Search

Europium-doped gadolinium carbonates particles have been prepared via urea-assisted precipitation. The reaction has been followed step by step with the investigations of the precipitate by transmission electron microscopy and wide-angle X-ray scattering, in relation with infrared absorption and thermal analyses. It has been observed that spherical particles of (Gd0.95Eu0.05)(OH)CO3, monodispersed in size and amorphous, precipitate first and then transform to agglomerated platelike crystals of (Gd0.95Eu0.05)2(CO3)3·2H2O as the precipitation continues. The Eu3+5D0→ 7FJemission spectrum and the 5D0lifetime in the two carbonate matrices have been measured. Selected hydroxycarbonate nanoparticles (NPs), with diameters of 164 ± 20 nm, have been then transformed to oxide NPs having the cubic crystalline structure C-(Gd0.95Eu0.05)2O3, with the same shape and size. The photoluminescence (PL) properties of hydroxycarbonate and oxide NPs, and of their colloidal suspensions in water, have been investigated. The hydroxycarbonate and the oxide NPs exhibit same PL intensities when excitation is achieved in one of the Eu3+(4f6) levels. Tests of in vitro fluorescence imaging have been performed. The luminescent NPs have been observed after their internalization by human cervical carcinoma (HeLa) cells. It is concluded that the controlled (urea-assisted) precipitation is appropriate to synthesize Gd(OH)CO3:Eu3+and Gd2O3:Eu3+nanoparticles having adequate characteristics for biolabeling.

In this study, we investigated the influence of ZnO particles obtained by spray pyrolysis with submicron dimensions on the structure, morphology, thermal stability, photodegradation stability, mechanical and antibacterial properties of isotactic polypropylene (iPP)/ZnO composites prepared by melt mixing. The results of the morphological analyses indicate that, despite the surface polarity mismatch between iPP and ZnO, the extrusion process and the unique characteristics of the utilized particles allow a composite with a fair distribution of particles to be obtained, although some agglomeration phenomena can occur, which primarily depends on the composition of the composite. The addition of ZnO particles imparts significant improvements on the photodegradation resistance of iPP to ultraviolet irradiation, which confirms that ZnO particles act as screens for this type of radiation. The thermal stability of the iPP/ZnO composites is improved with respect to that of neat iPP and increases with the content of ZnO. The iPP/ZnO composites exhibit significant antibacterial activity against Escherichia coli. This activity is dependent on exposure time and composition.

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 ± 3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3inside the core of uniform silica nanoparticles (40 ± 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen.

Bi2O3films have been deposited on alumina particles by Fluidized Bed Chemical Vapor Deposition at atmospheric pressure, using bismuth triphenyl and oxygen as precursors. In the operating range tested, the presence of Bi on the whole particles has been evidenced by EDX, and the existence of the α and γ phases of Bi2O3has been revealed consistently by Raman spectroscopy and by XRD.

Borate phosphors, with formulations Y0.95Eu0.05BO3(YBEu), Y0.95Tb0.05BO3(YBTb), Y0.57Gd0.38Eu0.05BO3(Y6G4BEu), and Y0.57Gd0.38Tb0.05BO3(Y6G4BTb) have been synthesized by spray pyrolysis at the maximum temperature of 700 °C, and then annealed at 1200 °C. The yttrium oxide-doped phosphor Y0.95Eu0.05O1.5(YOEu) was obtained by the same experimental conditions. The UV−VUV excitation spectra of the samples were recorded using synchrotron radiation. The emission intensities of these phosphors have also been investigated as a function of plasma gas pressure in a dedicated experimental setup. The intensities in the emission spectra were integrated, to compare the relative efficiencies of the phosphors. All phosphors were more efficient with increasing gas pressure in the plasma chamber. The emission intensity of YOEu was similar to that of YBEu or Y6G4BEu at low Ne−Xe pressure, but stronger at high pressure. For both lanthanide activators, the mixed borates Y6G4B and the pure YBO3(YB) have about same luminescence efficiency at low pressure, but the Y6G4B are better matrices than YB at high Ne−Xe pressure. With the introduction of Gd3+in the borates, the emission intensity is enhanced due to a better spectral overlap with the plasma emission at 173 nm, and also the occurrence of multiple energy transfers between Gd3+ions before transfer to the emitter Eu3+or Tb3+. A “color effect” with the variation of pressure in the plasma chamber is observed for the Eu3+-doped phosphors. The orange:red intensity ratio (i.e., 5D0→ 7F0,1(560−600 nm)/5D0→ 7F2(600−640 nm)) increases as the gas pressure is raised. This observation is related to the spectral changes occurring in the plasma, and it is corroborated by the observation of selective excitation in the VUV range of Eu3+at Civersus C1crystallographic sites.

Luminescent colloidal nanosystems based on europium-doped biomimetic apatite were prepared and investigated. The colloids were synthesized by soft chemistry in the presence of a phospholipid moiety, 2-aminoethylphosphoric acid (AEP), with varying europium doping rates. Physicochemical features, including compositional, structural, morphological, and luminescence properties, were examined. Experimental evidence showed that suspensions prepared from an initial Eu/(Eu + Ca) molar ratio up to 2% consisted of single-phased biomimetic apatite nanocrystals covered with AEP molecules. The mean particle size was found to depend closely on the AEP content, enabling the production of apatite colloids with a controlled size down to ca. 30 nm. The colloids showed luminescence properties typical of europium-doped systems with narrow emission bands and long luminescence lifetimes of the order to the millisecond, and the data suggested the location of Eu3+ions in a common crystallographic environment for all the colloids. These systems, stable over time and capable of being excited in close-to-visible or visible light domains, may raise interest in the future in the field of medical imaging.

Yttrium orthorborate YBO3containing 0.5 or 5 atom % of Eu3+has been prepared by the spray-pyrolysis method. Low-temperature, high-resolution emission spectroscopy has been used to probe the local site symmetries of Eu3+ions accommodated on the Y3+sites in YBO3:Eu3+(0.5 atom %) and hence to determine the crystal structure of the title compound. The use of point group selection rules enabled a consistent spectral interpretation by envisaging distinct Ciand C1symmetry Eu3+sites, in accordance with the neutron diffraction study of Lin et al. (Chem. Mater.2004, 16, 2418). The assignment of features in the 10 K visible absorption spectrum of YBO3:Eu3+(5 atom %) is also consistent with the two-site model, but it was found that the site occupation by Eu3+differs from the expected ratio 2C1:1Ci. The fitting of 31 crystal-field levels of the C1site has been made with some approximations by employing 7 parameters. In addition, the emission spectrum of YBO3:Eu3+containing a trace amount of Y3BO6has been compared with those of YBO3:Eu3+and Y3BO6:Eu3+, which serves as a reference to elucidate the concern on the red/orange color ratio of YBO3:Eu3+emission.

Here, the large scale synthesis of nanocrystalline ZnO spheres and tetrapods in the size range of 8–40 nm by chemical vapor synthesis using zinc metal as precursor is described. A detailed study of the effect of experimental parameters on the morphology and yield is presented. High‐resolution transmission electron microscopy images of the tetrapods show that they are formed by the self assembly of four nanorods in the vapor phase. The tetrapods have optical absorption coefficients that are one order of magnitude greater than the spheres and show intense UV luminescence whereas the spheres show only the green emission. The observed differences in the optical properties are related to the presence of surface defects present in the nanospheres. The tetrapods have increased efficiencies for application in dye sensitized solar cells when compared to spheres.

An optical investigation of LiYO2doped with 2% Pr3+and 5% Tm3+is presented. The unit cell is monoclinic and the site symmetry at the rare earth site is C1. The absorption, excitation and fluorescence spectra at 20 K are utilized to determine the electronic structure of the ground 4f2and 4f12configurations respectively. For LiYO2:Pr3+, 64 energy levels from 3H4up to 3P2at 22 000 cm−1are reported. For LiYO2Tm−1, 58 energy levels from 3H6up to 3P2at 38 000 cm−1and the relative intensities for absorption from the 3H6ground state are given. A crystal field analysis of the data is performed. Configuration interaction is applied to LiYO2:Pr3+and improves the results. While Eu3+and Tb3+doped LiYO2are good red and green phosphors respectively, LiYO2:5%Tm3+luminesces only weakly. The reason for that is the existence of many possible paths for up-conversion processes.

During a study of the LaF3–ZrF4 system, both La3Zr4F25 and α-LaZr3F15 compounds have been evidenced. Their crystal structures have been determined from single-crystal X-ray diffraction data. La3Zr4F25 crystallises in the cubic system with a=12.384 Å and I4&cmb.macr;3d space group (no. 220). Its crystal structure is built up of (ZrF6)2– octahedra and (LaF8)5– dodecahedra sharing corners. The low temperature form, α , of LaZr3F15 is orthorhombic (space group Pmmn, no. 59) with a=15.721 Å, b=16.299 Å, c=8.438 Å. Its structure is built of corner-sharing tricaped trigonal prisms surrounding the La3+ ions and both octahedra and monocapped trigonal prisms encompassing the Zr4+ ions. This structure is characterised by dynamically disordered (ZrF6)2– complex anions.The Eu3+ luminescence properties of these phases have been investigated and are discussed in relationship with their crystal structures.

The formation of the title particles by urea‐assisted precipitation from nitrate precursors in water at temperatures above 60 °C is monitored by TEM, wide‐angle X‐ray scattering, and IR spectroscopy.

For the application of nanocrystalline ZnO in pharmaceuticals and cosmetics, in addition to high purity, a precise control of particle size, shape and agglomeration is necessary so that transparent films with high absorption coefficients can be obtained. In this communication we report the synthesis and structure-property correlation of ZnO nanospheres and tetrapods prepared by the gas phase oxidation of zinc metal precursor. We have evaluated the ecotoxicity of the ZnO tetrapods and spheres by studying the rate of formation of reactive oxygen species using EPR spectroscopy. We find that ZnO tetrapods form reactive oxygen species, but at a rate much lower than nanocrystalline TiO2 when irradiated with UV-A

Chemical vapor synthesis is a convenient one‐step synthesis process for the production of nanocrystalline powders. On page 875, Bacsa et al. report that by controlled variation of experimental parameters, tetrapods (as in image) or spherical ZnO nanocrystals can be selectively obtained directly from Zn metal precursor. Shape control leads to improved optical properties and a better performance when applied as electrodes in dye sensitized solar cells.