National Institute Of Materials Physics - Romania

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860 articles found

731. Time-resolved luminescence spectroscopy of Eu2+ in BaFCl : Eu2+ X-ray storage phosphor

Authors: Secu, M; Secu, CE; Vasile, V; Predoi, D; Gazdaru, DM

Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1802, DOI:

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.

732. Characterisation of magnetic iron oxide in hydroxyapatite

Authors: Birsan, M; Predoi, D; Birsan, C; Secu, CE; Andronescu, F

Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1832, DOI:

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.

733. The colloidal route of the sol-gel process - an alternative to produce Fe3O4-SiO2 nanocomposites

Authors: Raileanu, M; Crisan, M; Ballo, A; Cosma, C; Petre, J; Stan, C; Predoi, D; Valsangiacom, CM; Tolea, F; Secu, C

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1402, DOI:

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.

734. Structural and magnetic properties of FexOy nanoparticles dispersed in silica matrix

Authors: Predoi, D; Clerac, R; Raileanu, M; Crisan, M; Zaharescu, M

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1498, DOI:

Some FexOy-SiO2 composites were prepared by the colloidal and alkoxidic route of the sol-gel method. The dried gels were thermally treated and the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorption (IR) spectroscopy, magnetic susceptibility measurements and Mossbauer spectroscopy. Nanoparticles of gamma and /or alpha iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the thermal treatment. It was observed that the particle sizes and the thermal stability of the iron oxide phases strongly depend on the preparation method. At temperatures above 400 degrees C, the gamma-phase begins to transform to the alpha-phase.

735. Preparation of metallic nanowires with magnetic properties using the template method

Authors: Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:

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.

736. Micro and nanorods of alkali halides grown in polymer templates

Authors: Enculescu, M; Enculescu, I; Sima, M; Neumann, R; Trautmann, C

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1563, DOI:

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.

737. Deposition and properties of CdTe nanowires prepared by template replication

Authors: Enculescu, I; Sima, M; Enculescu, M; Enache, M; Ion, L; Antohe, S; Neumann, R

Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1611, DOI: 10.1002/pssb.200675109

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.

738. ZnO : Mn : Cu nanowires prepared by template method

Authors: Sima, M; Enculescu, I; Sima, M; Enache, M; Vasile, E; Ansermet, JP

Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1527, DOI: 10.1002/pssb.200675126

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.

739. Photosensitization of ZnO nanostructured thin films with organic dyes

Authors: Tazlaoanu, C; Ion, L; Socol, G; Socol, M; Mihailescu, IN; Stanculescu, F; Enculescu, I; Ionescu, F; Magherusan, L; Antohe, S

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1346, DOI:

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.

740. Raman and photoluminescence studies on low-dimensional PbI2 particles embedded in polymer matrix

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1361, DOI:

Pbl(2) crystallite incorporated in optically transparent polyacrylamide and poly (vinyl alcohol) matrix have been studied by Raman scattering, photoluminescence (PL) at low temperature and Scanning Electron Microscopy (SEM). The small particles of Pbl(2) embedded in different host matrix were prepared by: i) cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide or poly (vinyl alcohol) and ii) by chemical reaction of KI and Pb(NO3)2 in aqueous polyacrylamide solution. In all cases, were identified hexagonal platelets of Pbl(2) and rods like particles. The rods are featured by a similar Raman spectrum and a specific green emission (cca 550 nm). Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the Pbl(2) layers of different molecular species. By compression the hybridized electronic level situated at the top of valence band, formed by the contribution.of the 6s and 5p states of Pb2+ and l ions, undergo a deformation that induces a weakness of the interaction between the lead ion and iodine electron within a layer so that the photoluminescence of intercalated Pbl(2) acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.