Zhenling Wang

Down- and up-conversion photoluminescence, cathodoluminescence and paramagnetic properties of NaGdF4 : Yb3+,Er3+ submicron disks assembled from primary nanocrystals

NaGdF4 : Yb3+,Er3+ submicron disks have been synthesized at a relatively low temperature in aqueous solution with citric acid as the structure-directing agent. The structure, luminescence, and magnetic properties of the synthesized materials have been characterized by a variety of techniques. The as-prepared NaGdF4 : Yb3+,Er3+ has hexagonal structure, and is mainly composed of submicron disks with a diameter of around 870 nm and a thickness of about 420 nm. Citrate groups selectively bonded to a certain crystal surface of the nanocrystals probably provide the driving force that makes primary particles assemble into submicron disks. The phase structure of these submicron disks is affected by the annealing temperature, while the disk morphology could be essentially preserved even when annealed at high temperatures. The annealed submicron disks exhibit prominent visible emission with different excitation sources, including ultraviolet light, low-voltage electron beam and near-infrared laser. In addition, these disks exhibit paramagnetic features with the mass magnetic susceptibility value of 9.82 × 10−5 emu/g·Oe at room temperature. These multifunctional disks would have potential in applications as building blocks for many functional devices such as solid-state lasers, lighting and displays, magnetic resonance imaging and so on.

Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln=Eu3+,Ce3+,Tb3+) spherical particles

Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to D50→F71 and D50→F72 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.

A strategy for simultaneously realizing the cubic-to-hexagonal phase transition and controlling the small size of NaYF4:Yb3+,Er3+ nanocrystals for in vitro cell imaging

Hexagonal-phase NaYF(4):Yb(3+),Er(3+) up-conversion nanocrystals (UCNCs) are synthesized by a combination of refluxing and hydrothermal treatment. This strategy leads to only a slight increase in particle size, from 4.5 to ca. 10 nm, during the cubic-to-hexagonal phase transition. The hexagonal UCNCs can be internalized by HeLa cells and exhibit visible emission in the cells under near-infrared excitation.

Hybrid luminescence materials assembled by [Ln(DPA)3](3-) and mesoporous host through ion-pairing interactions with high quantum efficiencies and long lifetimes.

A kind of mesoporous hybrid luminescence material was assembled through the ion exchange method between [Ln(DPA)3]3− and ionic liquid functionalized SBA-15. [Ln(DPA)3]3− was successfully anchored onto positive-charge modified SBA-15 by the strong electrostatic interaction. In [Ln(DPA)3]3−, Ln3+ ions are in 9-fold coordination through six oxygen atoms of carboxyl groups and three nitrogen atoms of pyridine units, leaving no coordination site for water molecules. Therefore the hybrids possess prominent luminescent properties, SBA-15-IMI-Tb(DPA)3 and SBA-15-IMI-Eu(DPA)3 exhibit high quantum yield values of 63% and 79%, and long lifetimes values of 2.38 ms and 2.34 ms, respectively. Especially, SBA-15-IMI-Eu(DPA)3 presents a high color purity, and the red/orange intensity ratio is as high as 7.6. The excellent luminescence properties and ordered mesoporous structures give rise to many potential applications in optical and electronic areas.

Multi-color luminescence of uniform CdWO4 nanorods through Eu3+ ion doping

Uniform Eu3+ doped CdWO4 nanorods were prepared via a simple hydrothermal method and characterized by X-ray diffraction, transmission electron microscopy, photoluminescence (PL) spectroscopy and PL lifetime measurements. The results indicate that the obtained Eu3+ doped CdWO4 nanorods have monoclinic phase structure, and the phase structure can be retained at Eu3+ doping concentrations of 0.4–4.0%. The diameter of nanorods decreases from 27 to 15 nm with an increase in the doping concentrations, and the morphology becomes irregular at the Eu3+ doping concentration of 6.5%. Under the excitation of ultraviolet light, the relative intensities of blue-green emission ascribed to WO42− and red emission from Eu3+ can be tuned through doping Eu3+ ions into the CdWO4 nanorods and thus altering the energy transfer between WO42− and Eu3+. Hence, the multi-color luminescence in the same host at a single excited wavelength can be realized simply by altering the doping concentration of Eu3+. These luminescent nanomaterials may have potential applications in displays, light sources, bio-imaging and so on.

Water-soluble Tb3+ and Eu3+ complexes based on task-specific ionic liquid ligands and their application in luminescent poly(vinyl alcohol) films

Novel water-soluble lanthanide complexes (Ln(IMI-DPA)3) have been synthesized using the task-specific ionic liquid consisting of a dipicolinic acid motif as the sensitizer of lanthanide luminescence. In Ln(IMI-DPA)3, Ln(3+) ions are in 9-fold coordination through six carboxylate oxygen atoms and three nitrogen atoms in pyridine units, and the water molecule is excluded from the coordination sphere of the lanthanides. It is found that Ln(IMI-DPA)3 possess bright luminescence, long luminescence lifetime in aqueous solution, high thermal stability and good water solubility. Furthermore, these complexes can be incorporated into water-soluble poly(vinyl alcohol) (PVA) matrixes to obtain highly luminescent, transparent and flexible PVA composite films. The emission colors of the films can be tuned from red, orange, yellow, light green, green to white light by regulating the concentration of the various luminescent components.

Controllable synthesis and formation mechanism of luminescent monodispersed NaEuF4 submicron disks through assembled nanocrystals

Monodispersed NaEuF4 submicron disks assembled from nanocrystals exhibit prominent red emission under the excitation of UV light, low-voltage electron beam, and commercial blue light-emitting diode. These disks would have potential applications in solid-state lighting, field emission displays, etc.

Blue-Green, Red, and White Light Emission of ZnWO4-based Phosphors for Low-Voltage Cathodoluminescence Applications

ZnWO 4 and ZnWO 4 :Eu 3+ particles were prepared by refluxing in water solution using polyethylene glycol as a capping agent and then annealed at different temperatures. The samples were characterized by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, and cathodoluminescence spectra. The as-prepared amorphous samples annealed at high temperature (500-700°C) are sanmartinite structure of ZnWO 4 , and the spherical morphologies are basically retained, except for the increase of the particles size (from 28 to 56 nm). The low-voltage luminescent properties of these tungstate phosphors can be tuned by the doping of Eu 3+ ions and annealing treatment. ZnWO 4 and ZnWO 4 :Eu 3+ particles annealed at 500°C or above exhibit strong blue-green and white light emission under the excitation of low-voltage electron beams, respectively, the former originating from the intrinsic WO 6- 6 complex, and the latter due to the combination of the emissions arising from the intrinsic WO 6- 6 and doped Eu 3+ ions. The as-prepared ZnWO 4 :Eu 3+ particles only emit a red light resulting from the 5 D 0 → 7 F J (J = 1, 2, 3, 4) transitions of Eu 3+ ions.

Highly luminescent hydrogels synthesized by covalent grafting of lanthanide complexes onto PNIPAM via one-pot free radical polymerization

Highly luminescent PNIPAM–Ln(DPA)3 hydrogels have been synthesized by one-pot free radical polymerization in aqueous systems at room temperature. We firstly synthesized a bifunctional chelating ligand named as 4-vinylpyridine-2,6-dicarboxylic acid (4-VDPA), which contains two different moieties: (1) a pyridine-2,6-dicarboxylic acid (DPA) moiety that can sensitize the luminescence of Tb3+ and Eu3+ and (2) a reaction functional group that can be polymerized by free radical initiation. Therefore, the luminescent lanthanide complexes can be grafted onto the hydrogel matrix via one-pot free radical polymerization of [Ln(4-VDPA)3]3−, N-isopropylacrylamide (NIPAM) and N,N′-methylenebis(2-propenamide) (MBA). The results indicated that the final hydrogels possess bright luminescence, long luminescence lifetimes and high quantum efficiency. Moreover, the emission colors of the hydrogels can be tuned from red, reddish orange, orange-yellow, yellow, and green by varying the molar ratio of added Eu3+ to Tb3+.

Construction of pH-responsive and up-conversion luminescent NaYF4:Yb3+/Er3+@SiO2@PMAA nanocomposite for colon targeted drug delivery

Colon-targeted drug delivery system has attracted much interest because it can improve therapeutic efficacy and reduce the side effect in practical clinic. Herein, we constructed a multifunctional drug delivery system with colonic targeting and tracking by up-conversion (UC) luminescence based on core-shell structured NaYF4:Yb3+/Er3+@SiO2@PMAA nanocomposite. The resultant materials exhibited bright UC luminescence, pH-responsive property and excellent biocompatibility. The drug release behaviors in different pH environment were investigated using 5-aminosalicylic acid (5-ASA) as a model drug. The 5-ASA molecules release from NaYF4:Yb3+/Er3+@SiO2@PMAA nanocomposite exhibit a significant pH-responsive colon targeted property, i.e., a little amount of drug release in simulated gastric fluid (SGF, pH = 1.2) but a large amount of drug release in simulated colonic fluid (SCF, pH = 7.4) Moreover, the drug release process could be monitored by the change of UC emission intensity. These results implied that the multifunctional nanocomposite is a promising drug carrier for targeted release of 5-ASA in the colon.