Sm3+ ions concentration and to explore the local field effect on the symmetry around Sm3+ ions for the development of laser devices. Local structure and structural behavior are investigated through XRD, FTIR and Raman spectral measurements. The stretching vibrations of B‒O bond in BO3/BO4 units, Te–O stretching vibrations in TeO3/TeO4 units, and bending vibrations of B‒O‒B and Te‒O‒Te bonds were identified from FTIR and Raman spectral studies. Spectroscopic properties are investigated by recording optical absorption, excitation, luminescence and decay profiles. Judd-Ofelt (JO) theory has been implemented to get information about the local structure around Sm3+ ions in the chosen matrix using the experimental oscillator strength values obtained from the intensities of the absorption band transitions. Luminescence spectra of the Sm3+ ions doped present glasses were recorded by monitoring an excitation at 405 nm which exhibits 4G5/2→6HJ (J= 5/2, 7/2, 9/2 and 11/2) intra-4f transitions through an efficient energy transfer process. The luminescence quenching of Sm3+ ions emission were observed beyond 0.5 wt% of Sm3+ ion concentration which is mainly caused by the cross-relaxation process through various cross-relaxation channels and thus concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of the Sm3+ ions. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S= 6, which indicates that the nature of interaction takes place between Sm3+ ions for energy transfer through cross-relaxation is of dipole-dipole type.

Theoretical analysis of the system Li, K, Ca, Ba||F, WO4: Physicochemical properties of the system LiF–K2WO4–BaF2–CaF2–BaWO4

The differentiation of the quaternary reciprocal system Li, K, Ca, Ba||F, WO4 was performed based on the graph theory using special software. Stable and metastable complexes of the system were found using a matrix of reciprocal pairs of salts. For the first time, by a set of physicochemical analysis methods (differential thermal, visual polythermal, and X-ray powder diffraction analyses), based on the method of thermal analysis of successive projections of the composition polytope, the quaternary system LiF–K2WO4–CaF2–BaF2–BaWO4, which is a stable complex of the quaternary reciprocal system Li, K, Ca, Ba||F, WO4, was studied and the coordinates of invariant points were determined.

Ho3+-doped AlF3–TeO2-based glass fibers for 2.1 µm laser applications

Ho3+-doped AlF3–TeO2-based glass fibers based on AlF3–BaF2–CaF2–YF3–SrF2–MgF2–TeO2 glasses are fabricated by using a rod-in-tube method. The glass rod including a core and a thick cladding layer is prepared by using a suction method, where the thick cladding layer is used to protect the core from the effect of surface crystallization during the fiber drawing. By inserting the glass rod into a glass tube, the glass fibers with relatively low loss (~2.3 dB m−1 @ 1560 nm) are prepared. By using a 38 cm long Ho3+-doped AlF3–TeO2-based glass fiber as the gain medium and a 1965 nm fiber laser as the pump source, 2065 nm lasing is obtained for a threshold pump power of ~220 mW. With further increasing the pump power to ~325 mW, the unsaturated output power of the 2065 nm laser is about 82 mW and the corresponding slope efficiency is up to 68.8%. The effects of the gain fiber length on the lasing threshold, the slope efficiency, and the operating wavelength are also investigated. Our experimental results show that Ho3+-doped AlF3–TeO2-based glass fibers are promising gain media for 2.1 µm laser applications.

Enhanced 2.7 μm emission of Er3+-doped low hydroxyl fluoroaluminate–tellurite glass

New fluoroaluminate–tellurite glasses with high thermal stability were fabricated through introducing TeO2 into the fluoroaluminate glass (AlF3–YF3–CaF2–BaF2–SrF2–MgF2). 2.7μm emission properties were investigated through the measured absorption and emission spectra. For the first time it was found that the OH− absorption coefficient at 2.84μm was reduced to 1/15 for the fluoride system by introducing TeO2. X-ray diffraction showed that the sample without TeO2 composition showed some crystallization phases when the glass was reheated. However, the addition of TeO2 changed the crystallization mechanism and improved the glass forming ability of the fluoroaluminate glass. Enhanced 2.7μm emission was observed in the fluoroaluminate–tellurite glass under 980nm excitation and the calculated spontaneous transition probability (А), branching ratio (β) and emission cross section (σem) were larger than some reported values. These results indicate that this kind of fluoroaluminate–tellurite glass has potential applications as host material for 2.7μm lasers.

White light and multicolor emission tuning in triply doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate transparent glass-ceramics

Wide emission tunability was obtained in rare-earth ions doped NaPO3–YF3–BaF2–CaF2 glassy material by controlling the laser excitation and its crystallization rate.

Infrared to Visible Up‐Conversion Emission in Er3+/Yb3+ Codoped Fluoro–Phosphate Glass–Ceramics

Erbium Er3+ and ytterbium Yb3+ codoped fluoro‐phosphate glasses belonging to the system NaPO3–YF3–BaF2–CaF2 have been prepared by the classical melt‐quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV–visible and near‐infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X‐ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite‐type cubic crystals based during the devitrification process. Finally, infrared to visible up‐conversion emission upon excitation at 975 nm has been studied on the Er3+ and Yb3+ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up‐conversion emissions–about 150 times‐ has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare‐earth ions (REI) into the crystalline phase.

Effect of Fluoride Content on Friction and Wear Performance of Ni3Al Matrix High-Temperature Self-Lubricating Composites

The self-lubricating composites Ni3Al–BaF2–CaF2–Ag–Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The Ni3Al–6.2BaF2–3.8CaF2–12.5Ag–10Cr composite showed the best friction coefficients (0.29–0.38) and wear rates (4.2 × 10−5–2.19 × 10−4 mm3 N−1 m−1) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO4 on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property.

Nanotechnology studies of layered fluoride superionic conductors

A computer simulation by a molecular dynamics method at constant volume has been performed on a model material that is composed of accumulating two different fluoride conductors: ⋯BaF2–CaF2–BaF2–CaF2⋯. The average value of CaF2 and BaF2 for the lattice constant of the new layered material is prepared to hold its mechanical strength. The CaF2 region is compressed and the BaF2 region is stretched along the c axis (z axis) in the thermal equilibrium state. It is obtained that the diffusion coefficient and ionic conductivity of F − ions in the layered fluoride conductors increases with decreasing periods, more specifically with the number of interfaces. The layer depth dependence on transport coefficients approximately coincides with the experiment.

The Relationship Between 27 Al Quadrupolar Parameters and AlF 6 3– Octahedron Connectivity in Crystalline and Glassy Fluoroaluminates

27Al SATRAS and MQ-MAS spectra were recorded for eight crystalline compounds, from the CaF2–AlF3 and BaF2–AlF3 binary and BaF2–CaF2–AlF3 ternary systems, and four glass compositions with different CaF2/BaF2/AlF3 contents. For the crystalline phases, the reconstruction of the spectra leads to the precise determination of the NMR parameters. For the glassy phases, the 27Al SATRAS spectra have been reconstructed using quadrupolar parameter distributions. The main finding of this study is the dependence of the quadrupolar frequency on the type of AlF63– octahedron connectivity. For crystalline phases the experimental νQ values range between 75 kHz and 510 kHz for structures built up from isolated octahedra, and are between 560 kHz and 1250 kHz for structures built up from isolated chains of cis-connected octahedra, and are between 1530 kHz and 1580 kHz for structures built up from isolated chains of trans-connected octahedra. In the glassy phases the maximum of the quadrupolar frequency distribution shifts toward larger values and its width increases with increasing AlF3 content, and subsequently with the number of connected octahedra. The range of the νQ values seems to indicate that when the octahedra are connected, cis connections occur most frequently. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Localization of intrinsic defects in CaF2–BaF2 superlattices

We perform first-principles calculations for the formation energies of fluorine self-interstitials (Fi−) and fluorine vacancies (VF+) in CaF2–BaF2 superlattices and in the corresponding bulk compounds. In dislocation-free (strained-layer) superlattices, the calculations show that both the Fi− and the VF+ defects are energetically more stable in the CaF2 layers than in the BaF2 layers. If the misfit stress in the superlattices is released (by dislocations, for instance), our results indicate that charge transfer between layers becomes energetically favorable with Fi− in the CaF2 layers and VF+ in the BaF2 layers. This is consistent with recent experiments.

Phase diagram of the system LiF-NaF-CaF2-BaF2-BaF2-BaMoO4

The LiF–NaF–CaF2–BaF2–BaMoO4 system is studied by physicochemical analysis with the aim of developing a new phase-change thermal energy storage material. The compositions of the quinary eutectic (536°C) and peritectic (630°C) are determined. The enthalpy of fusion of the eutectic is 653 kJ/kg.