National Institute Of Materials Physics - Romania

We synthesized by wet chemical route a novel europium-potassium phthalate complex Eu3+K+[(COO)(2)(C6H4)](2). The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium-potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the D-5(0) -> F-7(J) (J = 1-4) Eu (III) ion's transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded. (c) 2012 Elsevier B.V. All rights reserved.

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.

Styrene, methyl methacrylate and glycidyl methacrylate vinyl monomers were grafted onto chitosan by surfactant-free emulsion copolymerization using potassium persulfate as initiator. The grafted compounds were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential measurements. X-ray diffraction showed changes in the crystallinity pattern of chitosan after the copolymerization reaction. Evidence of grafting was confirmed by FTIR spectroscopy. From zeta potential measurements it is found that the surfaces of graft copolymers latex particles have positive charges resulting from the cationic chitosan molecules. The morphology evaluated by SEM, TEM and AFM proves that in the absence of chitosan, latexes of vinyl homopolymers contain quasi-monodispersed spheres with average diameter of about 400 nm or 250 nm while the graft copolymers latexes are formed by clustered irregular beads with average diameter around 100 nm.

Given the evolution of imaging techniques in the biomedical field is becoming more necessary to develop sensitive markers, less toxic and not least more economical. Upconverting luminescent nanocrystals doped with rare earth ions, excited in infrared and emitting in visible, are considered real concurrent to classical fluorescent markers, featuring a number of advantages in rapport with them. The aim of this study is to prepare NaYF4 nanoparticles doped with erbium and ytterbium for biological applications in bioimaging techniques. After synthesis, upconverting nano particles were coated with SiO2 for surface sealing and passivation. The nano particles were characterized by X-ray diffraction, luminescence spectroscopy, electronic microscopy and dynamic light scattering. The interaction of the nanoparticles with mimicking cell membrane models was studied. NaYF4 nanoparticles showed a good size distribution and good emission efficiency. The uncoated nanoparticles increase the fluidity of the lipid monolayer, while the effect of the silica coated nanoparticles is substantially reduced.

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5 - 2.6 eV and a red luminescence at similar to 1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array. (C) 2012 Elsevier Ltd. All rights reserved.

Ag-doped nanocrystalline hydroxyapatite nanoparticles (Ag:HAp-NPs) (Ca10-x Ag (x) (PO4)(6)(OH)(2), x (Ag) = 0.05, 0.2, and 0.3) with antibacterial properties are of great interest in the development of new products. Coprecipitation method is a promising route for obtaining nanocrystalline Ag:HAp with antibacterial properties. X-ray diffraction identified HAp as an unique crystalline phase in each sample. The calculated lattice constants of a = b = 9.435 , c = 6.876 for x (Ag) = 0.05, a = b = 9.443 , c = 6.875 for x (Ag) = 0.2, and a = b = 9.445 , c = 6.877 for x (Ag) = 0.3 are in good agreement with the standard of a = b = 9.418 , c = 6.884 (space group P6(3)/m). The Fourier transform infrared and Raman spectra of the sintered HAp show the absorption bands characteristic to hydroxyapatite. The Ag:HAp nanoparticles are evaluated for their antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae, Providencia stuartii, Citrobacter freundii and Serratia marcescens. The results showed that the antibacterial activity of these materials, regardless of the sample types, was greatest against S. aureus, K. pneumoniae, P. stuartii, and C. freundii. The results of qualitative antibacterial tests revealed that the tested Ag:HAp-NPs had an important inhibitory activity on P. stuartii and C. freundii. The absorbance values measured at 490 nm of the P. stuartii and C. freundii in the presence of Ag:HAp-NPs decreased compared with those of organic solvent used (DMSO) for all the samples (x (Ag) = 0.05, 0.2, and 0.3). Antibacterial activity increased with the increase of x (Ag) in the samples. The Ag:HAp-NP concentration had little influence on the bacterial growth (P. stuartii).

ZnO films were electrodeposited from an aqueous nitrate bath on ITO/glass substrates. The process was performed not by the usual potentiostatic approach but by using potential ramps with different sweep rates. We tested these ramps in both directions i.e. either towards electronegative (direct) or electropositive (inverse) potential. As expected, the samples prepared in different deposition conditions show different morphology, different quality of crystalline structure and different optical properties. By employing inverse ramps we prepared films with high quality structural and optical properties. We assume that in these conditions the growth is followed by an etching process which preferentially removes the areas with high defect concentration and leads to the formation of hollow hexagonal prisms. (c) 2012 Elsevier B.V. All rights reserved.