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Modulating the emissivity of yttria-stabilized zirconia (YSZ) ceramics in the 3–5 μm range through doping and structural adjustments is crucial for their application as high-temperature low-emissivity materials. This study examined YSZ composite ceramics with various levels of lanthanum fluoride (LaF 3) doping, sintered using a high-temperature solid-phase reaction method, to compare their infrared emissivity within the 3–5 μm range. A systematic investigation focused on the effects of the crystal structure and microporous structure evolution on the infrared emissivity of YSZ/LaF 3 composite ceramics. The results revealed that increasing the LaF 3 doping led to lattice expansion and an increase in oxygen vacancies within the YSZ. When the doping limit of La3+ ions is exceeded, La 2 Zr 2 O 7 is formed. At high doping levels, the formation of volatile ZrF 4 was identified as the primary cause of increased porosity of the composite ceramics. Consequently, the emissivity of the composite ceramics in the 3–5 μm range is minimized at a doping level of 3 mol%. For small amounts of doping, this represents the optimal balance between the lattice expansion and oxygen vacancies. However, at higher doping levels, the increased porosity becomes the dominant factor, reducing the emissivity of the composite ceramics. [ABSTRACT FROM AUTHOR]

Eu/Ag-co-doped transparent oxyfluoride glass-ceramics based on LaF 3 have been obtained by melt-quenching followed by structural analysis employing X-ray diffraction and transmission electron microscopy. Absorption spectra showed only Eu3+ ion transitions, irrespective of the presence of silver or the atmosphere used in the preparation. Excitation spectra obtained by collecting luminescence at 437 nm (Eu2+) and 612 nm (Eu3+) indicated the partial reduction of Eu3+ to Eu2+. As a consequence, by tuning the excitation wavelength, a variety of emission spectra are obtained, highlighting the coexistence of Eu2+ and Eu3+ ions, with the emission dominance of the type of ion dependent on the excitation wavelength. The presence of Ag and the atmosphere used during sample preparation affected the intensity of certain emissions, indicating the presence of oxidation-reduction reactions. Chromaticity diagrams illustrating the changes in colour coordinates corresponding to variations in the excitation wavelength showed a range of colours from red to blue, including purple-blue tones. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fluoride ion sensor electrodes that use polycrystalline LaF3 prepared by low‐temperature sintering can reduce sensor size and fabrication costs; however, decreasing the sintering temperature deteriorates sensor performance. Further, it is unclear why the performance of polycrystalline LaF3 prepared at low temperatures is inferior to that of the single‐crystal LaF3. Thus, in this study, we investigated factors that deteriorate sensor response under low sintering temperatures, such as solution penetration, fluorine conductivity, and ion exchange. To this end, LaF3 was prepared by changing the sintering temperature, and the electrical characteristics and sensor performance were evaluated and compared with those of the single‐crystal LaF3. The sensor performances of LaF3 sintered at 900 °C (−9.3 mV/dec) and 1000 °C (−5.8 mV/dec) were inferior to that of a single‐crystal LaF3 (−49.9 mV/dec). LaF3 prepared by sintering over 800 °C achieved fluorine removal and showed lower ion conductivity and ion exchange compared to that of the single‐crystal LaF3. LaF3 sintered at 700 °C did not show a sensor response because of solution penetration into the through‐pore. Our results confirmed that solution penetration, ion conductivity, and ion exchange influence the sensor performance of LaF3. Finally, we discussed approaches to achieve high sensor performance with LaF3 prepared by low‐temperature sintering. The proposed approaches are expected to contribute to expanding the utility of fluoride ion sensor electrodes with LaF3. [ABSTRACT FROM AUTHOR]

Nd3+-doped, LaF 3 -based, transparent oxyfluoride glass-ceramics (GCs) containing Ag nanoparticles (NPs) have been prepared by a melt-quenching method. Different Ag-containing precursors were employed, with AgNO 3 as the most suitable for obtaining Ag NPs segregated in the glassy matrix. Transmission electron microscopy and X-ray absorption spectroscopy determined the presence of Ag0 NPs, with higher concentrations in glass-ceramics produced in an inert atmosphere (N 2). The spectral features of emission and excitation spectra, in addition to the different lifetimes of the 4F 3/2 state in the co-doped samples with Ag NPs, demonstrate the incorporation of Nd3+ ions into the LaF 3 nanocrystals. The relative contribution to the emission from Nd3+ in the nanocrystals depends on the Ag concentration and atmosphere. The glass-ceramic co-doped with 0.2 wt% Ag, thermally treated in N 2 , exhibits the highest contribution of emissions attributable to Nd3+ ions in the crystalline phase. The crystalline fraction is similar to that of a Ag-free sample synthesized under analogous conditions. This increase of the luminescence is likely attributable to the enhancement of the local electric field in the LaF 3 nanocrystals due to the presence of Ag0 NPs. [ABSTRACT FROM AUTHOR]

This article details a method for preparing cermet matrix composites via Fast hot pressing (FHP) sintering technology and emphasizes their potential use in extremely high-temperature settings. The material primarily consists of NiCr alloy, Cr3C2, and LaF3. An in-depth investigation was conducted on the tribological properties of the specimen by conducting sliding tests against a Si3N4 ball at varying temperatures, including room temperature (RT), 400 °C, 600 °C, and 800 °C. Advanced techniques such as scanning electron microscopy, micro-XRD, and micro-Raman spectroscopy were employed to examine the friction surfaces formed under different frictional temperatures. The findings reveal a uniform composition and high density within the composites. It is noteworthy that as the LaF3 content increases, the hardness of the ceramic phase diminishes. Conversely, the hardness of the alloy phase augments with the addition of LaF3, provided that its content remains below 15 wt%. The composite material containing 15 wt% LaF3 demonstrates superior hardness values, with the ceramic phase reaching HV1412 and the alloy phase achieving HV384. Furthermore, the coefficient of friction of the composite material was evaluated. The coefficient of friction of the composite is between 0.74 and 0.4 and the wear rate is 4.46 × 10−6–5.72 × 10−5 mm3N−1m−1 from room temperature to 800 °C. The lubrication behavior at low temperature is mainly attributed to the lubricating effect of LaF3, and at high temperature it is due to the tribochemical reaction to form LaCrO3 with good lubricating properties, which plays a synergistic lubricating role with Cr2O3. [ABSTRACT FROM AUTHOR]

This study synthesized LaF3–LaOF:Yb3+/Ho3+via a solid-state reaction method and analyzed its optical properties and temperature sensitivity. Specifically, the crystalline structure of each sample—composed of LaOF (tetragonal) and LaF3 (hexagonal)—were analyzed under X-ray diffraction. In addition, their photoluminescence (PL) properties were analyzed, with peaks observed at 543, 654, and 755 nm. The highest PL intensity was observed at 543 nm for a molar ratio of La:Yb:Ho = 1:0.05:0.001. Furthermore, the temperature characteristics of each sample were analyzed to determine the absolute and relative sensitivities as 0.0232 K−1 and 0.357 %K−1, respectively. [ABSTRACT FROM AUTHOR]

This study synthesized LaF3–LaOF:Yb3+/Ho3+via a solid-state reaction method and analyzed its optical properties and temperature sensitivity. Specifically, the crystalline structure of each sample—composed of LaOF (tetragonal) and LaF3 (hexagonal)—were analyzed under X-ray diffraction. In addition, their photoluminescence (PL) properties were analyzed, with peaks observed at 543, 654, and 755 nm. The highest PL intensity was observed at 543 nm for a molar ratio of La:Yb:Ho = 1:0.05:0.001. Furthermore, the temperature characteristics of each sample were analyzed to determine the absolute and relative sensitivities as 0.0232 K−1 and 0.357 %K−1, respectively. [ABSTRACT FROM AUTHOR]

This article details a method for preparing cermet matrix composites via Fast hot pressing (FHP) sintering technology and emphasizes their potential use in extremely high-temperature settings. The material primarily consists of NiCr alloy, Cr3C2, and LaF3. An in-depth investigation was conducted on the tribological properties of the specimen by conducting sliding tests against a Si3N4 ball at varying temperatures, including room temperature (RT), 400 °C, 600 °C, and 800 °C. Advanced techniques such as scanning electron microscopy, micro-XRD, and micro-Raman spectroscopy were employed to examine the friction surfaces formed under different frictional temperatures. The findings reveal a uniform composition and high density within the composites. It is noteworthy that as the LaF3 content increases, the hardness of the ceramic phase diminishes. Conversely, the hardness of the alloy phase augments with the addition of LaF3, provided that its content remains below 15 wt%. The composite material containing 15 wt% LaF3 demonstrates superior hardness values, with the ceramic phase reaching HV1412 and the alloy phase achieving HV384. Furthermore, the coefficient of friction of the composite material was evaluated. The coefficient of friction of the composite is between 0.74 and 0.4 and the wear rate is 4.46 × 10−6–5.72 × 10−5 mm3N−1m−1 from room temperature to 800 °C. The lubrication behavior at low temperature is mainly attributed to the lubricating effect of LaF3, and at high temperature it is due to the tribochemical reaction to form LaCrO3 with good lubricating properties, which plays a synergistic lubricating role with Cr2O3.

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an important functional material, lanthanum fluoride (denoted as LaF3) shows promising application in infrared thermometry, infrared thermography and fluoride glass optical fiber, etc. Although great process has been obtained in preparing rare earth fluorides such as GdF3, YF3, and NdF3, the thermodynamic process and synthesis of LaF3 remain a challenge. Herein, the thermodynamic process is explored by theoretical calculation and cxs Δ r H <0, Δ r G <0, K p >109, indicating that the whole fluorination reaction is an exothermic reaction and can be fully carried out. Moreover, we now report an optimum fluorination process of LaF3. By exploring the effects of reaction temperature, holding time, material layer thickness and HF gas flow on fluorination rate k, the reliability of theoretical calculation has been verified, the best fluorination parameters have been obtained and the fluorination rate can reach more than 97%. This work may shed some light on the large-scale industrial production of high-grade LaF3, and promote its applications in infrared optical field, nuclear medicine and high-energy physics. [ABSTRACT FROM AUTHOR]

Lanthanum fluoride (LaF3) thin films were deposited on the Ge substrate using the molybdenum boat evaporation method. The effect of films' oxygen impurity on the infrared optical properties has been investigated for the first time in this report. With the increase in oxygen content in the films, the F content decreases, and the O/F ratio decreases from 0.160 to 0.055. XRD patterns reveal that the presence of O impurity destroys the crystal structure integrity of the LaF3 films and leads to the intensification of infrared absorption. The average transmittance decreases from 58.1% to 52.2%, and the peak transmittance decreases from 59.9% to 54.5%. Additionally, the refractive index and extinction coefficient of LaF3 films with different oxygen content are obtained by fitting the transmittance test data. The results show that the refractive index and extinction coefficient of the films in 8–12 μm increase with the increase in oxygen content, the average refractive index increases from 1.339 to 1.478, and the extinction coefficient increases from 0.001 to 0.030. In this paper, the influence of oxygen impurity in the LaF3 film on its infrared optical properties is revealed, which lays a theoretical foundation for the development of high-performance LaF3 infrared antireflective film. [ABSTRACT FROM AUTHOR]

Controllable growth of nanocrystals (NCs) in optical glasses is essential to impart photonic functions for demanded applications. Here, Ce3+-doped KLaF 4 and LaF 3 fluoride NCs are controllably precipitated in a fluorosilicate glass via adjusting the duration and temperature of thermal treatment. The presence of phase separation in the precursor glass (PG) is derived from molecular dynamics (MD) simulations, and serves as the driving factor for the crystallization of fluoride NCs. The phase separation of PG, NCs distribution, microscopic morphology and particle size of NCs precipitated in the nano-glass composites (nano-GCs) are investigated by analytical transmission electron microscopy (TEM). Structural and spectroscopic characterizations confirm the influence of the thermal treatment on the crystalline species in the nano-GCs. The developed nano-GCs exhibit intense X-ray excited luminescence with an excellent linearity with the X-ray dosage and a good thermal stability, making them suitable for radiation detection and medical imaging applications. [ABSTRACT FROM AUTHOR]

LaF3:Eu nanophosphors were prepared by a traditional hydrothermal method with citric acid as a reducing agent. X‐ray diffraction, scanning electronic microscopy, and luminescence spectroscopy were used to study the nanophosphors. The formation of three different luminescence centers of Eu2+ and two different luminescence centers of Eu3+ is attributed to the existence of abundant surface defects in this nanophosphor. Eu3+ is effectively excited by energy transfer from Eu2+ to Eu3+. The excitation wavelength of Eu3+ covers a broad spectral range from 250 to 480 nm. The nanophosphor shows a tunable luminescence color varying from blue to white and then to red, which is explained from three aspects of Eu concentration, energy transfer, and concentration quenching. Utilizing the surface defect of nanoparticles to control the reduction of Eu3+ is considered a promising strategy for exploring Eu2+ and Eu3+ codoped phosphor suitable for the lighting and display application. [ABSTRACT FROM AUTHOR]

In this study, emissions between 350 nm and 2.8 μm are produced from molten-salt-synthesized LaF3:Yb3+,Er3+ (LFYE) nanocrystals (NCs) under 980 nm excitation. In fact, such wide spectral emissions from a single phosphor would be highly favorable in lighting applications ranging from light-emitting diodes, optical fibers, and telecommunications. Upconversion luminescence (UCL) spectra show intense red emission compared to the green band below 6 mW, wherein a strong green emission is achieved compared to a red emission when the laser power is increased beyond 85 mW. To further enhance their UCL and downconversion luminescence (DCL), the LFYE NCs are annealed at 400 °C for 30, 60, 90, and 120 min. Their UCL and DCL intensities are improved with up to 90 min of annealing but drastically reduced after annealing for 120 min. The latter is caused by both phase transition and shape changes, that is, from the cubic LFYE NCs to tetragonal LaOF:Yb3+,Er3+ (LOFYE) NCs with a square pyramidal shape. Density functional theory calculations show that the LOFYE NCs are more thermodynamically favorable to form due to their lower defect formation energy than the LFYE NCs. Moreover, LaF3 is dynamically more unstable in comparison to LaOF, as indicated by a greater number of imaginary modes for LaF3 in the phonon dispersion plot. Interestingly, the highest phonon energy for LaF3 is found to be 439 cm–1 while that of LaOF is 527 cm–1, which is expected to play a role in the different emission behaviors between LaF3 and LaOF. Our work shows exemplary potential of the LFYE NCs with near-ultraviolet to mid-infrared emissions as UCL and DCL for laser power-induced color tunability for a wide range of applications. [ABSTRACT FROM AUTHOR]

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF3 NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8–15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission 4S3/2 → 4I/15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications. [ABSTRACT FROM AUTHOR]

Judd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr3+ activated materials, the procedure is additionally complicated due to strong interaction of low‐lying Pr3+ 4f5d energy levels with the 4f levels. Here, the straightforward JO parametrization method that uses the emission spectrum and the excited state lifetime of the Pr3+ 3P0 level which does not require any fitting procedure are shown. In addition, the theory and software for calculations of JO parameters from Pr3+ emission are explained. The method requirements are low‐temperature photoluminescence measurements of Pr3+ introduced in low phonon energy hosts with a relatively high lying 4f5d energy level. The method is demonstrated on emissions of YF3:Pr3+ and LaF3:Pr3+ powders. [ABSTRACT FROM AUTHOR]

Judd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr3+ activated materials, the procedure is additionally complicated due to strong interaction of low‐lying Pr3+ 4f5d energy levels with the 4f levels. Here, the straightforward JO parametrization method that uses the emission spectrum and the excited state lifetime of the Pr3+ 3P0 level which does not require any fitting procedure are shown. In addition, the theory and software for calculations of JO parameters from Pr3+ emission are explained. The method requirements are low‐temperature photoluminescence measurements of Pr3+ introduced in low phonon energy hosts with a relatively high lying 4f5d energy level. The method is demonstrated on emissions of YF3:Pr3+ and LaF3:Pr3+ powders. [ABSTRACT FROM AUTHOR]

MoS 2 -based films are the most widely used solid lubrication materials in the space environment. However, the environmental sensitivity of MoS 2 determines its low lifetime in low-orbit space environments rich in atomic oxygen (AO). To solve this problem, we optimize the film structure by doping with LaF 3 , which has a hexagonal structure and grain refinement properties. The TEM-FIB cross-section visualization illustrates that the LaF 3 doping can further reduce the voids in the film and improve densification, which improves the AO-resistance of the film and maintains excellent tribological properties with a low friction coefficient of 0.017 and a friction life of more than 1.5 × 106 laps after high-flux AO irradiation. [ABSTRACT FROM AUTHOR]

The local structure around the dopant atom in Nd(8 mol%):LaF3 single‐crystal scintillator is analyzed by X‐ray fluorescence holography experiments in combination with a sparse modeling algorithm. The average local environment of Nd is reconstructed up to large distances of about 12 Å and confirms a substitution of La atoms with Nd with only small crystal lattice distortions. The experimental findings are substantiated by comparison with reference data from La holograms and with computationally generated holograms based on a model structure of the dopant site. [ABSTRACT FROM AUTHOR]

Slow highly charged ions (HCI) were utilized successfully for the formation of various nanostructures in the surfaces of different materials. The creation mechanism of HCI-induced nanostructures was intensively studied in alkali- and alkaline-earth fluorides. Here, we are investigating another type of fluorine-containing ionic crystals of different crystalline and electronic structure, namely lanthanum fluoride, LaF 3. The single crystals were irradiated with slow (eV-keV) highly charged xenon ions from an Electron Beam Ion Trap. After irradiation, the crystals surfaces were investigated by scanning force microscopy. The measured topographic images show nanohillocks emerging from the surface. These nanostructures were observed only after exceeding a well-defined threshold in the potential energy. The role of ion parameters for nanohillocks formation as well as a comparison with results for swift heavy ion irradiations of LaF 3 single crystals are presented. Furthermore, the similarities and differences between LaF 3 and other ionic fluoride crystals, in the creation of surface nanostructures, are discussed. [ABSTRACT FROM AUTHOR]

Mixed‐valence Eu‐doped transparent oxyfluoride glass‐ceramics containing cubic LaF3 nanocrystals were fabricated by traditional melt‐quenching technique and consequent annealing processes. Their structural and luminescent properties were systemically investigated by X‐ray diffraction (XRD), transmission electron microscopy, absorption, excitation, emission spectra, and fluorescence lifetime measurements. Analyses of XRD patterns prove that the new precipitated nanocrystals disperse in glass‐ceramics crystallize in cubic LaF3. The spectroscopic investigations show that Eu2+ ions have been incorporated into the LaF3 nanocrystals preferentially, while Eu3+ ions still remain in the glass phase after crystallization. Based on the spectral results, a new parameter Rchange=RGC-RPG/RGC was defined to describe the changes of the environments of Eu3+ before and after crystallization more straightforwardly and more sensitively, where RPG and RGC represent the integrated intensity radio of 5D0 → 7F2 to 5D0 → 7F1 emissions of Eu3+ in PG and GC samples, respectively. Our investigation will not only enrich the understanding of fluoride nanocrystals‐based oxyfluoride glass‐ceramics, but also the distribution and luminescence behaviors of Eu3+ ions in them. [ABSTRACT FROM AUTHOR]

Zirconium Boride is widely used as thermal protection materials. However, the characteristics of poor oxidation resistance of ZrB 2 at high temperatures limits its applications. In order to improve the anti-oxidation performance of ZrB 2 , a novel method of doping LaF 3 is adopted in present study. In the synthesis process of ZrB 2 via carbothermal reduction method, LaF 3 was introduced to the initial materials. Motivated by the slightly higher formation temperature of ZrB 2 than the melting point of LaF 3 , a liquid glass phase composed of F and La was deposited on the surface of ZrB 2 , which naturally brought in oxygen starvation and contributed to improved oxidation resistance performance. The crystal lattice parameters and the anti-oxidation ability of ZrB 2 are closely dependent on the added LaF 3 content, which can ascribe to La3+/Zr2+ substitution and the amount of glass phase on the surface of ZrB 2. [ABSTRACT FROM AUTHOR]

Electrochemical studies of LaF 3 in molten FLiNaK salt were performed on inert working electrodes. An additional reduction reaction prior to the decomposition of FLiNaK melt was observed when LaF 3 was dissolved in and the reduction product was later recognized as lanthanum metal by SEM analysis. This phenomenon is very surprising and interesting considering the standard reduction potential of La (III) is more cathodic than that of K (I) and Na (I). The present study corrected the previous study [ 1 ] and will provide a new insight on the electrochemical and thermodynamic investigation of other lanthanides in molten FLiNaK salt. [ABSTRACT FROM AUTHOR]

Herein, we successfully synthesized a series of LaF3:Yb3+/Er3+/Ho3+/Tm3+ upconversion nanoparticles (UCNPs) and LaF3:Yb3+0.20, Er3+0.02@LaF3:Yb3+0.20 core/shell UCNPs by modifying the amount of NaOH and the reaction time. Hexagonal LaF3 nanocrystals with uniform particle sizes and bright UC emissions were obtained. The crystal structures of the lanthanide-doped LaF3 UCNPs were investigated using wide-angle X-ray diffraction. The morphologies and particle sizes of the nanocrystals were determined using transmission electron microscopy. The photoluminescence (PL) spectra of the LaF3 nanocrystals could be tuned by altering the doping ratio of Er3+, Ho3+, and Tm3+. In addition, the PL intensities increased after coating the UCNP cores with an active shell. The fluorescence intensities of the UCNPs synthesized via a one-hour reaction with the addition of 2.5 or 5 mmol NaOH increased by up to 17 times compared with the sample prepared without the addition of NaOH. By modifying the doping ratio of Yb/Tm, UV-emissive LaF3 nanocrystals were obtained. After surface modification by ligand exchange, the hydrophobic LaF3:Yb3+0.20, Er3+0.02@LaF3:Yb3+0.20 core/shell UCNPs became water-dispersible. These colloid UCNPs could be utilized as a fluorescent probe for the detection of Hg2+ ions under 980 nm near-infrared irradiation.

The equivalent parameters function in Macleod software can be used to calculate the equivalent admittance and phase thickness of multilayers, even when the material is both absorbing and dispersive, and the incidence angle is non-zero. We utilized this software to design first-order 121.6 nm minus filters based on a lanthanum trifluoride (LaF3)/magnesium fluoride (MgF2) multilayer; a Gaussian-type target curve was also introduced into the design. Minus filters with bandwidths of 10 and 5 nm were obtained and had good visible light suppression and low side-lobe ripples. This designed filter will be fabricated for use in a Lyman-alpha coronagraph and imager installed in the Lyman-Alpha Solar Telescope, which will be launched by China in 2021. [ABSTRACT FROM AUTHOR]

In the far-ultraviolet (UV) region, optical materials are dispersive and absorbing. The previous successful design method utilized in the visible band should be re-examined. We report on the design and fabrication of a far-UV reflective broadband filter based on dielectric materials lanthanum fluoride (LaF3) and magnesium fluoride (MgF2). Extended bandwidth technology is utilized in designing this filter. The obtained filter has a high reflectance in the working wavelength range of 140–180 nm, meanwhile, with good suppression in shorter and longer wavelength regions. In 2016, this filter was employed in a wide-angle aurora imager (WAAI) installed in the Feng Yun III satellite that will be launched in China. [ABSTRACT FROM AUTHOR]

We report a one-pot solvothermal synthesis of sub-10 nm, dominant ultraviolet (UV) emissive upconverting nanocrystals (UCNCs), based on sodium-codoped LaF3 and BaLaF5 (0.5%Tm; 20%Yb) and their corresponding core@shell derivatives. Elemental analysis shows a Na-codopant in these crystal systems of ~20% the total cation content; X-ray diffraction (XRD) data indicate a shift in unit cell dimensions consistent with these small codopant ions. Similarly, X-ray photoelectron spectroscopic (XPS) analysis reveals primarily substitution of Na+ for La3+ ions (97% of total Na+ codopant) in the crystal system, and interstitial Na+ (3% of detected Na+) and La3+ (3% of detected La3+) present in (Na)LaF3 and only direct substitution of Na+ for Ba2+ in Ba(Na)LaF5. In each case, XPS analysis of La 3d lines show a decrease in binding energy (0.08–0.25 eV) indicating a reduction in local crystal field symmetry surrounding rare earth (R.E.3+) ions, permitting otherwise disallowed R.E. UC transitions to be enhanced. Studies that examine the impact of laser excitation power upon luminescence intensity were conducted over 2.5–100 W/cm2 range to elucidate UC mechanisms that populate dominant UV emitting states. Low power saturation of Tm3+ 3F3 and 3H4 states was observed and noted as a key initial condition for effective population of the 1D2 and 1I6 UV emitting states, via Tm-Tm cross-relaxation.

Over the past years, ceramic fluorine ion conductors with high ionic conductivity have stepped into the limelight of materials research, as they may act as solid-state electrolytes in fluorine-ion batteries (FIBs). A factor of utmost importance, which has been left aside so far, is the electrochemical stability of these conductors with respect to both the voltage window and the active materials used. The compatibility with different current collector materials is important as well. In the course of this study, tysonite-type La 0.9 Ba 0.1 F 2.9 , which is one of the most important electrolyte in first-generation FIBs, was chosen as model substance to study its electrochemical stability against a series of metal electrodes viz. Pt, Au, Ni, Cu and Ag. To test anodic or cathodic degradation processes we carried out cyclic voltammetry (CV) measurements using a two-electrode set-up. We covered a voltage window ranging from −1 to 4 V, which is typical for FIBs, and investigated the change of the response of the CVs as a function of scan rate (2 mV/s to 0.1 V/s). It turned out that Cu is unstable in combination with La 0.9 Ba 0.1 F 2.9 , even before voltage was applied. The cells with Au and Pt electrodes show reactions during the CV scans; in the case of Au the irreversible changes seen in CV are accompanied by a change in color of the electrode as investigated by light microscopy. Ag and Ni electrodes seem to suffer from contact issues which, most likely, also originate from side reactions with the electrode material. The experiments show that the choice of current collectors in future FIBs will become an important topic if we are to develop long-lasting FIBs. Most likely, protecting layers between the composite electrode material and the metal current collector have to be developed to prevent any interdiffusion or electrochemical degradation processes.

• The Pr:LaF 3 crystals with different doping concentrations were grown by the Bridgman method with the dimension is about Φ20 mm × 30 mm. • The effects of Pr3+ doping concentration on the LaF 3 crystal optical properties were expounded for the first time. • The continuous-wave (cw) deep red laser were obtained with different doping concentrations of Pr:LaF 3 crystals pumped by an blue laser diode for the first time. The crystal compositions, fluorescence lifetimes, polarized absorption and emission spectra, and laser performance were measured with different doping concentrations of Pr:LaF 3 crystals. Moreover, the effects of Pr3+ doping concentration on LaF 3 crystal optical properties were expounded for the first time. The study found that high doping concentration is easy to cause cross-relaxation, which in turn leads to a decrease in the lifetime of the laser upper energy level. And then affects the output efficiency of the visible laser. The laser experiment results confirm that the maximum output power of 176 mW was obtained with Pr:LaF 3 crystal of 0.5 at.% doping concentration, which is higher than output power (71.3 mW) of 1 at.% doping concentration crystal. As we all know, this is the first report about continuous-wave (cw) laser operation with Pr:LaF 3 crystal pumped by an blue laser diode. [ABSTRACT FROM AUTHOR]

The magnetic properties of LaF 3 :1%Pr3+ fluoride nanoparticles were studied in comparison with bulk LaF 3 :1%Pr3+ crystal and microcrystalline powder using EPR and magnetization measurements complemented by XRD and TEM methods. LaF 3 :1%Pr3+ fluoride nanoparticles were synthesized by co-precipitation method and had two morphotypes: nanospheres and nanoplates. Microcrystalline powder was obtained by grinding a bulk LaF 3 :Pr3+ crystal using a pestle and a mortar. We have found the room temperature ferromagnetic-like response in magnetization measurements for nano- and microcrystalline powders whereas no such response was observed for the bulk crystal. We supposed that surface defects play a key role in the observed magnetization dependences on the magnetic field. • LaF 3 :1%Pr3+ nanocrystals were synthesized via the co-precipitation. • LaF 3 :1%Pr3+ microcrystals were prepared by grinding of the bulk crystals. • Magnetization curves show a weak "ferromagnetism" in powder samples. • The EPR spectra of LaF 3 :1%Pr3+ nano- and micro-crystals are studied. • The possible origin of the observed room temperature "ferromagnetism" is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Neutron imaging devices employing a scintillator can be used in various fields, and eutectic crystals can be suitable for the imaging with a fine position resolution of a few hundred micrometers. Since LiF and LaF3 have different refractive indexes of 1.41 and 1.64 at 300nm, respectively, the eutectic crystal is expected to behave as a scintillator with light guiding properties. Thus, the optical properties of Ce-doped LiF/LaF3 eutectic crystal grown by micro-pulling down method were investigated. The light output of LiF/Ce:LaF3 eutectic crystal was relatively small. The emission peaks at 300nm originating from Ce3+ of 5d–4f transition were observed under excitation by UV photons and 5.5MeV alpha rays. Moreover, the photo-luminescence decay time of Ce-doped LiF/LaF3 eutectic crystal was estimated to be 17±1ns. [Copyright &y& Elsevier]

Highlights: [•] The obtained lattice constants of LaF3 are in good agreement with the experimental data. [•] The pressure dependences of elastic constants of LaF3 are investigated for the first time. [•] Calculated band-gap of LaF3 is better than other calculations when compared with experiment. [•] The thermodynamic properties of LaF3 are calculated through quasi-harmonic approximation (QHA) model for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Energy transfer phenomena can play an important role in the development of luminescent materials, and hosts co-doped with Ce3+ and Tb3+ ions continue to be actively studied. Several recent reports on Ce, Tb co-doped phosphors suggest different mechanisms for the energy transfer from Ce3+ to Tb3+ ions and further study is required to reach consensus on the mechanism or to understand why different mechanisms dominate in different hosts. A more direct method of analysis is proposed to distinguish between the different types of multipole energy transfer mechanisms. When applied to Ce, Tb co-doped LaF3, the experimental data shows a poor match to any of these models but is consistent with energy transfer through the exchange mechanism. The decay curves of Ce emission in Ce, Tb co-doped LaF3 were also studied to obtain further insight on the energy transfer mechanism. Although the decrease in lifetime with increasing Tb concentration shows that energy transfer occurs through a non-radiative mechanism, the form of the decay curves does not correspond to what is expected for energy transfer via multipole interactions. [Copyright &y& Elsevier]

We report a one-pot solvothermal synthesis of sub-10 nm, dominant ultraviolet (UV) emissive upconverting nanocrystals (UCNCs), based on sodium-codoped LaF3 and BaLaF5 (0.5%Tm; 20%Yb) and their corresponding core@shell derivatives. Elemental analysis shows a Na-codopant in these crystal systems of ~20% the total cation content; X-ray diffraction (XRD) data indicate a shift in unit cell dimensions consistent with these small codopant ions. Similarly, X-ray photoelectron spectroscopic (XPS) analysis reveals primarily substitution of Na+ for La3+ ions (97% of total Na++ codopant) in the crystal system, and interstitial Na++ (3% of detected Na+) and La3+ (3% of detected La3+) present in (Na)LaF3 and only direct substitution of Na+ for Ba2+ in Ba(Na)LaF5. In each case, XPS analysis of La 3d lines show a decrease in binding energy (0.08-0.25 eV) indicating a reduction in local crystal field symmetry surrounding rare earth (R.E.3+) ions, permitting otherwise disallowed R.E. UC transitions to be enhanced. Studies that examine the impact of laser excitation power upon luminescence intensity were conducted over 2.5-100 W/cm² range to elucidate UC mechanisms that populate dominant UV emitting states. Low power saturation of Tm3+ ³F3 and ³H4 states was observed and noted as a key initial condition for effective population of the ¹D2 and ¹I6 UV emitting states, via Tm-Tm cross-relaxation. [ABSTRACT FROM AUTHOR]