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.     

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.     

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.     

Flexible Janus nanofiber to acquire tuned and enhanced simultaneous magnetism-luminescence bifunctionality

A novel nanostructure of [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] magnetic-luminescent bifunctional Janus nanofibers has been successfully fabricated via electrospinning technology using a homemade parallel spinneret. Electrospun YAG:7 % Tb³⁺ luminescent nanofibers and CoFe₂O₄ magnetic nanofibers were respectively incorporated into polyvinyl pyrrolidone (PVP) matrix and electrospun into Janus nanofibers with CoFe₂O₄ magnetic nanofibers/PVP as one strand nanofiber and YAG:7 % Tb³⁺ luminescent nanofibers/PVP as another strand nanofiber. [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] magnetic-luminescent bifunctional Janus nanofibers possess superior magnetic and luminescent properties due to their peculiar nanostructure, and the luminescent characteristics and saturation magnetizations of the Janus nanofibers can be tuned by adding various amounts of YAG:7 % Tb³⁺ luminescent nanofibers and CoFe₂O₄ magnetic nanofibers. Compared with CoFe₂O₄/YAG:7 % Tb³⁺/PVP composite nanofibers, the magnetic-luminescent bifunctional Janus nanofibers provide higher performances due to isolating YAG:7 %Tb³⁺ luminescent nanofibers from CoFe₂O₄ magnetic nanofibers. Formation mechanism of [CoFe₂O₄/PVP]//[YAG:7 % Tb³⁺/PVP] Janus nanofibers is also presented. The design conception and construction technology are of universal significance to fabricate other bifunctional Janus nanofibers.     

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.     

Fabrication of Er3+-doped LaOCl nanostructures with upconversion and near-infrared luminescence performances

LaOCl:Er³⁺ nanofibers and nanobelts were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl powders as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Er³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameter of LaOCl:Er³⁺ nanofibers and the width of nanobelts respectively were 161.15 ± 18.11 nm and 6.11 ± 0.19 μm under the 95 % confidence level, and the thickness of nanobelts was 116 nm. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Er³⁺ nanostructures exhibited strong green and red UC emission centering at 525, 548 and 671 nm, respectively attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_l5/2 energy levels transitions of Er³⁺ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the changing of concentration of Er³⁺ ions, and the optimum molar percentage of Er³⁺/(La³⁺+Er³⁺) ions was 5 % in the LaOCl:Er³⁺ nanostructures. The LaOCl:x %Er³⁺ nanobelts have higher UC emission (both red and green) intensity than the counterpart nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Er³⁺ nanostructures were achieved under the excitation of a 532-nm laser. Commission Internationale de L’Eclairage analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Er³⁺ ions, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism of LaOCl:Er³⁺ nanostructures were also proposed.     

Synthesis and luminescence properties of Yb3+–Er3+ co-doped LaOCl nanostructures

LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Yb³⁺, Er³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameters of LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers, respectively, were 117.87 ± 15.48 and 141.09 ± 17.10 nm under the 95 % confidence level. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Yb³⁺, Er³⁺ nanostructures exhibited strong green and red UC emission centering at 526, 548, and 671 nm, respectively, attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_l5/2 transitions of Er³⁺ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the addition of Yb³⁺ ions, and the optimized molar ratio of Yb³⁺ to Er³⁺ was 10:1 in the as-prepared nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Yb³⁺, Er³⁺ nanostructures were achieved under the excitation of a 532-nm laser. CIE analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Yb³⁺ (and/or Er³⁺) ions and morphologies of nanomaterials, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism and the formation mechanisms of LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers were also proposed.     

The structure and luminescence characteristics of LaOBr: Tb<Superscript>3+</Superscript>(Dy<Superscript>3+</Superscript>)

The rare earth luminescence materials LaOBr:Tb³⁺(Dy³⁺) were synthesized at high temperature (HT) and treated by high pressure (HP), and the structure and luminescence characteristics of the samples were studied. The results show that the co-doping with Dy³⁺ may make the luminescence strength increase greatly and energy transfer takes place between Tb³⁺ and Dy³⁺ cations. The XRD results show that no obviously structural change occurs after the HP and HT treatment.     

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.     

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.     

SrWO4:Tb3+ nanoparticles: synthesis,characterization, and luminescence

Nanoparticles of SrWO₄ doped with Tb³⁺ were synthesized in ethylene glycol, Dimethyl sulfoxide, and water. X-ray powder diffractions show that the nanoparticles synthesized in all these solvents have a pure tetragonal scheelite structure without the presence of deleterious phases. Scanning electron microscopy images show that nanoparticles are in the range of 15–25 nm with an inhomogeneous nature. The emission spectra of SrWO₄:xTb³⁺ nanoparticles show the characteristic green emission (545 nm) of Tb³⁺ ions corresponding to ⁵D₄ → ⁷F₅ transition due to efficient charge transfer from WO₄ ^2? to Tb³⁺ ions, when they are excited at 254 nm. Other emissions can be observed due to ⁵D₄ → ⁷F_{6, 4, 3} transitions. The optimum concentration of Tb³⁺ ions for the highest luminescence was found to be 10 mol%. The luminescence intensity of the samples prepared in ethylene glycol is higher than that in Dimethyl sulfoxide and water. The excellent luminescence properties of SrWO₄:Tb³⁺ phosphor makes it as a potential green phosphor.     

Study of the relationship between crystal structure and luminescence in rare-earth-implanted Ga2O3 nanowires during annealing treatments

A systematical analysis of the correlation between the crystalline quality and the luminescence of rare-earth-implanted β-Ga₂O₃ nanostructures with potential applications in visible and ultraviolet photonics is presented. Europium ions led to red emission while gadolinium ions are efficient ultraviolet emitters. Different degrees of lattice recoveries of the nanostructures have been achieved after implantation by rapid thermal annealing treatments carried out at different temperatures. The recovery process has been analyzed by transmission electron microscopy (TEM), high-resolution TEM, and Raman techniques. High-fluence implantation with either of the two rare earth ions induces partial amorphization of the structures. Partial recrystallization of the nanostructures above 500 °C is revealed by Raman analysis. Nearly complete recovery of the crystal structure is obtained in the annealing temperature range 900–1100 °C, coincident with the expected value for bulk Ga₂O₃. Cathodoluminescence and photoluminescence allowed comparison of the Eu³⁺ and Gd³⁺ intraionic luminescence lines after annealing at different temperatures and their correlation with the crystallinity. It has been found that the width of the Eu³⁺ luminescence lines clearly correlates with the width of the Raman peaks, both decreasing with annealing temperature, which shows the possibility of using the luminescence of this rare earth as a probe for lattice disorder. On the other hand, our results suggest that Gd³⁺ lines are much less sensitive to disorder.     

Hydrothermal synthesis and luminescence of MWO4:Tb3+ (M = Ca,Sr, Ba) microsphere phosphors

Spherical MWO₄:Tb³⁺ (M = Ca, Sr, Ba) particles were synthesized by a hydrothermal route at 180 °C for 10 h. The synthesized MWO₄:Tb³⁺ particles were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and luminescence spectroscopy. The XRD and FT-IR results show that MWO₄:Tb³⁺ particles with a scheelite-type crystal structure were synthesized successfully. The SEM and TEM results show that uniform spherical particles in the range of hundreds of nanometers were obtained. The possible growth mechanism may be attributed to a typical Ostwald ripening process. The excitation spectra of MWO₄:Tb³⁺ phosphors show a strong absorption band of the WO₄ ^2? group and some weak absorption bands of Tb³⁺ ions. The emission spectra of MWO₄:Tb³⁺ phosphors show the characteristic emission bands of Tb³⁺ ions. CaWO₄:Tb³⁺ sample has the highest excitation and emission intensity.     

Photoluminescence properties of β-Ga2O3:Tb nanofibers prepared by electrospinning

One-dimensional Tb³⁺-doped β-Ga₂O₃ nanofibers were prepared by a simple and cost-effective electrospinning process. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman technique, and photoluminescence (PL) were used to characterize the electrospun nanofibers. FE-SEM results indicated that the diameters all of the nanofibers ranged from 100 to 300 nm, and the lengths of nanofibers reached up to several millimeters. The XRD and Raman results showed that the Ga₂O₃ phase belongs to the monoclinic phase. Under ultraviolet excitation, the β-Ga₂O₃:Tb³⁺ samples showed green emission with the strongest peak at 550 nm, corresponding to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The luminescence intensity had been further studied as a function of the doping concentration of Tb³⁺ in the β-Ga₂O₃ samples.     

Synthesis and Luminescence of BiPO4:Tb3+ Nanowires by a Hydrothermal Process

We synthesized BiPO₄:Tb³⁺ nanowires by the hydrothermal process. The synthesized nanoparticles were measured using XRD, SEM, and luminescence spectrophotometry. The XRD patterns and SEM images indicate that reaction time induces phase changes but has no obvious influence on size and morphology. All samples show characteristic excitation and emission bands of Tb³⁺ ions. The BiPO₄:Tb³⁺ samples reacted for 3.5 h showed the highest emission intensity, which was induced by the pure monoclinic phase.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

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.     

Improving photoelectrical performance of dye sensitized solar cells by doping Y2O3:Tb3+ nanorods

Y₂O₃:Tb³⁺ nanorods have been successfully synthesized via a hydrothermal method and then introduced into the photoanode of dye-sensitized solar cell. As a p-type dopant, Y₂O₃:Tb³⁺ enhances the Fermi level of TiO₂ film. Meanwhile, it also improves the short-circuit current density and the light-to-electric energy conversion efficiency by acting as a luminescence medium which can convert ultraviolet light to visible light efficiently. As a result, the conversion efficiency can reach 7.942 % when the doping amount is 4 wt%. The light-to-electric conversion efficiency is increased by a factor of 2.051 compared to that of a cell without Y₂O₃:Tb³⁺ doping. The mechanism has been discussed as well.     

Luminescence and structural properties of Y(Ta,Nb)O4:Eu3+,Tb3+ phosphors

Yttrium tantalate (YTaO₄), yttrium niobium-tantalate (YTaNbO₄) and yttrium niobate (YNbO₄) doubly doped by Eu³⁺ and Tb³⁺, were investigated using X-ray diffraction and X-ray excitation luminescence in order to study their structural and luminescent properties. By means of X-ray diffraction, the crystallographic data for YTaO₄ and YNbO₄ with double activation by Eu³⁺ and Tb³⁺ were first calculated. Under X-ray excitation luminescence, the rare earth emission centers contribute to the overall luminescence. Due to their various luminescence chromaticities, the proposed rare earth activated phosphors are promising materials for optoelectronics as well as for X-ray intensifying screens for medical diagnosis providing the broad variation of visible photoluminescence from blue to red.     

Facile synthesis of β-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals with down- and up-conversion luminescence

β-NaYF₄:Ln³⁺ (Ln = Eu, Tb, Yb/Er, Yb/Tm) hexagonal microrods have been successfully synthesized through a facile molten salt method without any surfactant. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. It is found that at a preferred reaction temperature of 400 °C, the structure of β-NaYF₄ can gradually transform from microtubes to microrods as reaction time extends from 0.5 to 4 h. Furthermore, as the molar ratio of NaF:RE³⁺ (RE represents the total amount of Y³⁺ and the doped rare earth elements such as Eu³⁺, Tb³⁺, Yb³⁺/Er³⁺, or Yb³⁺/Tm³⁺) increased, the phase of sample transforms from YF₃ into NaYF₄. Under the excitation of 395 nm ultraviolet light, β-NaYF₄:5 %Eu³⁺ shows the emission lines of Eu³⁺ corresponding to ⁵D_0-3 → ⁷F _J (J = 1–4) transitions from 400 to 700 nm, resulting in red down-conversion (DC) light emission. When doped with 5 % Tb³⁺ ions, the strong DC fluorescence corresponding to ⁵D₄ → ⁷F _J (J = 6, 5, 4, 3) transitions with ⁵D₄ → ⁷F _J (green emission at 544 nm) being the most prominent group that has been observed. Moreover, upon 980 nm laser diode excitation, the Yb³⁺/Er³⁺- and Yb³⁺,Tm³⁺- co-doped β-NaYF₄ samples exhibit bright yellow and blue upconversion (UC) luminescence, respectively, by two- or three-photon UC process. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.