Lanthanum Fluoride Research Articles

Microstructural and ionic transport studies of hydrothermally synthesized lanthanum fluoride nanoparticles

This article presents the structural and transport characteristics of hydrothermally synthesized LaF3 nanoparticles with an average crystallite size of 35nm. The phase formation of the material is confirmed by both X-ray diffraction and transmission electron microscopy techniques. In addition, phase purity of the LaF3 nanoparticles is corroborated by micro-Raman spectroscopy studies. The complex impedance plots at different temperatures reveal that the conductivity is predominantly due to the intrinsic bulk grains and the conductivity relaxation is non-Debye in nature. The frequency variation of conductivity exhibits dispersion at higher frequencies that can be explained with the frame work of Almond-West formalism. The conduction process is controlled by the mobility of the charge carriers and the charge of transport of mobile fluoride ions occur through hopping mechanism. The scaling behavior of both frequency dependence of conductivity and complex impedance plots at different temperatures confirm that the relaxation mechanism of the mobile fluoride ions is independent of temperature.

Synthesis of fluorozirconate ZBNL glass with partial or complete substitution of europium difluoride for barium (lanthanum) fluorides

The vitrification in two sets of fluorozirconate glass 53.5ZrF4 · 20NaF · 20BaF2 · (6.5 − x)LaF3 · xEuF2 (0 ≤ x ≤ 6.5 mol %) (I) and 53.5ZrF4 · 20NaF · (20 − x)BaF2 · 6.5LaF3 · xEuF2 (0 ≤ x ≤ 20 mol %) (II) has been studied. It has been determined that, in set I, at full or partial replacement of lanthanum fluoride by europium difluoride (1–6.5 mol %), colorless transparent glass is formed. In the samples of set II, at the substitution of BaF2 in order to obtain stable glass under analogous conditions, the initial batch should not contain more than 7.0 mol % EuF2. The methods of differential-thermal and X-ray phase analyses and IR and electron spectroscopy were used to study the properties and phase composition of the obtained glass and vitrocrystalline materials. Using the Grubi criterion, the optimal, with respect to crystallization, EuF2 content has been deter-mined in the glass of both systems. In the devitrified glass of series II, the low-temperature modification of compound EuZrF6 is formed, in addition to sodium, barium, and lanthanum fluorozirconates. For the vitro-crystalline samples, the absorption bands of Eu-F bonds are observed in infrared spectra, in addition to the broad band (∼500 cm−1), which is intrinsic for all fluorozirconate glass. The electron diffuse reflection spectra confirm the presence of both double and triple-charged europium ions in glass.

A probe into compositional and structural dependence of optical properties of lanthanum fluoride films prepared by resistive heating

The paper describes investigations into the correlation between the optical properties and the composition, structure and morphology of lanthanum fluoride films deposited at 373–473K substrate temperatures by resistive heating of lanthanum fluoride powders. The composition of the films that includes depth profiling of fluorine has been determined non-destructively by ion beam analysis while their structure and morphology have been investigated by glancing incidence X-ray diffraction and atomic force microscopy respectively. The films are polycrystalline, exist in hexagonal phase and display substrate temperature dependent texturing. The substrate temperature has an important influence on composition as well. The films deposited at 373K or 398K substrate temperatures are deficient in fluorine but tend to acquire stoichiometric composition at 473K. Possessing granular (∼100nm) morphology, the films, in general, are UV transparent but their optical loss increases with texturing. Carbon and oxygen, present as impurities, lower the density and consequently the refractive index (1.47) of the films. Annealing in vacuum at 573K brings about deterioration in the optical properties of the films which are related mainly to morphological changes and thermal stress.

Influence of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/porous-silicon structure prepared by chemical bath deposition technique

Effect of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/PS heterojunction has been investigated in this report. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique LaF3 produced as LaCl3 are made to react with hydrofluoric acid on the porous silicon (PS) substrate. This enables direct deposition of LaF3 on the pore walls of the PS leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by energy dispersive of X-ray analysis. The diode ideality factor increases with LaCl3 concentration and decreases with annealing temperature. Therefore, by changing the LaCl3 concentration and annealing temperature quality of the LaF3 layer on PS can be optimized. It was also seen that the Ag/LaF3/PS/Si/Ag structure showed the formation of Schottky diode with a threshold voltage of about 5.5 V. From the experimental results it can be concluded that lanthanum fluorides can be deposited into the pores as well as on the top of PS by the CBD technique, which provides the required passivation for PS. This passivation can enable the PS to be considered as an important material for photonics.

X-Ray-Induced Nanoparticle-Based Photodynamic Therapy of Cancer

In this study, Ce(3+)-doped lanthanum(III) fluoride (LaF3:Ce(3+)) nanoparticles were synthesized by a wet-chemistry method in dimethyl sulfoxide (DMSO) and their application as an intracellular light source for photodynamic activation was demonstrated. The LaF3:Ce(3+)/DMSO nanoparticles have a strong green emission with a peak at approximately 520 nm, which is effectively overlapped with the absorption of protoporphyrin IX (PPIX). The nanoparticles were encapsulated into poly(D,L-lactide-co-glycolide (PLGA) microspheres along with PPIX. Upon irradiation with x-rays (90 kV), energy transfer from the LaF3:Ce(3+)/DMSO nanoparticles to PPIX occurs and singlet oxygen is generated for cancer cell damage. The LaF3:Ce(3+)/DMSO/PLGA or LaF3:Ce(3+)/DMSO/PPIX/PLGA microspheres alone caused only sublethal cytotoxicity to the cancer cells. Upon x-ray irradiation, the LaF3:Ce(3+)/DMSO/PPIX/PLGA microspheres induced oxidative stress, mitochondrial damage and DNA fragmentation on prostate cancer cells (PC3). The results indicate that x-rays can activate LaF3:Ce(3+) and PPIX nanocomposites, which can be a novel method for cancer destruction.

Preparation and tribological properties of fluorosilane surface-modified lanthanum trifluoride nanoparticles as additive of fluoro silicone oil

Abstract LaF 3 nanoparticles surface-modified with fluorosilane were synthesized by surface modification technology. The size, morphology and phase structure of as-prepared surface-modified LaF 3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of surface-modified LaF 3 nanoparticles as additive of fluoro silicone oil were evaluated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined with a scanning electron microscope and an X-ray photoelectron spectroscope. Results show that 3-(heptafluoroisopropoxy)propyltriethoxysilane as the modifier is able to improve the dispersibility of LaF 3 nanoparticles in fluoro silicone oil. Moreover, when the optimum concentration, 0.08 wt.% of fluorosilane surface-modified LaF 3 is added into fluoro silicone oil, as-synthesized fluorosilane surface-modified LaF 3 nanoparticles exhibit excellent anti-wear as additive in fluoro silicone oil. The wear scar diameter under the optimum concentration is always smaller than that under the lubrication of fluoro silicone oil alone. Especially, when the load is 500 N, 600 N and 700 N, the wear scar diameter is reduced by 17%, 43% and 42%, respectively. In addition, during the friction process, LaF 3 nanoparticles are deposited on the rubbed steel surface to form LaF 3 deposition layer which functions jointly with the boundary lubricating film thereby resulting in improved tribological properties.

Luminescence properties of LaF3:Ce nanoparticles encapsulated by oleic acid

Cerium ions doped lanthanum fluoride (LaF3:Ce) nanopowder as well as LaF3:Ce nanopowder whose surfaces was modified by oleic acid (OA) were synthesized by using an in-situ hydrothermal process under the various doping concentrations. Based on the XRD spectra and TEM images, it was confirmed that the crystalline structured hexagonal LaF3:Ce nanopowder was synthesized. Oleic acid was efficient for conversion of the water dispersible LaF3:Ce nanoparticles to hydrophobic ones. Surface modification was verified by FTIR absorption spectrum as well as TEM images, showing no agglomeration between 5 and 10nm scaled particles. Photoluminescence based on 5d⟶4f electronic transition of cerium ions excited at λex ∼256nm for both neat and OA encapsulated LaF3:Ce nanoparticles decreases as the cerium concentration increases, while the quantum yields of OA encapsulated nanoparticles were much lower than the neat particles due to low photon transmittance of OA at the range longer than ∼350nm.

Using Lanthanum Fluoride Fine Particles as Stationary Phase for Thin-Layer Chromatography/Fourier Transform Infrared Spectroscopy Analysis

While in situ TLC/FTIR technique has tremendous potential in the analysis of complex mixtures, the conventional stationary phase, such as silica gel, used for TLC/FTIR analysis, has strong absorption in IR region and thus brings about severe interference in the obtained FTIR spectra of the separated samples. In this work, we propose to use lanthanum fluoride fine particles as a new stationary phase of a TLC plate. The average size of LaF3 particles is around 100 nm. FTIR spectrum of the LaF3 particles has no interfering absorption. Preliminary TLC experiments show that mixtures of rhodamine B and methylene blue mixture can be successfully separated by this new TLC plate using LaF3 fine particles as a stationary phase. Methylene blue and rhodamine B from separated spot can be clearly detected by using in situ FTIR spectra.

Preparation and luminescence of europium-doped lanthanum fluoride–benzoic acid hybrid nanostructures

Europium-doped lanthanum fluoride (LaF3:Eu3+) nanoparticles were synthesized using a solvothermal method, and they were then capped with benzoic acid (BA) ligands to form LaF3:Eu3+–BA hybrid nanostructures. The LaF3:Eu3+–BA hybrid nanostructures showed strong luminescence as a result of energy transfer from BA to the Eu3+ ions of the LaF3:Eu3+ nanoparticles. The dominant excitation band for the LaF3:Eu3+–BA hybrid nanostructures ranged from 200nm to 300nm. It has been shown that the luminescence of LaF3:Eu3+–BA hybrid nanostructures strongly depends on the pH value and content of benzoic acid used in the preparation of the hybrid nanostructures. An X-ray diffraction technique, transmission electron microscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy and a UV–vis spectrophotometer were used to characterize the products.

Rapid determination of actinides in seawater samples

A new rapid method for the determination of actinides in seawater samples has been developed at the Savannah River National Laboratory. The actinides can be measured by alpha spectrometry or inductively-coupled plasma mass spectrometry. The new method employs novel pre-concentration steps to collect the actinide isotopes quickly from 80 L or more of seawater. Actinides are co-precipitated using an iron hydroxide co-precipitation step enhanced with Ti+3 reductant, followed by lanthanum fluoride co-precipitation. Stacked TEVA Resin and TRU Resin cartridges are used to rapidly separate Pu, U, and Np isotopes from seawater samples. TEVA Resin and DGA Resin were used to separate and measure Pu, Am and Cm isotopes in seawater volumes up to 80 L. This robust method is ideal for emergency seawater samples following a radiological incident. It can also be used, however, for the routine analysis of seawater samples for oceanographic studies to enhance efficiency and productivity. In contrast, many current methods to determine actinides in seawater can take 1–2 weeks and provide chemical yields of ~30–60 %. This new sample preparation method can be performed in 4–8 h with tracer yields of ~85–95 %. By employing a rapid, robust sample preparation method with high chemical yields, less seawater is needed to achieve lower or comparable detection limits for actinide isotopes with less time and effort.

Photodegradation of luminescence in organic-ligand-capped Eu3+:LaF3 nano-particles

The luminescence from europium doped lanthanum trifluoride (Eu3+:LaF3) nano-crystals can be greatly enhanced by capping with β-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm−2, the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms.

Investigation on Lanthanum Fluoride as a Novel Cathode Buffer Material Layer for the Enhancement of Stability and Performance of Organic Solar Cell

This article presents the investigation on very thin Lanthanum Fluoride (LaF3) layer as a new cathode buffer layer (CBL) for organic solar cell (OSC). OSCs were fabricated with poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) polymer blend at 1:1 ratio. Electron-beam evaporation at room temperature was used to deposit 3 and 5 nm thick LaF3 layer. A very smooth surface of LaF3 with an average roughness of 0.2 nm has been observed by the Atomic Force Microscope (AFM) that is expected to prevent diffusion of cathode metal ion through it and thereby enhance the lifetime and stability of OSC. Huge enhancement of JSC and VOC was also observed for 3 nm-thick LaF3 CBL. Several excellent features of the LaF3 layer such as, transporting electron through tunneling, blocking of holes to the cathode, minimizing recombination, protecting the photoactive polymer from ambient oxygen, and reducing degradation/oxidation of any low work function layer at the cathode interface, might have contributed to the performance enhancement of OSC. The experimental findings indicate the promise of LaF3 to be an excellent CBL material for OSC.

Lanthanum Fluoride Charge Trapping Layer with Silicon Nanocrystals for Nonvolatile Memory Device Application

Silicon nanocrystals (Si-NCs) embedded in a Lanthanum Fluoride (LaF3) insulating layer were fabricated as a charge trapping layer by a simple Chemical Bath Deposition (CBD) technique. The X-Ray diffraction of the deposited layer shows a polycrystalline LaF3 deposition on silicon. The charge storage behavior of Si-NCs embedded in the LaF3 layer have been investigated in metal-insulator-semiconductor (MIS) structures by electrical characterization, where various interface traps and defects were introduced by thermal annealing treatment. The flat-band voltage shift of capacitance-voltage (C–V) and conductance-voltage (G–V) curves of Si: NC-MIS devices were found to exhibit charge trapping. The current-voltage (I–V) measurement also demonstrate that traps have strong influence on the charge storage behavior, in which the traps and defects at the internal/surface of silicon nanocrystals and the interface states at the LaF3 /Si substrate play different roles, respectively. The flat-band voltage (VFB) shift was about 700 mV, which is agreed well enough to capture charge inside the nanoparticle for nonvolatile memory (NVM) device applications. Thickness-dependent flat-band voltage (VFB) shifts in the MIS structure which can be used as a low-voltage nonvolatile memory.

Photoluminescence of cerium fluoride and cerium-doped lanthanum fluoride nanoparticles and investigation of energy transfer to photosensitizer molecules.

CexLa1-xF3 nanoparticles have been proposed for use in nanoscintillator-photosensitizer systems, where excitation of nanoparticles by ionizing radiation would result in energy transfer to photosensitizer molecules, effectively combining the effects of radiotherapy and photodynamic therapy. Thus far, there have been few experimental investigations of such systems. This study reports novel synthesis methods for water-dispersible Ce0.1La0.9F3/LaF3 and CeF3/LaF3 core/shell nanoparticles and an investigation of energy transfer to photosensitizers. Unbound deuteroporphyrin IX 2,4-disulfonic acid was found to substantially quench the luminescence of large (>10 nm diameter) aminocaproic acid-stabilized nanoparticles at reasonable concentrations and loading amounts: up to 80% quenching at 6% w/w photosensitizer loading. Energy transfer was found to occur primarily through a cascade, with excitation of "regular" site Ce(3+) at 252 nm relayed to photosensitizer molecules at the nanoparticle surface through intermediate "perturbed" Ce(3+) sites. Smaller (<5 nm) citrate-stabilized nanoparticles were coated with the bisphosphonate alendronate, allowing covalent conjugation to chlorin e6 and resulting in static quenching of the nanoparticle luminescence: ∼50% at ∼0.44% w/w. These results provide insight into energy transfer mechanisms that may prove valuable for optimizing similar systems.

Preparation of lanthanum trifluoride nanoparticles surface-capped by tributyl phosphate and evaluation of their tribological properties as lubricant additive in liquid paraffin

LaF3 nanoparticles surface-capped by tributyl phosphate (denoted as TBP–LaF3) were prepared by in situ surface modification route. The size, morphology and phase structure of as-prepared TBP–LaF3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The thermal stability of as-synthesized TBP–LaF3 nanoparticles was evaluated based on thermogravimetric analysis, and their tribological properties as additive in liquid paraffin were evaluated with a four-ball friction and wear tester. Moreover, the morphology of worn steel surfaces was analyzed with a scanning electron microscope, and the composition and chemical state of typical elements on worn steel surfaces were examined with an X-ray photoelectron spectroscope. Results show that as-synthesized TBP–LaF3 nanoparticles possess good thermal stability and excellent anti-wear and load-carrying capacities as well as good friction-reducing ability. This is because, on the one hand, TBP as the surface-modifier is able to improve the dispersibility of LaF3 nanoparticles in liquid paraffin and allows good adsorption of LaF3 nanoparticles on sliding steel surfaces. On the other hand, active P element of TBP can form tribochemical reaction film on sliding steel surfaces. As a result, the boundary lubricating film consisting of adsorbed LaF3 nanoparticles and tribochemical reaction film results in greatly improved friction-reducing and anti-wear abilities as well as load-carrying capacity of the lubricant base stock and gives rise to significantly reduced friction and wear of the steel–steel sliding pair.

Preparation of Water-Soluble Lanthanum Fluoride Nanoparticles and Evaluation of their Tribological Properties

Water-soluble LaF3 nanoparticles surface-capped by two kinds of dialkyl polyoxyethylene glycol thiophosphate ester (denoted as DTP-10 and DTP-20) were synthesized via a surface-modification method. The morphology and microstructure of resultant surface-modified LaF3 nanoparticles (denoted as LaDTP-10 and LaDTP-20) were characterized by means of X-ray powder diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry, and their thermal stability was examined by thermogravimetric analysis. Moreover, the tribological properties of as-synthesized LaF3 nanoparticles as additives in distilled water were evaluated with a four-ball friction and wear tester, and the morphology of wear scar and the chemical states of some typical elements thereon were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. It has been found that as-prepared LaDTP-10 and LaDTP-20 nanoparticles have a size of 19.6 and 8.5 nm, respectively, and they have good dispensability in distilled water. Moreover, as-synthesized LaDTP-10 and LaDTP-20 nanoparticles as lubricant additives in distilled water exhibit good friction reducing, antiwear, and extreme pressure properties as well as high load-carrying capacity even at a concentration of 1 % (mass fraction). This is because LaF3 nanoparticles can be deposited on sliding steel surfaces to afford a surface protective layer, and they may also tribochemically react with rubbing steel surfaces to generate a boundary lubricating film mainly composed of phosphate, sulfide, sulfate, La2O3, and LaF3. Therefore, it is feasible for LaDTP-10 and LaDTP-20 nanoparticles to be used as water-soluble lubricant additives under harsh conditions.

High-pressure Synthesis and Characterization of the Rare-earth Fluoride Borate LaB2O4F

The rare-earth fluoride borate LaB2O4F was synthesized under high-pressure=high-temperature conditions of 1.1 GPa and 1300 °C in a Walker-type multianvil apparatus from lanthanum oxide, lanthanum fluoride, and boron oxide. The single-crystal structure determination revealed that LaB2O4F is isotypic to CeB2O4F. The compound crystallizes in the orthorhombic space group Pbca (no. 61) with eight formula units and the lattice parameters a = 8.2493(9), b = 12.6464(6), c = 7.3301(5) Å , V = 764.7(2) Å3, R1 = 0.0354, and wR2 = 0.0474 (all data). The structure exhibits a 9+1 coordinated lanthanum cation, one threefold coordinated fluoride ion and a chain of corner-sharing [BO3]3- groups. In addition to the IR- and Raman-spectroscopic investigations, DFT calculations were performed to support the assignment of the vibrational bands

Lanthanum Interaction with Surface Preparations

In latest integrated circuits’ generation, lanthanum has been commonly introduced to cap hafnium based high k gate oxides. Indeed it enables strong threshold voltage modulation of the devices. Nonetheless its implementation is challenging, especially during the gate patterning, where hydrofluoric acid is used to remove the high k film on the active areas. On the one hand, lanthanum is highly corrodible. On the other hand, it easily generates non soluble salts. Lanthanum fluoride salts are among the most stable ones. Preventing their deposition is hereby discussed. Hydrochloric acid is one of the best solutions to solubilize lanthanum, before removing the high k with hydrofluoric acid.

Effects of different ligands on luminescence properties of LaF3: Nd nanoparticles

A series of neodymium-doped lanthanum fluoride nanoparticles (NPs) were synthesized with hydrothermal method, and the effects of several ligands on the luminescence properties of the NPs were investigated. The X-ray diffraction (XRD) results indicated that the crystal phases of the modified NPs coincided with the standard spectrum. The transmission electron microscopy (TEM) showed that the samples were of similar size, shape and dispersibility. The infrared spectra suggested that the content of –OH groups as quenchers on the NPs surfaces decreased after modification. Compared with NPs modified by branched paraffin ligands, NPs conjugating ring-contained modifiers had less quenching effect and possessed stronger fluorescence intensity and longer fluorescence lifetime.

Photoluminescence of porous silicon coated by SILD method with LaF3 nanolayers

The method of lanthanum fluoride passivating layer synthesis in the matrix of porous silicon by successive ionic layer deposition was elaborated and optimized. Luminescence and FTIR of obtained structures demonstrate the crucial role of the chemical composition of silicon nanocrystallite surface in the formation of radiative recombination channels and in the stability of porous silicon photoluminescence. The combination of high optical transparency of LaF3 layers and low recombination losses in silicon covered with such layers allows to recommend the lanthanum fluoride film as an effective passivating coating for silicon optoelectronics devices.