Fabrication and luminescence of YF3:Tb3+ hollow nanofibers

YF₃:Tb³⁺ hollow nanofibers were successfully fabricated via fluorination of the relevant Y₂O₃:Tb³⁺ hollow nanofibers which were obtained by calcining the electrospun PVP/[Y(NO₃)₃ + Tb(NO₃)₃] composite nanofibers. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope, transmission electron microscope, and fluorescence spectrometer. YF₃:Tb³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 148 ± 23 nm. Fluorescence emission peaks of Tb³⁺ in the YF₃:Tb³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) (490, 543, 588, and 620 nm) of Tb³⁺ ions, and the ⁵D₄ → ⁷F₅ hypersensitive transition at 543 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Tb³⁺ hollow nanofibers were located in the green region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Tb³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Tb³⁺ ions and reached a maximum at 7 mol% of Tb³⁺. The possible formation mechanism of YF₃:Tb³⁺ hollow nanofibers was also discussed. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.     

Synthesis and luminescence properties of LaOCl:Eu3+ nanostructures via the combination of electrospinning with chlorination technique

LaOCl:Eu³⁺ nanofibers, nanobelts and nanotubes were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl as chlorinating agent. Different morphologies of LaOCl:Eu³⁺ were obtained via adjusting some of the electrospun parameters. X-ray powder diffraction analysis indicated that LaOCl:Eu³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameters LaOCl:Eu³⁺ nanofibers and nanotubes, and the width of LaOCl:Eu³⁺ nanobelts were respectively 198.64 ± 15.07, 168.86 ± 24.70 and 2.103 ± 0.3345 μm under the 95 % confidence level. Transmission electron microscope observation showed that as-obtained LaOCl:Eu³⁺ nanotubes were hollow-centered structure. Photoluminescence (PL) analysis manifested that the LaOCl:Eu³⁺ with different morphologies emitted the predominant emission peaks at 616 and 618 nm originating from the transition ⁵D₀ → ⁷F₂ of Eu³⁺ ions under the excitation of 283-nm ultraviolet light. It was found that the optimum molar ratio of Eu³⁺/(La³⁺+Eu³⁺) ions was 5 %. LaOCl:Eu³⁺ nanobelts exhibited the strongest PL intensity of the three morphologies under the same doping concentration. CIE analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Eu³⁺ ions and morphologies of nanomaterials, which could be applied in the fields of optical telecommunication and optoelectronic devices. The possible formation mechanisms of LaOCl:Eu³⁺ nanofibers, nanobelts and nanotubes were also proposed.     

Preparation and luminescent properties of YVO4:Eu3+ nanofibers by electrospinning

This paper describes a procedure based on electrospinning for generating europium-doped yttrium vanadate (YVO4:Eu3+) nanofibers with diameters ranging from 30 to 50 nm. The YVO4:Eu3+ nanofibers were obtained through calcining precursory nanofibers, which were prepared through the electrospinning method. Suitable electrospinning parameters, such as concentration of PVP in solution, spinneret tip-to-collector plate distance (TCD), and applied voltage between spinneret and collector plate, are used to obtain thinner and more uniform precursory nanofibers of YVO4:Eu3+, which is important for preparing smaller diameter pure YVO4:Eu3+ nanofibers. The luminescent properties of the YVO4:Eu3+ nanofibers including excitation and emission spectra and fluorescence lifetime were studied. The excitation spectrum shows a broad band extending from 200 to 350 nm, which corresponds to the strong vanadate absorption in YVO4:Eu3+. The emission spectrum is dominated by the red 5D0 --> 7F2 hypersensitive transition of Eu3+. The fluorescence lifetime of Eu3+ 5D0 --> 7F2 (619 nm) is determined to be 493 micros at room temperature, which is basically in accordance with that in the bulk (521 micros).     

Fabrication and characterization of FePt magnetic nanofibers via electrospinning technique

L1₀-structured platinum–iron (FePt) nanofibers were successfully synthesized by electrospinning technique, followed by calcination and reduction processes. In the preparation procedure, ferrous chloride tetrahydrate [Fe(Cl)₂?4H₂O] and iron nitrate nonahydrate [Fe(NO₃)₃?9H₂O] were, respectively, used as iron sources contained in precursor solution for electrospinning. Subsequently, the FePt nanofibers were obtained from the calcination in air and the followed reduction in hydrogen (H₂) of the as-spun FePt/PVP composite nanofibers. The FePt nanofibers were characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, and superconducting quantum interference device magnetometry. It was found that the different iron salt used in the spinning solutions could highly affect the FePt nanofiber morphology, crystallite size, and the magnetic properties. The FePt nanofibers, resulted from the spinning solution containing iron dichloride tetrahydrate, were of better crystallinity and well-defined fibrous morphology with an average diameter of about 110 nm. Additionally, the considerably large coercivity of 10.27 kOe was recorded from the above FePt nanofibers.     

Synthesis of Y2O2S:Eu3+ luminescent nanobelts via electrospinning combined with sulfurization technique

Y₂O₂S:Eu³⁺ nanobelts were successfully prepared via electrospinning method and sulfurization process using the as-prepared Y₂O₃:Eu³⁺ nanobelts and sulfur powders as sulfur source by a double-crucible method for the first time. X-ray diffraction analysis indicated that the Y₂O₂S:Eu³⁺ nanobelts were pure hexagonal in structure with space group P $ \bar{3} $ m1. Scanning electron microscope images showed that the width and thickness of the Y₂O₂S:Eu³⁺ nanobelts were ca. 6.7 μm and 125 nm, respectively. Under the excitation of 325-nm ultraviolet light, Y₂O₂S:Eu³⁺ nanobelts exhibited red emissions of predominant peaks at 628 and 618 nm, which are attributed to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ions. It was found that the optimum doping concentration of Eu³⁺ ions in the Y₂O₂S: Eu³⁺ nanobelts was 3 %. Compared with bulk particle, Eu³⁺–O^2?/S^2? charge transfer bands (260 and 325 nm) of the Y₂O₂S:Eu³⁺ nanobelts showed a blue-shift significantly. The formation mechanism of the Y₂O₂S: Eu³⁺ nanobelts was also proposed. This new sulfurization technique is of great importance, not only to inherit the morphology of rare earth oxides but also to fabricate pure-phase rare earth oxysulfides at low temperature compared with conventional sulfurization method.     

Preparation and luminescence properties of La6MoO12:Eu3+/PVA nanofibers by Pechini/electrospinning process

The 20% concentration Eu3+-based red-emitting phosphor, nano-sized La6MoO12:Eu3+ was prepared by the Pechini method. X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), photoluminescence (PL), and decay curves were used to characterize the resulting samples. The phosphor can be efficiently excited by near UV light and exhibits an intense red luminescence corresponding to the electric dipole transition 5D0 --> 7F2 at 615 nm. When the phosphor was mixed into poly(vinyl alcohol) aqueous solution, the fluorescent nanofibers could be prepared by electrospinning process. It was suggested that the La6MoO12:Eu3+ phosphor would be a promising red component for solid-state lighting devices based on InGaN or GaN light-emitting diodes.     

Fabrication of refining mesoporous silica nanofibers via electrospinning

Refining mesoporous silica nanofibers were fabricated by electrospinning method. A triblock copolymer (Pluronic, P123, H(C₂H₅O)₂₀(C₃H₇O)₇₀(C₂H₅O)OH) was used as the structure direction agent and polyvinyl pyrrolidone (PVP) was employed to prepare refining nanofibers. SEM images showed that the refining fibers had an average diameter about 200-300 nm with smooth surface. FT-IR spectrum and TGA curve proved that P123 and PVP were removed from the fibers after a thermal treatment. It was found that the obtained silica nanofibers had mesoporous structure. The pore structures were characterized by XRD and the N₂ adsorption-desorption isotherm.     

Eu3+ concentration effect on luminescence properties of YAG:Eu3+ nanoparticles

Nanocrystalline Eu³⁺-doped YAG powders were prepared by modified Pechini method. The structural properties were investigated with XRD, SEM and Raman spectroscopy. XRD pattern indicated that the phase-pure YAG:Eu³⁺ crystallites were obtained without the formation of any other phases. Raman spectrum revealed good homogeneity and crystallinity of synthesized nanopowders. The luminescent properties were studied by measurement of excitation and emission spectra, quantum yields and decay curves. The effect of Eu³⁺ concentration on ⁵D₀ level lifetime was studied. The processes resulting in the relaxation of excited state (⁵D₀ level) were discussed and the probabilities of radiative and nonradiative processes were calculated using the model of f–f transition intensities. It was found that the observed shortening of ⁵D₀ level lifetime with Eu concentration is caused by increase of nonradiative process probability.     

Upconversion luminescence properties of YF3:Yb3+, Er3+ nanoclusters

The synthesis, characterization, and spectroscopy of upconverting Yb3+/Er3+ codoped YF3 rod-like nanoclusters are presented. The YF3 nanoclusters were synthesized by a simple hydrothermal method. The clusters structure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Under 978 nm laser excitation, stronger blue (4F(5/2) --> 4I(15/2) and 2p(3/2) --> 4I(11/2)) and green (4S(3/2), 2H(11/2) --> 4I(15/2)) upconversion luminescence were observed at 978 nm. The measured intensity of upconversion luminescence was different when pump power changed, which shows that the blue and green upconversion luminescence come from three-photon and two-photon energy transfer processes, respectively.     

Fabrication of multi-walled carbon nanotube reinforced polyelectrolyte hollow nanofibers by electrospinning

Hybrid hollow multi-walled carbon nanotubes (MWCNTs)/polyelectrolytes (PE) nanofibers were prepared by a combination of the electrospinning method and layer-by-layer (LbL) technique. The mixed polystyrene (PS)/MWCNTs nanofibers were obtained by electrospinning method, which were employed as templates to self-assembly multilayered polyelectrolytes by LbL technique. Hollow MWCNTs/PE nanofibers were obtained by selectively removed part of the template: PS, which is confirmed by Raman spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Fabrication of magnetic-luminescent bifunctional composite nanofibers via facile electrospinning

Fe₃O₄/Eu(BA)₃phen/polyvinyl pyrrolidone (PVP) magnetic-luminescent bifunctional composite nanofibers have been successfully fabricated based on ferroferric oxide (Fe₃O₄) nanoparticles (NPs) and europium complexes Eu(BA)₃phen (BA = benzoic acid, phen = phenanthroline) via electrospinning technology. The as-prepared samples were characterized by X-ray diffractometry, field-emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, fluorescence spectroscopy and vibrating sample magnetometry. The as-prepared Fe₃O₄/Eu(BA)₃phen/PVP composite nanofibers possess good fibrous morphology, and Fe₃O₄ NPs are evenly dispersed into nanofibers. Under the excitation of 274-nm ultraviolet light, Fe₃O₄/Eu(BA)₃phen/PVP composite nanofibers exhibit red emissions of predominant peaks at 592 and 616 nm, which are respectively attributed to the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ energy levels transitions of Eu³⁺ ions. The optimum mass percentage of Eu(BA)₃phen to PVP is 15 %. The fluorescence intensity of composite nanofibers is decreased when more Fe₃O₄ NPs were added. The saturation magnetization is increased with the increase of Fe₃O₄ NPs, indicating that the magnetism of the composite nanofibers can be tuned by adjusting Fe₃O₄ NPs content. The magnetic-luminescent bifunctional composite nanofibers are expected to apply in the fields of cell separation and biological labeling imaging, etc.     

Preparation and the luminescent properties of Tb3+-doped Gd2O3 fluorescent nanofibers via electrospinning

Tb(3+)-doped Gd(2)O(3) (Gd(2)O(3):Tb(3+)) nanofibers were prepared via a simple electrospinning technique using poly(ethylene oxide) (PEO) and rare-earth acetate tetrahydrates (Ln(CH(3)COO)(3)·4H(2)O (Ln = Gd, Tb)) as precursors. The obtained nanofibers have an average diameter of about 80 nm and are composed of pure cubic Gd(2)O(3) phase. A possible formation mechanism for the nanofibers is proposed on the basis of the experimental results, which reveals that PEO acts as the structure directing template during the whole electrospinning and subsequent calcination process. The luminescent properties of the nanofibers were investigated in detail. The nanofibers exhibit a favorable fluorescent property symbolized by the characteristic green emission (545 nm) resulting from the 5D4-->7F5 transition of Tb(3+). Concentration quenching occurs when the Tb(3+) concentration is 3 at.%, indicating that the Gd(2)O(3):Tb(3+) nanofibers have an optimum luminescent intensity under such a doping concentration.     

Synthesis and luminescence properties of ZnO:Eu3+ nano crystalline via a facile solution method

Different ZnO:Eu3+ nanocrystalline were obtained from a facile solution method with two different precipitators. The comparison of photoluminescence property of two different ZnO:Eu3+ nanocrystalline was performed. The XRD patterns and the PL spectra indirectly indicate that the dopant Eu3+ ions had entered into the crystal lattices of ZnO. The study on the PL spectra of the as-prepared ZnO:Eu3+ nanocrystalline shows that with the change of dopant concentration, the ratio of relative emission intensity of electric dipole transition to magnetic dipole transition changes, which fully expresses that the presence of the inversion centers is associated with the dopant concentration of Eu3+.     

Fabrication of WO3 nanofibers by high voltage electrospinning

Mixtures of 0.1, 0.3, and 0.5 mmol ammonium metatungstate hydrate (AMH), and poly (vinyl alcohol) (PVA) were electrospun by a + 20 kV direct voltage to synthesize fibers. Those of 0.5 mmol AMH were further calcined to have PVA removed and crystalline degree improved. At 500 °C and 2 h calcination, WO₃ nanofibers, including two main stretching modes, 3.24 eV direct energy gap, and 378 nm wavelength violet emission were detected. A possible formation mechanism of WO₃ nanofibers was proposed according to the experimental results.     

Influence of the Eu3+ dosage concentration on luminescence properties of YPO4:Eu3+ microspheres

In this study, YPO₄:Eu³⁺ microspheres with different Eu³⁺ dosage concentration were fabricated by a facile hydrothermal route at 200 °C for 10 h in the presence of citric acid. The YPO₄:Eu³⁺ samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and luminescence spectroscopy. The XRD results reveal that the YPO₄:Eu³⁺ samples presented a tetragonal structure. The TEM and SEM observations demonstrate that the YPO₄:Eu³⁺ samples with uniform sphere-like morphologies can be obtained at 200 °C for 10 h. The sizes of samples are in the range of 2–2.2 μm. The room temperature luminescence properties of YPO₄:Eu³⁺ samples were studied using an excitation wavelength of 227 nm. The emission spectrum displays the bands associated to the ⁵D₀ → ⁷F_J (J = 1, 2 and 4) electronic transitions characteristics of the Eu³⁺ cations at different positions. The influence of Eu³⁺ dosage concentration on luminescence properties of YPO₄:Eu³⁺ microspheres were studied carefully.     

Photoluminescent properties of Eu3+ doped electrospun CeO2 nanofibers

In this study, CeO₂ nanofibers and that doped with Eu³⁺ were prepared via a facile electrospinning route and annealed at different temperatures ranging from 500 to 900 °C. Their structures were investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoluminescence properties of the nanofibers were studied in detail. It was found that the nanofibers with Eu% concentration of 0.67 mol.% and annealed at 700 °C exhibited the highest intensities of the luminescence peaks between 550 and 650 nm.     

并列型静电纺丝法制备扭曲螺旋结构的复合微/纳米纤维与表征

采用并列型静电纺丝法成功制备出新型的扭曲螺旋结构的复合微/纳米纤维.主要使用扫描电镜、Smile View图像分析软件对样品的微观形貌及结构进行了表征和分析.分析结果表明,高收缩性聚酯弹性体TPEE和相对收缩率较低的PBT,在并列型电纺过程中因断裂伸长率不同产生不同程度的收缩,从而形成三维扭曲螺旋结构的复合纤维.所得纤...     

Enhanced the structure and optical properties for ZnO/PVP nanofibers fabricated via electrospinning technique

Zinc oxide/polyvinylpyrrolidone (ZnO/PVP) nanocomposite fibers with enhanced structural, morphological and optical properties were purposefully tailored using electrospinning technique. Meanwhile, ZnO nanoparticles (NPs),with particle size of ~50 nm, were synthesized using a co-precipitation method. The nanocomposite fibers were prepared by an electrospun solution of PVP containing ZnO NPs of 2, 4, 6 and 8 wt%. Evidently, the morphological, thermal and optical properties of the ZnO/PVP nanocomposite fibers were enhanced by dispersing ZnO NPs into PVP fibers. Typically, controlling the ZnO NPs content and their dispersibility (0–8 wt%) into PVP fibers result in improved the thermal stability (an increase of onset decomposition temperature by ~120 °C above pure PVP fibers) as well as the UV–Vis protection (reduction in UV transmission by 70%) and the photoluminescence properties (a sharp UV emission around 380 nm) Overall, based on the enhanced properties, the PVP/ZnO nanocomposite fibers can be considered a promise material in optoelectronic sensors and UV photoconductor.