National Institute Of Materials Physics - Romania

Photoluminescence (PL) spectra recorded at room temperature (RT) in polycrystalline BaFCI:Eu2+ X-ray storage phosphor have shown the europium associated luminescences, a broad luminescence band at 385nm (3.22eV) with a 3.3 +/- 0.1 mu s PL lifetime accompanied by a luminescence line at about 368nm (3.37eV). The energy difference Delta EB-L =226cm(-1) between the two excited levels from which the europium associated band and line luminescences took place was computed. An additional broad luminescence band at about 425nm (2.92eV) with 0.7 +/- 0.1 mu s PL lifetime has been attributed to the europium luminescence perturbed by an impurity. Time resolved spectroscopy measurements have shown that no other impurity luminescences (like oxygen-vacancy centres) can be observed at RT except the europium associated ones.

In order to be used for medical applications, a material must exhibit many specific characteristics, of which the most fundamental is related to biocompatibility. Lately, the iron oxide nanoparticles are preferred for biomedical applications because they present a superparamagnetic behaviour at room temperature. The preparation method and conditions of iron oxide nanoparticles represents some of the most important challenges that will determine the particle size and shape, the size distribution, the surface chemistry of the particles and consequently their magnetic properties. The samples were characterized by X-ray diffractions (XRD), transmission electron microscopy (TEM) and infrared spectroscopy.

This paper presents a study of the thermal regime associated with the experimental configuration used for the growth of doped organic crystals from the melt in Bridgman-Stockbarger configurations. For different systems, host: metadinitrobenzene (m-DNB), benzil/guest: m-DNB, naphthalene, iodine, I have investigated the effect of the changes in the experimental conditions (dopant type and concentration, c=0.5-3 wt %, thermal gradient at the growth interface, Delta T=6-33 degrees C, moving speed of the solid-liquid interface, V=0.7-2.7 mm/h) on the crystals growth process. I have made comparisons between the particularities of the incorporation mechanism of the big acceptor (atom:iodine c=0.5; 1; 2 wt %; molecule: m-DNB and naphthalene c=1.5; 3 wt %) and clopant segregation mechanism, and the transmission properties of different monocomponent crystalline organic matrix (m-DNB and benzil). I have also investigated the influence of the simultaneous presence of two dopants (m-DNB or naphthalene/iodine) in organic benzil matrix and their effect on the optical properties. have evaluated the growth interface stability in our Bridgman-Stockbarger experimental configuration and analysed the conditions for the generation of the morphological instabilities in benzil-dopant system.

The iron oxide-based nanomaterials have a great importance because of their impact on a wide number of industries. They have many properties and applications in domains as: environmental protection, biomedical, catalysis, information displays and electronics. In order to avoid the tendency of nanoparticles to aggregate, they are often included in sol-gel derived silica matrices, thus being also ensured a homogeneous dispersion of the ultra-fine metal oxide particles in the host matrix. The reasons of the attempt are both an economic and a non-pollutant one, tacking into account the fact that it is well known that aqueous silica sol is cheaper and less toxic than TEOS. The Fe3O4 was introduced in the reaction mixture as aqueous suspension. A final iron content related to SiO2 of 3% wt. was chosen for the prepared nanocomposite. Thermal analysis, IR spectroscopy, XRD and TEM methods have been used for the structural characterisation,. Some experiments of water depollution (from As) have been proceeded using the prepared Fe3O4-SiO2 nanocomposite.

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

Sandwich type (MIS) heterostructures based on layers of organic semiconductors as meta-dinitrobenzene (m-DNB) and perylene or perylene derivative 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) have been prepared using alternative methods (rapid thermal directional solidification or two-steps, vacuum evaporation and deposition process) on different substrates (single crystal silicon wafer and textolite covered with copper film). Subsequently indium, gallium, aluminium of high purity (5N) and silver have been used for the preparations of the metallic contacts. This paper presents some investigations of the contact between different organic semiconductors and several metals: meta-dinitrobenzene/Cu, perylene/In, peryiene/Al, perylene/Ga, perylene/Ag, PTCDA/AI, PTCDA/Ga, and PTCDA/Ag. The comparative study of the electrical conduction properties of these organic semi conductor/metal contacts has emphasised significant differences depending on the metal type, metal/organic semiconductor interface properties and quality of the contact, which is determined by the preparation method (pressing, melting, vacuum evaporation, painting) and selected contact cinfiguration. The experimental data obtained using the 2 points contact geometry have evidenced linear or power IN dependences of the investigated metallic contacts emphasising the importance of the space-charge phenomenon and defects on the charge carriers' transport in these structures.

Porous membranes containing cylindrical pores with diameters ranging from a few tens of nanometers to a few tens of micrometers were prepared by using the ion track technique. Swift heavy ions (e.g. Au with 11.4 MeV/nucleon specific energy) were used for creating the ion tracks in polycarbonate foils. Etching was performed using an aqueous solution of NaOH containing methanol. The growth of the alkali-halides micro- and nanorods was performed by evaporation from a saturated solution. The rods were imaged using scanning electron microscopy. The method opens up the possibility of growing nanostructures with applications as nanolaser media or nanoscintillators.

We used the template method to prepare CdTe wires with diameters ranging from 80 nm to 1 mu m. As templates we used polycarbonate and polyethilene tereplitalate ion track membranes and as the method of filling the pores of such membranes we employed electrochemical deposition. The conditions (i.e. bath composition and deposition potential) necessary to obtain the stoichiometric composition of the semiconductor were found. Scanning and transmission electron microscopy were employed for morphological characterization of the nano and microwires. Energy dispersive X-ray analysis was employed for determining the Cd/Te ratio. Selected area electron diffraction was employed for structural measurements. Reflection spectroscopy measurements were performed on nanowire arrays for determining the band gap of the deposited nanostructures. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Manganese and copper doped ZnO films and nanowire arrays were prepared by cathodic electrodeposition from aqueous solution. The electrochemical process was examined by linear voltammetry and the morphology and the composition of obtained semiconductor were observed by SEM and EDX measurements. Optical absorption spectra indicated the presence of copper in ZnO: Mn: Cu nanowire arrays as Cu2+ ions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report in this contribution on the photosensitization effect of ZnO nanostructured thin films with copper-phthalocyanine (CuPc). ZnO films were prepared by pulsed laser deposition (PLD), on optical glass substrates, covered with 300 nm thick ITO films. The structure and morphology of ZnO films were optimized for photovoltaic-cell applications by controlling the growing conditions. ZnO films (wurtzite type) were (001) preferentially oriented in the growth direction. Organic dyes were vacuum sublimated on ZnO films, and subsequently a 300 nm thick copper film was vacuum sublimated on top of the structure, acting as an ohmic contact. Action spectra of ITO/ZnO/CuPc/Cu photovoltaic structures were recorded and a well defined response was observed in the range of absorption bands of organic dyes. The dark IN characteristics were also recorded, and electrical characterizations of the photovoltaic structures are given. The measured fourth quadrant IN characteristics under integral illumination (photoelement regime), allowed us to extract the typical photovoltaic cells parameters.