Coaxial nanofibers to help achieve tunable and enhanced simultaneous magnetic-luminescent bifunctionality

A new nanostructure of CoFe₂O₄@Y₂O₃:5 %Tb³⁺ magnetic-luminescent bifunctional coaxial nanofibers has been successfully fabricated via electrospinning technology using a homemade coaxial spinneret. The morphologies, structures, magnetic and luminescent properties of the final products were investigated in detail by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and fluorescence spectroscopy. The results show the CoFe₂O₄@Y₂O₃:5 %Tb³⁺ magnetic-luminescent bifunctional coaxial nanofibers simultaneously possess superior magnetic and luminescent properties due to isolating Y₂O₃:5 %Tb³⁺ luminescence center from CoFe₂O₄ magnetic nanofibers. Furthermore, the luminescent intensity and color of the coaxial nanofibers can be tuned via adjusting the concentrations of rare earth ions. The bifunctional magnetic-luminescent CoFe₂O₄@Y₂O₃:5 %Tb³⁺ coaxial nanofibers have potential applications in biomedical area, such as drug-delivery systems, cell labeling and separation, enhancement for magnetic resonance imaging, and subsequent optical identification. More importantly, the design conception and construction technology are of universal significance to fabricate other bifunctional coaxial nanofibers.     

Coaxial electrospinning preparation and properties of magnetic–photoluminescent bifunctional CoFe2O4@Y2O3:Eu3+ coaxial nanofibers

CoFe₂O₄@Y₂O₃:Eu³⁺ magnetic–fluorescent bifunctional coaxial nanofibers have been successfully obtained via calcination of the [CoFe₂O₄/PVP]@[(Y(NO₃)₃ + Eu(NO₃)₃)/PVP] composite coaxial nanofibers which were fabricated by coaxial electrospinning technique. The diameter of CoFe₂O₄@Y₂O₃:5 %Eu³⁺ magnetic–fluorescent bifunctional coaxial nanofibers was 133 ± 17 nm. Strong fluorescence emission peaks of Eu³⁺ in the CoFe₂O₄@Y₂O₃:Eu³⁺ coaxial nanofibers were observed and assigned to ⁵D₀ → ⁷F₁ (588 nm), ⁵D₀ → ⁷F₁ (593 nm), ⁵D₀ → ⁷F₁ (599 nm), ⁵D₀ → ⁷F₂ (612 nm) and ⁵D₀ → ⁷F₂ (630 nm) energy levels transitions of Eu³⁺ ions, and the predominant emission peak was located at 612 nm. Compared with CoFe₂O₄/Y₂O₃:Eu³⁺ composite nanofibers, CoFe₂O₄@Y₂O₃:Eu³⁺ magnetic–fluorescent bifunctional coaxial nanofibers simultaneously provided higher magnetism and fluorescent intensity. The color, photoluminescent intensity and magnetism of the coaxial nanofibers can be tuned via adjusting the diversity and content of fluorescent compounds and the content of magnetic compounds. Formation mechanism of CoFe₂O₄@Y₂O₃:Eu³⁺ coaxial nanofibers was also presented. The bifunctional magnetic–photoluminescent CoFe₂O₄@Y₂O₃:Eu³⁺ coaxial nanofibers have potential applications in many fields due to their excellent magnetism and fluorescence.     

Janus nanofiber: a new strategy to achieve simultaneous enhanced magnetic-photoluminescent bifunction

Magnetic-photoluminescent bifunctional Janus nanofibers have been successfully fabricated by electrospinning technology using a homemade parallel spinneret. NaYF₄:Eu³⁺ and Fe₃O₄ nanoparticles (NPs) were respectively incorporated into polyvinyl pyrrolidone (PVP) and eleactrospun into Janus nanofibers with NaYF₄:Eu³⁺/PVP as one strand nanofiber and Fe₃O₄/PVP as another strand nanofiber. The morphologies, structures, magnetic and photoluminescent properties of the as-prepared samples were investigated in detail by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, vibrating sample magnetometry and fluorescence spectroscopy. The results show Janus nanofibers simultaneously possess superior magnetic and luminescent properties due to their special structure, and the luminescent characteristics and saturation magnetizations of the Janus nanofibers can be tuned by adding various amounts of NaYF₄:Eu³⁺ NPs and Fe₃O₄ NPs. Compared with Fe₃O₄/NaYF₄:Eu³⁺/PVP composite nanofibers, the magnetic-photoluminescent bifunctional Janus nanofibers provide better performances due to isolating NaYF₄:Eu³⁺ NPs from Fe₃O₄ NPs. The novel magnetic-photoluminescent bifunctional Janus nanofibers have potential applications in the fields of new nano-bio-label materials, drug target delivery materials and future nanodevices owing to their excellent magnetic and luminescent performance. More importantly, the design conception and construction technology are of universal significance to fabricate other bifunctional Janus nanofibers.     

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.     

Flexible special-structured Janus nanofiber synchronously endued with tunable trifunctionality of enhanced photoluminescence,electrical conductivity and superparamagnetism

We report a facile and highly-effective method to assemble luminescent–magnetic–electrical tri-functionalities into the special-structured Janus nanofibers. Novel and brand-new flexible special-structured [coaxial nanocable]//[nanofiber] Janus nanofibers synchronously endued with tuned and enhanced luminescent–magnetic–electrical trifunctionality have been prepared via electrospinning technology using a homemade coaxis//monoaxis spinneret for the first time. Each special-structured Janus nanofiber consists of a coaxial nanocable made of Fe₃O₄/PVP core and Eu(BA)₃phen/PVP shell as a half side with luminescent–magnetic bifunctionality and polyaniline (PANI)/PVP nanofiber as the other half side with electrically conductive functionality. The special and novel Janus nanofiber not only can guarantee effective separation of Fe₃O₄ nanoparticles (NPs) and PANI from rare earth complex, but also ensure the continuity of PANI in the matrix. It is satisfactorily found that the luminescent intensity of the novel special-structured Janus nanofibers respectively reaches up to 10 and 22 times higher than those of counterpart conventional [nanofiber]//[nanofiber] Janus nanofibers and composite nanofibers owing to its peculiar nanostructure. Compared with the counterpart conventional Janus nanofibers of two independent partitions, coaxial nanocable is used as one side of the special-structured Janus nanofiber instead of nanofiber, and three independent partitions are successfully realized in the special-structured Janus nanofiber, thus the interferences among various functions are further reduced, leading to the fact that more excellent multifunctionalities can be obtained. The novel Janus nanofibers possess excellent fluorescence, superparamagnetism and electric conductivity, and further, these performances can be respectively tunable via modulating the respective Eu(BA)₃phen, Fe₃O₄ and PANI contents. The design philosophy and the construction technique for the special-structured Janus nanofibers are of universal significance for the fabrication of other multifunctional Janus nanofiber of various performances.     

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.     

Parallel spinnerets electrospinning construct and properties of electrical-luminescent bifunctional bistrand-aligned nanobundles

A structure of electrical-luminescent bifunctional bistrand-aligned nanobundles has been successfully fabricated by specially designed parallel spinnerets electrospinning technology. Eu(BA)₃phen (BA = benzoic acid, phen = 1,10-phenanthroline) and polyaniline (PANI) were respectively incorporated into polyvinyl pyrrolidone (PVP) and electrospun into bistrand-aligned nanobundles with PANI/PVP as one strand nanofiber and Eu(BA)₃phen/PVP as another strand nanofiber. The morphologies and properties of the final products were investigated in detail by scanning electron microscopy, transmission electron microscopy, fluorescence spectroscopy, Hall effect measurement system, and UV–Vis-NIR spectrophotometer. It is found that the as-prepared samples exhibit the nanostructures of bistrand-aligned nanobundles. The mean diameter for individual nanofiber of the bistrand-aligned nanobundles is 180 nm. The [PANI/PVP]//[Eu(BA)₃phen/PVP] bistrand-aligned nanobundles possess excellent electrical conduction and luminescent properties. Fluorescence emission peaks of Eu³⁺ are observed in the [PANI/PVP]//[Eu(BA)₃phen/PVP] electrical-luminescent bifunctional bistrand-aligned nanobundles and assigned to ⁵D₀ → ⁷F₀ (581 nm), ⁵D₀ → ⁷F₁ (592 nm), ⁵D₀ → ⁷F₂ (615 nm) energy levels transitions of Eu³⁺ ions, and the ⁵D₀ → ⁷F₂ hypersensitive transition at 615 nm is the predominant emission peak. The electrical conductivity reaches up to the order of 10^?3 S/cm. The electrical conductivity and luminescent intensity of the bistrand-aligned nanobundles can be tunable by adding various amounts of PANI and rare earth complex. The novel [PANI/PVP]//[Eu(BA)₃phen/PVP] electrical-luminescent bifunctional bistrand-aligned nanobundles have potential applications in display devices and nanomechanics, etc. owing to their excellent electrical conduction and fluorescence.     

Electrospun Fe3O4/PVP//Tb(BA)3phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles

Fe₃O₄/PVP//Tb(BA)₃phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles based on Fe₃O₄ nanoparticles (NPs) and terbium complex Tb(BA)₃phen (BA = benzoic acid) were fabricated by employing a parallel axial electrospinning setup and were characterized by X-ray diffraction, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy, fluorescence spectroscopy, and vibrating sample magnetometer. It is found that Fe₃O₄ NPs were only dispersed into one strand of the bistrand aligned composite nanofibers bundles, but no nanoparticles in the other strand. And the average diameter of the individual strand fiber was 200 ± 25 nm. The bistrand aligned composite nanofibers bundles exhibit strong green emissions under the excitation of 275 nm ultraviolet light, and the ⁵ D ₄ → ⁷ F ₅ hypersensitive transition at 545 nm was the predominant emission peak of Tb³⁺ ions. The newly obtained bifunctional nanofibers bundles exhibit excellent magnetism and high fluorescence intensity and are expected to apply in biology cell separation, magnetic resonance imaging, drug deliver, and fluorescence immunoassays/imaging.     

A new strategy to assemble enhanced magnetic–photoluminescent bifunction into a flexible nanofiber

A new type of magnetic–photoluminescent bifunctional [Fe₃O₄@Y₂O₃:Eu³⁺]/polyvinyl pyrrolidone (PVP) flexible composite nanofibers were successfully prepared via electrospinning through dispersing Fe₃O₄@Y₂O₃:Eu³⁺ core–shell structured nanoparticles (NPs) into the PVP matrix. The structure, morphology, and properties of the flexible composite nanofibers were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and fluorescence spectroscopy. The diameter of [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers is ca. 128.57 ± 36.72 nm. Fluorescence emission peaks of Eu³⁺ in both Fe₃O₄@Y₂O₃:Eu³⁺ NPs and [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers are observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (533, 586, 592, 599 nm), ⁵D₀ → ⁷F₂ (612 nm), and ⁵D₀ → ⁷F₃ (629 nm) of Eu³⁺ ions. Compared with Fe₃O₄/Y₂O₃:Eu³⁺/PVP nanofibers, [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers possess much stronger luminescence. The as-prepared [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers simultaneously exhibit excellent magnetism and photoluminescent performance. The intensities of magnetism and luminescence of the composite nanofibers can be simultaneously tuned by adjusting the amount of Fe₃O₄@Y₂O₃:Eu³⁺ NPs introduced into the nanofibers. The high performance [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers have potential applications in bioimaging, cell separation, and future nanomechanics.     

Photoluminescence–electricity–magnetism trifunction simultaneously assembled into one flexible nanofiber

In order to develop new-typed multifunctional composite nanofibers, Eu(BA)₃phen/PANI/Fe₃O₄/PVP trifunctional composite nanofibers with photoluminescence, electricity and magnetism have been successfully fabricated via electrospinning technology. Polyvinyl pyrrolidone (PVP) is used as a matrix to construct composite nanofibers containing different amounts of Eu(BA)₃phen, polyaniline (PANI) and magnetite Fe₃O₄ nanoparticles (NPs). X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, fluorescence spectroscopy and Hall effect measurement system are used to characterize the morphology and properties of the obtained composite nanofibers. The results indicate that the trifunctional composite nanofibers possess excellent luminescent, electrical conductivity and magnetic properties. Fluorescence emission peaks of Eu³⁺ are observed in the Eu(BA)₃phen/PANI/Fe₃O₄/PVP photoluminescent-electrical-magnetism trifunctional composite nanofibers and assigned to the of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (593 nm) of Eu³⁺, and the ⁵D₀ → ⁷F₂ hypersensitive transition at 615 nm is the predominant emission peak. The electrical conductivity reaches up to the order of 10^?3 S/cm. The luminescent intensity, electrical conductivity and saturation magnetization of the composite nanofibers can be tunable by adding various amounts of Eu(BA)₃phen, PANI and Fe₃O₄ NPs. The multifunctional composite nanofibers are expected to possess many potential applications in areas such as electromagnetic interference shielding, microwave absorption, molecular electronics and biomedicine.     

Electrospinning fabrication of color-tunable flexible composite nanofibers containing lanthanide ions

A novel color-tunable PVP/[Tb(BA)₃phen+Eu(BA)₃phen] luminescent composite nanofibers had been fabricated by single axial electrospinning. The morphology and elements components of the as-prepared nanofibers were characterized by field emission scanning electron microscopy and energy dispersive spectroscopy. The luminescent properties were systematically investigated by photoluminescence spectroscopy. The obtained nanofibers had excellent fibrous morphology and smooth surface, and the average diameter was about 200 nm. The novel luminescent composite nanofibers exhibited the green, orange and red fluorescence emission peaks at 490, 545, 592 and 616 nm, which were ascribed to the ⁵D₄ → ⁷F₆ (490 nm) and ⁵D₄ → ⁷F₅ (545 nm) energy transitions of Tb³⁺ ions, and the ⁵D₀ → ⁷F₁ (592 nm), ⁵D₀ → ⁷F₂ (616 nm) transitions of Eu³⁺ ions, respectively. The emitting color of the luminescent composite nanofibers could be tuned by adjusting the mass ratio of terbium complexes and europium complexes in a wide color range of red-yellow-green under the excitation of 274-nm single-wavelength ultraviolet light. The color-tunable luminescent composite nanofibers have potential applications in the fields of display panels, lasers and bioimaging.     

Facile electrospinning fabrication and photoluminescence of LaOI:Tb3+ one-dimensional nanomaterials

LaOI:Tb³⁺ nanomaterials including nanofibers, nanobelts, and hollow nanofibers were successfully synthesized by electrospinning combined with a double-crucible iodination method using NH₄I as iodine source for the first time. X-ray diffractometry analysis revealed that LaOI:Tb³⁺ nanostructures were phase-pure tetragonal structure with space group of P4/nmm. Scanning electron microscopy analysis showed that the diameters of LaOI:Tb³⁺ nanofibers, hollow nanofibers and the width of nanobelts were respectively 199.5 ± 30, 376.05 ± 48 nm and 5.2 ± 1.3 μm under the 95 % confidence level. The thickness of the tubewall for hollow nanofibers was 40.5 nm and the thickness of LaOI:Tb³⁺ nanobelts was 154 nm. Photoluminescence (PL) study demonstrated that the LaOI:Tb³⁺ nanomaterials exhibited the emission peaks located at 485, 544, 583 and 625 nm, which were ascribed to ⁵D₃ → ⁷F₁, ₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄ and ⁵D₄ → ⁷F₃ of energy level transitions of Tb³⁺, respectively. The PL intensity was strongly affected by the Tb³⁺-doping concentration, and the optimum quenching concentration was 9 %. The luminescence intensity of LaOI:Tb³⁺ nanofibers was obviously stronger than that of LaOI:Tb³⁺ hollow nanofibers and nanobelts under the same measuring conditions. Commission Internationale de L’Eclairage (CIE) analysis demonstrated that the luminescence color of LaOI:9 % Tb³⁺ nanostructures were located in the green region in CIE chromaticity coordinates diagram. The possible formation mechanisms of LaOI:Tb³⁺ one dimensional nanomaterials were also proposed.     

Fabrication and luminescence properties of YF3:Eu3+ hollow nanofibers via coaxial electrospinning combined with fluorination technique

Polyvinyl pyrrolidone (PVP)–PVP/[Y(NO₃)₃ + Eu(NO₃)₃] core–sheath composite nanofibers were prepared by coaxial electrospinning, and then Y₂O₃:Eu³⁺ hollow nanofibers were synthesized by calcination of the as-prepared composite nanofibers. For the first time, YF₃:Eu³⁺ hollow nanofibers were successfully fabricated by fluorination of the Y₂O₃:Eu³⁺ hollow nanofibers via a double-crucible method using NH₄HF₂ as fluorinating agent. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM), and fluorescence spectrometer. YF₃:Eu³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 211 ± 29 nm. Fluorescence emission peaks of Eu³⁺ in the YF₃:Eu³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₁ (587 and 593 nm), ⁵D₀ → ⁷F₂ (615 and 620 nm), and the ⁵D₀ → ⁷F₁ hypersensitive transition at 593 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Eu³⁺ hollow nanofibers were located in the red region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Eu³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Eu³⁺ ions and reached a maximum at 7 mol% of Eu³⁺. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.     

Study on terbium doped lanthanum oxybromide luminescent nanoribbons and nanofibers

Terbium doped lanthanum oxybromide (LaOBr:Tb³⁺) nanoribbons and nanofibers were successfully synthesized by double-crucible bromination of the electrospinning-derived La₂O₃:Tb³⁺ nanoribbons and nanofibers using NH₄Br powders as the bromine source. The structure and morphology of the samples were investigated by X-ray diffractometry and scanning electron microscopy. The results indicated that LaOBr:Tb³⁺ nanoribbons and nanofibers were pure tetragonal in structure with space group of P4/nmm. The width of LaOBr:Tb³⁺ nanoribbons were 2.33 ± 0.33 μm and the diameter of LaOBr:Tb³⁺ nanofibers was 90.08 ± 15.19 nm. The photoluminescent properties of LaOBr:Tb³⁺ nanoribbons and nanofibers were also characterized systematically. Under the excitation of 253-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emission of predominant peak at 543 nm. The optimum doping molar concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanoribbons is 5 %. Interestingly, the luminescence intensity of LaOBr:5 %Tb³⁺ nanofibers is obviously greater than that of LaOBr:5 %Tb³⁺ nanoribbons under the same measuring conditions. Moreover, the luminescence colors of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The mechanism of double-crucible bromination method was also proposed. This new bromination technique not only can inherit the morphology of rare earth oxides precursor, but also can be used to fabricate pure-phase rare earth oxybromide at low temperature compared with conventional high temperature solid state bromination reaction method. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

Green photoluminescence and afterglow of Tb-doped SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

Trivalent terbium-doped strontium aluminate (SrAl₂O₄:Tb³⁺) nanoparticles were synthesized via the sol–gel combustion technique, and the green photoluminescence (PL) and afterglow were evaluated to clarify the afterglow mechanism of SrAl₂O₄:Tb³⁺. The green PL of SrAl₂O₄:Tb³⁺ with characteristic emissions at 488, 543, 586, and 622 nm indicated that Tb dopant acts as the luminescent center of the PL. Contrarily, the green afterglow of SrAl₂O₄:Tb³⁺ was a broadband spectrum with its peak centered at around 520 nm, but no traces of Eu were found in SrAl₂O₄:Tb³⁺ phosphors within the detection limit of 1 μg/g. The band structures and density of states of SrAl₂O₄:Tb³⁺ were calculated within the framework of density functional theory. Both the ground state of Tb³⁺ dopant and the trap levels of oxygen vacancy were quantitatively determined in the band gap of SrAl₂O₄. Our results suggest that the deep electron trap of oxygen vacancy in the host acts as the luminescent center of the green afterglow from SrAl₂O₄:Tb³⁺. A possible afterglow mechanism is proposed to shed fresh light on the green afterglow of SrAl₂O₄:Tb³⁺.     

Electrospinning preparation of LaOBr:Tb3+ nanostructures and their photoluminescence properties

Tb³⁺-doped LaOBr nanostructures including nanofibers, nanobelts, and hollow nanofibers were synthesized for the first time via calcinating the electrospun polyvinyl pyrrolidone/[La(NO₃)₃ + Tb(NO₃)₃ + NH₄Br] composites. X-ray diffraction analysis revealed that LaOBr:Tb³⁺ nanostructures are tetragonal in structure with space group of P4/nmm. The morphologies and sizes of LaOBr:Tb³⁺ nanostructures were investigated using scanning electron microscope and transmission electron microscope. Under the excitation of 254-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emissions of predominant peak at 543 nm, which is ascribed to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. It is found that the optimum doping concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanofibers is 3 %. Interestingly, we found that the luminescence intensity of hollow nanofibers is obviously greater than that of nanofibers and nanobelts for LaOBr:Tb³⁺ under the same measuring conditions. Moreover, the luminescence of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The formation mechanisms of LaOBr:Tb³⁺ nanofibers, nanobelts, and hollow nanofibers were also proposed. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

A single flexible nanofiber to obtain simultaneous tunable color-electricity bifunctionality

For the purpose of developing new-typed multifunctional composite nanofibers, novel composite nanofibers with tunable color-electricity bifunctionality have been successfully fabricated via facile one-pot electrospinning technology. The obtained bifunctional composite nanofibers are composed of polyvinyl pyrrolidone (PVP) as the matrix, Tb(BA)₃phen and Eu(BA)₃phen (BA = benzoic acid, phen = phenanthroline) as luminescence materials and polyaniline (PANI) as conductive material. Scanning electron microscopy, energy dispersive spectrometry, fluorescence spectroscopy and Hall effect measurement system are used to characterize the morphology structure and properties of the [Tb(BA)₃phen + Eu(BA)₃phen]/PANI/PVP composite nanofibers. The results indicate that the bifunctional composite nanofibers possess excellent photo luminescence and electrical conduction. The emitting color of the luminescent composite nanofibers can be tuned by adjusting the mass ratios of Tb(BA)₃phen, Eu(BA)₃phen and PANI in a wide color range of red-yellow-green under the excitation of 297-nm single-wavelength ultraviolet light. The electrical conductivity reaches up to the order of 10^?4 S/cm. The luminescent intensity and electrical conductivity of the composite nanofibers can be tunable by adding various amounts of Tb(BA)₃phen, Eu(BA)₃phen and PANI. The bifunctional composite nanofibers are expected to possess many potential applications in areas such as color display, electromagnetic shielding, molecular electronics and biomedicine.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Study of CoFe2O4 Particles Synthesized with Various Concentrations of PVP Polymer

CoFe₂O₄ particles were synthesized using metallic nitrates and polyvinylpyrolidone (PVP) using sol–gel method followed by calcination for 2 h at 960 °C. PVP performed as a surfactant and the effect of various concentrations of PVP on the resultant CoFe₂O₄ powder was studied. The resultant samples were characterized by XRD, TG/DSC, HR-SEM and VSM. X-ray diffraction results indicated the crystalline phase of CoFe₂O₄ particles and impurity phase of hematite was observed for higher PVP concentrations. SEM images demonstrated the influence of PVP concentration on the size of the particles. By VSM measurements, the variations in magnetic properties with respect to PVP concentration are studied. All the magnetic characteristics H _c , M _s and M _r increased for 6 wt% and 15 wt% of PVP concentration. The CoFe₂O₄ particles synthesized with the optimum concentration of PVP may be very attractive for potential applications because of their outstanding magnetic properties (M _s =81.1 Am²/kg, H _c =831 Gauss).     

Luminescent electrospun composite nanofibers of [Eu(TFI)3(Phen)]·CHCl3/polyvinylpyrrolidone

The luminescent europium complex [Eu(TFI)₃(Phen)]·CHCl₃ (TFI = 2-(2,2,2-trifluoroethyl)-1-indone, Phen = 1,10-phenanthroline) was incorporated into poly(vinylpyrrolidone) (PVP) matrixes and electrospun into nanofibers. The effect of [Eu(TFI)₃(Phen)]·CHCl₃ on the morphology and luminescence of composite nanofibers has been studied. FT-IR and TGA analyses of the composite nanofibers have been conducted and discussed. Further, the Judd–Ofelt theory is employed to study the effect of the dispersion of [Eu(TFI)₃(Phen)]·CHCl₃ and the interactions between the [Eu(TFI)₃(Phen)]·CHCl₃ molecules and neighboring chain segments of PVP. The results suggest that PVP led to the increased polarization degree of Eu³⁺ ions and significantly enhanced the electronic dipole-allowed transitions of Eu³⁺ ions, resulting in the enhancement of luminescent efficiency.