Yttrium Fluoride Research Articles

Controllable synthesis, formation mechanism and upconversion luminescence of β-NaYF4 : Yb3+/Er3+ microcrystals by hydrothermal process

Hexagonal sodium yttrium fluoride crystals with predictable shapes, such as microtubes, microspheres, microrods, micro-bipyramids, microplates, and microprisms, have been synthesized by simply tuning the molar ratio of NaF to RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Yb3+, Er3+). The structural and kinetic factors that govern the phase and shape evolution of NaYF4 crystals have been carefully studied, and the influence of NaF to RE3+ ratio on phase and morphology evolution was systematically investigated and discussed. It is found that the molar ratio of NaF to RE3+ can strongly control the size and structure of as-prepared β-NaYF4 : Yb3+/Er3+ samples owing to the difference of capping effect of F− on the different crystal planes of β-NaYF4 microcrystals. By choosing bipyramidal β-NaYF4 microdisks as a candidate, the possible formation mechanism was proposed on the basis of XRD analysis and SEM observation of the products at the different reaction time periods. Most interestingly, the upconversion (UC) luminescent properties of β-NaYF4 crystals show that the optical properties of as-synthesized materials with different morphologies exhibit great distinction. This study is expected to be suggestive for the precisely controlled growth of other complex rare earth fluoride compounds and provide a reference for exploration of the morphology-dependent UC luminescence properties.

Optimization of synthesis of upconversion luminescence material NaYF4:Er3+,Yb3+ nanometer-phosphor by low-temperature combustion synthesis method

A kind of Er3+-Yb3+ co-doped natrium yttrium fluoride nanometer-phosphor sensitive to 980 nm was synthesized by the low-temperature combustion synthesis method, which expanded the application range of the low-temperature combustion synthesis (LCS) method which is always used in the synthesis of oxides and compound oxides. The synthesis conditions were optimized with orthogonal experiments and the optimum technological parameters were obtained. Intense upconversion emissions at 522, 540 and 653 nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground state were observed when excited by continuous wavelength (CW) laser radiation at 980 nm. The effect of the carbamide amount on the phase formation and the luminescence intensity was analyzed. The average particle size of the sample was 30–40 nm.

Controlled synthesis and formation mechanism of sodium yttrium fluoride nanotube arrays

Cubic and hexagonal sodium yttrium fluoride were successfully synthesized from yttrium nitrate, sodium fluoride and polyethanediol in propanetriol solvent under a facile hydrothermal route. By regulating the molar ratio of yttrium and fluoride, hydrothermal temperature and reaction time, the phase and shape of sodium yttrium fluoride were commendably controlled. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS) techniques. It was revealed that the hollow-structured Na(Y1.5Na0.5)F6 nanotubes self-assembled and arrayed orientedly to be bamboo raft-shaped. The formation of hexagonal Na(Y1.5Na0.5)F6 nanotube arrays was attributed to solid-liquid-solid process and Oswald ripening. This study provided a simple method to prepare hexagonal bamboo raft-shaped Na(Y1.5Na0.5)F6 on a large scale, which broadened their practical applications.

Synthesis and luminescent characteristics of submicron powders on the basis of sodium and yttrium fluorides doped with rare earth elements

Submicron powders of solid solutions on the basis of cubic and hexagonal phases existing in a NaF-YF3 system have been synthesized with the precipitation method from aqueous solutions at room temperature. The conditions for the preparation of single-phase samples have been determined. The upconversion luminescence spectra were investigated. The most promising composition is revealed (Na0.414Ca0.183Y0.215Yb0.094Er0.094F1.989), which demonstrates an upconversion luminescence quantum yield of 1.9% with a 3-W pump power at a 974-nm wavelength.

Hydrothermal synthesis, phase evolution, and optical properties of Eu3+-doped KF–YF3 system materials

Abstract

Ultra-high photoluminescent quantum yield of β-NaYF_4: 10% Er^3+ via broadband excitation of upconversion for photovoltaic devices

The upconversion photoluminescent quantum yield (PLQY) of erbium-doped hexagonal sodium yttrium fluoride (β-NaYF(4): 10% Er(3+) was measured under broadband excitation with full width half maxima ranging from 12 to 80 nm. A novel method was developed to increase the bandwidth of excitation, while remaining independent of power via normalization to the air mass 1.5 direct solar spectrum. The measurements reveal that by broadening the excitation spectrum a higher PLQY can be achieved at lower solar concentrations. The highest PLQY of 16.2 ± 0.5% was achieved at 2270 ± 100 mW mm(-2) and is the highest ever measured.

Hexagonal NaYF<sub>4</sub> Nanotube Arrays Obtained via Solvothermal Process

Hexagonal sodium yttrium fluoride has been successfully synthesized via a facile solvothermal route, using yttrium nitrate, sodium fluoride and polyethanediol as raw materials to react in propanetriol solvent. The as-prepared product was characterized by powder X-ray diffraction, scanning electron microscopy, thermogravimetric and differential thermal analysis, Fourier transform infrared spectrum and energy dispersive X-ray spectrum. The characterization results revealed that the products are hexagonal and denoted as NaYF4. The as-synthesized hexagonal sodium yttrium fluoride composed of hollow-structured nanotubes self-assembled and arrayed orientedly to take on bamboo raft morphology. Hexagonal NaYF4 nanotube arrays exhibited high heat stability. This study provides a simple method to prepare bamboo raft-shaped NaYF4 in large scale, which broads their practical applications.

Facile preparation of hydrophilic sodium yttrium fluoride nanorods using hydrophobic nanospheres as precursor

Abstract

Co-precipitation of yttrium and barium fluorides from aqueous solutions

Co-precipitation of barium and yttrium fluorides from aqueous solutions at room temperature produced non-equilibrium Ba1−xYxF2+x nanofluoride phase with face-centered cubic crystal lattice of fluorite-type with the composition interval of the homogeneity for x=0.35–0.75. Lattice parameter a of this solid solution nanophase varied as a function of the sample chemical composition in a complex manner with two areas of linear dependency, from x=0.35 to 0.45 and from x=0.50 to 0.75. A plausible explanation of this phenomenon included a change of the type of crystal lattice defects and the manner of their population with the corresponding ions. An increase of the relative amount of yttrium in the HF reaction system led to the formation of hydroxonium salt of decafluorotriyttrium acid, (H3O+)Y3F10−·nH2O, instead of expected YF3 hydrate. No formation of oxyfluoride phases under acidic conditions has been observed.

Simulating condensation of ammonium fluoride during fluorination of yttria

The preparation of yttrium fluoride (YF3) by fluorination of yttria with ammonium bifluoride is an established process. During fluorination, large amounts of ammonium fluoride (NH4F) vapours are generated in the reaction zone. In order to prevent back reaction, the vapours must be suitably removed from the reaction zone. In usual practice, gas purging (argon or dry air), at fairly high flowrate, removes the vapours suitably. The high flowrates have a considerable effect on the temperature inside the reactor. The ammonium fluoride vapours, transported with the inert gas, condense on the cooler regions of the reactor. The condensed vapours being highly corrosive attack the reactor wall. The present study attempts to address the above issue. A three-dimensional numerical heat transfer model has been developed for the fluorination reactor using a commercial software – Fluent 6·1. The simulations were attempted with varying argon flow velocities, to identify the heat taken away by argon during the reaction. When surface cooling was applied, condensation of ammonium fluoride vapours occurred on the inner surface of the walls irrespective of the argon flow velocity; the simulated results for the extent of condensation from the exit end of the reactor were in fair agreement with the corresponding experimental results.

Upconversion polymeric nanofibers containing lanthanide-doped nanoparticles via electrospinning

Flexible and freestanding poly(methyl methacrylate) nanofibers containing the upconversion nanoparticles (UCNPs) of lanthanide-doped sodium yttrium fluoride have been successfully fabricated via an electrospinning process. The UCNPs in nanofibers commonly formed chain-like aggregates aligned along the fiber axes. The effect of the electrospinning process on the upconversion properties of the embedded UCNPs was explored by characterizing the time evolution of the upconversion emission following pulsed near-infrared excitation. Our study revealed that there is only a slight reduction of upconversion efficiency for the UCNPs in electrospun nanofibers, indicating that upconversion properties of the UCNPs are largely preserved in the nanofibrous films. The prepared upconversion nanocomposites (in the form of nanofibrous films) with controlled morphologies, structures, and properties could be useful for broad photonic applications.

Rare-Earth Doped Nanoparticles in Security Printing Applications

ABSTRACTIn this work, lanthanide-doped, sodium yttrium fluoride nanocrystals were prepared and dispersed in a solvent consisting of 90 vol% toluene and 10 vol% methyl benzoate. Poly (methyl methacrylate) polymer was dissolved in the solvent, in addition to the nanocrystals. Inks were printed using direct-write techniques. Substrates used included Kapton®, bond paper, metal and glass. Stencil patterns and QR codes were printed with these inks. An overview of direct write printing for security applications is given. On many substrates, these printed traces are difficult to detect in ambient lighting, but can be easily read using near-infrared (NIR) illumination, making them very useful for covert and semi-covert security printing applications.

Plasmon-enhanced upconversion fluorescence in NaYF4:Yb/Er/Gd nanorods coated with Au nanoparticles or nanoshells

We investigate plasmon-enhanced upconversion (UC) fluorescence in Yb3+-Er3+-Gd+3 codoped sodium yttrium fluoride (NaYF4:Yb/Er/Gd) nanorods using gold nanoparticles or nanoshells. A simple method was proposed for the preparation of core/shell NaYF4/Au structures, with dispersed Au nanoparticles or uniform Au coating on the surface of the UC nanorod. Pure hexagonal-phase NaYF4:Yb/Er/Gd nanorods were synthesized via a liquid-solid reaction in oleic acid and ethanol solvent. A one-step approach was introduced to modify the hydrophobic surfaces of the as-deposited NaYF4:Yb/Er/Gd nanorods. After this surface modification, Au nanoparticles or nanoshells were successfully attached on the surfaces of NaYF4:Yb/Er/Gd nanorods. The as-deposited UC nanorods showed a strong UC emission in green and red bands under 980 nm laser excitation. The attachment of Au nanoparticles onto NaYF4:Yb/Er/Gd nanorods resulted in a more than three-fold increase in UC emissions, whereas the formation of continuous and compact Au shells around the nanorods suppressed the emissions. The related interaction mechanisms of the UC emission of NaYF4:Yb/Er/Gd nanorods with plasmon modes in Au nanostructures are analyzed and discussed.

Lanthanide-doped ultrasmall yttrium fluoride nanoparticles with enhanced multicolor upconversion photoluminescence

Ultrasmall upconversion (UC) nanoparticles with efficient multicolor photoluminescence (PL) are quite desirable for high contrast in vitro and in vivo bioimaging. Here, we present a simple and reproducible thermolysis approach to synthesize 3.7 nm sized lanthanide-doped YF3 UC nanocrystals. The PL intensity of these ultrasmall nanoparticles was found to be about ten times brighter than that of 4.5 nm sized CaF2 counterparts, which were reported to be one of the smallest efficient upconversion nanoparticles. We also showed that the color output of these nanocrystals can all be simply modulated by adjusting the sensitizer Yb3+ concentration. Moreover, to further enhance the PL output, a one nm thick epitaxial layer was grown onto the YF3 nanocrystals. These lanthanide-doped ultrasmall upconversion YF3 nanocrystals with modulated and enhanced multicolor output are ideal for a variety of in vitro and in vivo biological imaging applications.

Antibacterial and antibiofilm properties of yttrium fluoride nanoparticles

Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. Moreover, colonization of abiotic surfaces by microorganisms and the formation of biofilms is a major cause of infections associated with medical implants, resulting in prolonged hospitalization periods and patient mortality. In this study we describe a water-based synthesis of yttrium fluoride (YF3) nanoparticles (NPs) using sonochemistry. The sonochemical irradiation of an aqueous solution of yttrium (III) acetate tetrahydrate [Y(Ac)3 · (H2O)4], containing acidic HF as the fluorine ion source, yielded nanocrystalline needle-shaped YF3 particles. The obtained NPs were characterized by scanning electron microscopy and X-ray elemental analysis. NP crystallinity was confirmed by electron and powder X-ray diffractions. YF3 NPs showed antibacterial properties against two common bacterial pathogens (Escherichia coli and Staphylococcus aureus) at a μg/mL range. We were also able to demonstrate that antimicrobial activity was dependent on NP size. In addition, catheters were surface modified with YF3 NPs using a one-step synthesis and coating process. The coating procedure yielded a homogeneous YF3 NP layer on the catheter, as analyzed by scanning electron microscopy and energy dispersive spectroscopy. These YF3 NP-modified catheters were investigated for their ability to restrict bacterial biofilm formation. The YF3 NP-coated catheters were able to significantly reduce bacterial colonization compared to the uncoated surface. Taken together, our results highlight the potential to further develop the concept of utilizing these metal fluoride NPs as novel antimicrobial and antibiofilm agents, taking advantage of their low solubility and providing extended protection.

Evolution of yttrium trifluoroacetate during thermal decomposition

A detailed analysis of the thermal decomposition of yttrium trifluoroacetate under different atmospheres is presented. Thermogravimetry, differential thermal analysis, and evolved gas analysis have been used for this in situ analysis. Solid residues at different stages have been characterized by means of X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The first decomposition stage (310 °C) is exothermic and involves the complete removal of carbon (organic part) and the formation of yttrium fluoride. This process is characterized by a fast mass loss rate. Afterwards, yttria (Y2O3) is formed at 1200 °C through a slow process controlled by the out diffusion of fluorine that involves the formation of yttrium oxyfluoride as an intermediate. The evolution of the mass during the decomposition and the structure of the yttria particles is not affected by the presence of oxygen or water. However, when the oxygen (water) partial pressure is as low as 0.02% (<0.002%), the kinetics and final particle structure are strongly affected.

Structural investigation of thorium in molten lithium–calcium fluoride mixtures for salt treatment process in molten salt reactor

X-ray absorption fine structure (XAFS) measurements on thorium fluoride in molten lithium–calcium fluoride mixtures and molecular dynamics (MD) simulation of zirconium and yttrium fluoride in molten lithium–calcium fluoride mixtures have been carried out. In the molten state, coordination number of thorium ( N i ) and inter ionic distances between thorium and fluorine in the first neighbor ( r i ) are nearly constant in all mixtures. However the fluctuation factors (Debye–Waller factor ( σ 2) and C 3 cumulant) increase until xCaF 2 = 0.17 and decrease by addition of excess CaF 2. It means that the local structure around Th 4+ is disordered until xCaF 2 = 0.17 and stabilized over xCaF 2 = 0.17. The variation of fluctuation factors is related to the number density of F − in ThF 4 mixtures and the stability of local structure around Th 4+ increases with decreasing the number density of F − in ThF 4 mixtures. This tendency is common to those in the ZrF 4 and YF 3 mixtures. However, in the case of YF 3 mixtures, the local structure around Y 3+ becomes disordered until xCaF 2 = 0.40 and it becomes stabilized by addition of excess CaF 2. The difference between ThF 4 mixtures and YF 3 mixtures is related to the difference of Coulumbic interaction between Th 4+–F − and Y 3+–F −. Therefore, the variation of local structure around cation is related to not only number density of F − in molten salts but also the Coulumbic interaction between cation and anion.

Controllable synthesis and up-conversion properties of tetragonal BaYF5:Yb/Ln (Ln = Er, Tm, and Ho) nanocrystals

The nanocrystals (NCs) of tetragonal barium yttrium fluoride (BaYF5) doped 1mol% Ln3+ (Ln=Er, Tm, Ho) and 20mol% Yb3+ with different morphologies and sizes have been successfully synthesized through a facile hydrothermal method. The influences of pH values of the initial solution and fluorine sources on the final structure and morphology of the products have been well investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the size, structure and morphology of these samples prepared at different conditions. And it is found that BaYF5:Yb/Ln NCs prepared at pH value of 10 using NaBF4 as F− source have a uniform spherical morphology with average diameter of 25nm. Additionally, the up-conversion (UC) properties of Yb/Er, Yb/Tm, and Yb/Ho doped BaYF5 nanoparticles were also discussed. Under 980nm laser excitation, the BaYF5:Yb/Er, BaYF5:Yb/Tm, and BaYF5:Yb/Ho NCs exhibit green, whitish blue, and yellow green UC luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.

Yellow-Orange Upconversion Luminescence in NaYF&lt;sub&gt;4&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt;, Yb&lt;sup&gt;3+&lt;/sup&gt; Phosphor Synthesized by Microwave Combustion Method

Erbium and ytterbium co-doped sodium yttrium fluoride (NaYF4:Er3+,Yb3+) was synthesized by combusting in home microwave oven directly. The structure and morphology of the sample was characterized by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), and its upconversion luminescence properties were investigated in detail. Under 980nm semiconductor laser excitation, the color of upconversion luminescence of NaYF4:Er3+,Yb3+ was green and red, and its upconversion spectrum exhibited distinct emission peaks at 522, 543 and 652 nm, the emission appears yellow-orange to the naked eye. The law of luminescence intensity versus pump power proved that the intense green emission at 522 and 543 nm were from Er3+(2H11/2→4I15/2and4S3/2→4I15/2), and the weaker red emission at 652 nm was from Er3+(4F9/2→4I15/2), which belong to the two photon process.

Infrared-to-visible upconversion luminescence of Er 3+ doped barium–natrium–yttrium–fluoride phosphor

Infrared-to-visible upconversion luminescence has been investigated in Er 3+-doped barium–natrium–yttrium–fluoride phosphor (Ba x Na y Y z F 2 x+y+3 z+3 m :Er m ) with different cation concentrations. Intense upconversion emissions around 530, 550, and 660 nm corresponding to the 2H 11/2, 4S 3/2, and 4F 9/2 transitions, respectively to the 4I 15/2 ground state were observed when excited by CW laser radiation at 1550 nm. We adopted the low-temperature combustion synthesis (LCS) method to decrease the phosphor particle size to 40–70 nm in order to couple to the photosensitive surface of CCD. The effect of the amount of carbamide on the particle size and the upconversion luminescence intensity was analyzed. The upconversion luminescence mechanism was studied by the log–log plot of intensity–power.