Study On Electrospinning Synthesis And Properties Of Eu³⁺ Or Tb³⁺ Doped GdBO₃and LuBO₃Nanofibers

One-dimensional nanostructures, such as nanowires, nanorods, nanobelts,nanotubes and nanofibers, are defined as two-dimensional directions at nanomentersscale. Quantum effect in one-dimensional nanomaterials plays an important role, andtheir physical and chemical properties, such as thermal transport mechanisms, aresignificantly different from the bulk materials.Electrospinning represents a simple and convenient method for preparing ceramicfibers with both solid and hollow interiors that are exceptionally long, uniform indiameter ranging from tens of nanometers to several micrometers, and diversified incompositions. In recent years, many research institutes from both home and abroadsynthesized a variety of inorganic nanofibers by electrospinning method, such assemiconductor, rare earth luminescent, batteries, and catalytic fibers. In this paper,rare earth borate, ZnFe₂O₄and ZnO:Fe nanofibers were prepared by electrospinningcombined with heat treatment. We used as the theoretical basis of the spectralcharacteristics of the rare earth ions, energy transfer and transport, and the exchangeinteraction, and investigate how fibers morphology, crystal structure, size and surfaceaffect luminescence property, fluorescence lifetime and magnetism of the samples.1. GdBO₃: Ln³⁺（Ln=Eu,Tb） nanofibersGdBO₃:Ln³⁺（Ln=Eu, Tb） nanofibers were synthesized by electrospinningtechnique combined heat treatment. XRD results indicate the fibers sample calcined at800°C can be in accord with the characteristic peaks of GdBO₃phase. The obtainedGdBO₃:Ln³⁺nanofibers are flexible and rough with an average diameter ofapproximately150nm. The emission spectrum of GdBO₃:Eu³⁺nanofibers consists ofan orange emission at593nm and red emission at612and626nm. The R/O value is0.57, which is lower than those in previous reports. Fewer surface defects, holes, andinterface phase for the fibers sample enhance the symmetry of the crystal field aroundEu³⁺, thereby yielding a high orange emission. When the molar ratio of the starting material Gd（NO₃）3and H₃BO₃is1:1, the product deviate from the initialstoichiometric ratio to obtain new Gd₃BO₆phase. The emission spectrum ofGd₃BO₆:Eu³⁺nanofibers showed the5D0â†'7F2transition is dominant. For color purity,Gd₃BO₆:Eu³⁺nanofibers reflect the superior chromaticity. The difference betweendoping Eu³⁺and Tb³⁺may be attributed to the relative intensities of the orange andred emissions of Eu³⁺, which are sensitive to local symmetry. The anisotropy andspace dimensionality of the sample can affect the local environment surrounding theEu³⁺ions. The blue to green ratio of Tb³⁺depend on the cross relaxation between Tb³⁺ions.2. LuBO₃:Ln³⁺（Ln=Eu,Tb） nanofibersTb doped LuBO₃nanocrystallines were prepared by sol-gel methods, XRD resultsshow that the doping Tb ions reduce the crystalline temperature of LuBO₃andimprove crystal quality. The crystallinity process of the solid materials is formed bythe atom diffusion. Tb³⁺ions substitution Lu³⁺ions in crystal lattice, which inevitablylead to the change of the charge density and the distortion of the electron cloud.Combination reactions will more easily occur between the anion and Lu ions.LuBO₃:Ln³⁺（Ln=Eu, Tb） nanofibers were synthesized by electrospinningtechnique combined heat treatment. LuBO₃:Ln³⁺（Ln=Eu,Tb） nanofibers can beobtained by sintering the electrospun composite fibers at800-900°C for2h. Theas-prepared nanofibers exhibit porous morphology and have the average diameters of200-300nm, which consist of closely lined nanoparticles with the size of about30nm.The high R/O values of LuBO₃:Eu³⁺nanofibers are much higher than that ofnanoparticles synthesized by sol-gel methods. The nanoscale porous morphologypossesses higher surfaces area, resulting in a high degree of disorder near the surfaces.The sites at the surfaces of the porous nanofibers are of low site symmetry, therebyyielding a high R/O value. the emission intensities and the fluorescence lifetimeincrease slightly with increasing Tb³⁺concentration, and its fluorescence lifetime issignificantly longer than that reported in previous literature. The porous structureslead to the most Tb³⁺ions residing on the surface, improving the energy transferefficiency between adjacent Tb³⁺ions. 3. Oxide containing zinc nanofibersZnFe₂O₄nanofibers were prepared using electrospinning technique combiningwith heating treatment at high temperature. XRD results indicate that diffractionpeaks of as-prepared nanofibers are very close to the standard pattern of ZnFe₂O₄（PCPDF82-1049）, which possess cubic spinel structure. The morphologies offiber before and after the sintering show significant differences. The diameter ofnanofibers decreased remarkably and morphology becomes rough and porous.ZnFe₂O₄micro/nano fibers at the room temperature display paramagnetic character.The room temperature ferromagnetic behavior was observed in Zn_0.8Cu_0.2Fe₂O₄nanofibers. Their residual magnetization was1.018emu/g, and coercivity was54.585Oe. Dopants Cu ions can replace Zn or Fe in the substitutional sites, Cu ionshave strong preference for B-sites, more and more Fe³⁺ions will start migrating fromA to B-sites, resulting in decrease of the B-B interaction and increase of the A-Binteraction. Thus, Zn_0.8Cu_0.2Fe₂O₄nanofibers possess room temperature ferromagneticproperties. Upon Xe lamp irradiation,95%of RhB could be removed in120minirradiation when ZnFe₂O₄nanoparticles were added. ZnFe₂O₄micro/nano fibers havelarge surface area, which accelerates the reaction speed and efficiency.Fe doped ZnO nanofibers are successfully synthesized via electrospinningmethods. XRD results indicate that the fiber samples calcined at520℃correspond tohexagonal wurtzite structure of ZnO. SEM images display that the precursornanofibers were relatively continuous and uniform. After heating treatment, themorphology of ZnO:Fe nanofibers show structure distortion such as wrinkles orcollapsing, and the average diameter decreases mainly100nm. When Feconcentration up to5%, the solubility of Fe³⁺in ZnO incline to saturation, Fe ionseasily entering into interstitial position of ZnO lattice will form interstitial solidsolution of Fe2O₃-ZnO, which result in decrease VOconcentration, green-lightintensity abruptly reduced to minimum. M-H curves of Fe doped ZnO nanofibers atdifferent concentrations show saturation, reflecting room temperature ferromagnetism.When the Fe concentration is low, Fe³⁺ions substitute Zn²⁺in ZnO crystal lattice.This will produce large amounts of Zn²⁺vacancies, enhancing the effect of the exchange interaction between Fe ions.