Ileana Rau

Influence of the silica based matrix on the formation of iron oxide nanoparticles in the Fe2O3–SiO2 system, obtained by sol–gel method

Composite iron oxide–SiO2 materials were prepared by a sol–gel method starting with two types of precursors, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS), as the SiO2 source. As the iron source a soluble Fe2+ salt, mainly Fe(SO4)2·7H2O, was used, the iron oxides were generated during the sol–gel process. The amorphous gels obtained were thermally treated up to 1000 °C in order to obtain iron oxides with different structures and grain size. The initial gels and the thermally treated samples were characterised by DTA/TGA analysis, DR-UV–VIS and IR-spectroscopy, EPR measurements, transmission electron microscopy (TEM) and BET surface area methods. The matrices obtained from the precursors play a major role in the evolution of the process. In both cases the initial gels are amorphous. In the non-porous matrix obtained by thermal treatment using methyltriethoxysilane (MTEOS), the tendency for crystallisation increases, and the iron oxide particle size is increased.

Biopolymer based system doped with nonlinear optical dye as a medium for amplified spontaneous emission and lasing

In this paper, we present results of detailed studies on amplified spontaneous emission (ASE) and lasing achieved in a double-layer system consisted of a biopolymer based matrix loaded with 3-(1,1-dicyanoethenyl1)-1phenyl-4,5dihydro-1H-pyrazole organic nonlinear optical dye and photochromic polymer. The laser action was achieved via distributed feedback configuration with third order of Bragg scattering on surface relief grating generated in photochromic polymer. To excite the luminescence, we have used 6 ns pulses of Nd:YAG laser at 532 nm. The ASE and lasing thresholds were estimated to be 17 mJ/cm2 and 11 mJ/cm2, respectively.

Comparison of Z-scan and THG derived nonlinear index of refraction in selected organic solvents

Nonlinear index of refraction of a series of organic solvents, measured by the nonlinear imaging (z-scan) technique, is compared with the same values derived from optical third-harmonic generation (THG). The systematic differences in the values obtained from the z-scan measurements and from THG are attributed to three factors: the value of the standard used in THG measurements, important rotational contribution in z-scan measurements, and the difference in dispersion for n2 derived from Kerr susceptibility and those derived from THG measurements. Using the recently proposed standard silica susceptibility value, one obtains a very good agreement for silica and significant differences for the solvents, particularly for CS2 and chlorobenzene. A correction based on a three-level model for centrosymmetric media is applied for dispersion.

Arsenic(V) Removal from Aqueous Solutions by Iron(III) Loaded Chelating Resin

A study of arsenic adsorption using iron(III) loaded chelating resin as adsorbent is presented. The experiments were carried out in batch mode by using aqueous solutions containing 1000 ppm As, and using an iron(III) loaded iminodiacetate resin (LEWATIT TP 207) with sorption capacity of 168 mg Fe/g resin. The equilibrium time for adsorption was found to be one hour under the experimental conditions used. The influence of pH was studied in the range of 0.8÷8.5. The highest arsenic adsorption was found at pH 1.7. Under these conditions the adsorption capacity for As was approximately 60 mg As/g resin.

Biopolymer Thin Films for Optoelectronics Applications

Nowadays one observes a growing interest in studying and application of “green materials” – biomaterials. For an appropriate use of them in practical devices a good knowledge and understanding of their properties are necessary. This paper presents some results obtained for two, the most abundant on the Earth, biopolymers which are DNA and collagen. In order to make these biopolymers useful they have to be functionalized with active molecules, bringing them a researched property. The biopolymers were doped with Rhodamine 590 and Disperse Red 1. The contact angle measurements are also presented and discussed. The present studies show that the properties of these materials depend on the dyes used to render them optically responsive in visible range and on the biopolymer as well. They show that interaction with substrate is modified by the added dye, as expected. We have measured also the optical damage threshold of studied biopolymers at 1,064 nm and we found that it is about one order of magnitude higher for the studied biopolymers as compared with the synthetic ones.

NANOCOMPOSITE MATERIALS FOR As(V) REMOVAL BY MAGNETICALLY INTENSIFIED ADSORPTION

New nanocomposite adsorbent based on silica and iron(III) oxide, thermally treated at 200°C has been used for the arsenic(V) removal. Adsorbents were prepared by sol–gel method, the iron oxides being generated in situ during the sol–gel process. Nanocomposite materials thus obtained have a convenient porosity and nanosized iron oxide content. The sorption experiments have been carried out in a batch mode by using aqueous solutions containing 1000 ppm As. The influence of different experimental parameters on the adsorption capacity was investigated. The effect of magnetic field on the enhancement of adsorption process was also revealed.

Optical Properties of Thin Films of DNA-CTMA and DNA-CTMA Doped with Nile Blue

Refractive index dispersion of thin films of deoxyribonucleic acid (DNA)-surfactant (CTMA) and doped DNA-CTMA-Nile Blue (NB) (5 w%) complexes are reported and discussed. The thermal variation of the thin film thickness was measured by ellipsometry. The DNA-CTMA complex exhibits a rarely observed negative thermal expansion between room temperature and ca. 85°C. Doping with NB decreases the temperature range of negative thermal expansion to between room temperature and ca. 70°C. The dopping by 5 w% of NB lowers the absolute value of negative thermal expansion of DNA-CTMA system from 5% to 2% within this temperature range.

Second–harmonic generation in poled polymers: pre–poling history paradigm

Experimental studies of second harmonic generation (SHG) from electric-field poled PMMA - DR1 system show occurrence of a maximum in diagonal and off diagonal tensor components χ(2)(-2ω;ω,ω) at 15 mol % concentration and a rapid decrease above, with a stabilization. The origin of the observed concentration dependence is studied using the Monte Carlo (MC) modeling. We find that presence of maximum is conditioned by the pre-poling history of the sample, when entanglement of linear dipolar structures takes place. Length of the pre-poling interval is an important kinetic parameter which differentiates between various nonexponential kinetics of build-up of polar phase responsible for strong/weak SHG susceptibility.

Enhancement of linear and nonlinear optical properties of deoxyribonucleic acid-silica thin films doped with rhodamine

In this work, we present the linear and nonlinear optical properties of DNA as functional material, incorporated into a silica material matrix with rhodamine organic dye. We observed that even low concentration of DNA affects the aggregate behavior of the dyes in silica films. The samples with DNA showed higher transmittance and fluorescence efficiency. Moreover, the presence of DNA has been found to significantly enhance the nonlinear optical response of the systems. In this way, we prove that silica materials can provide suitable matrices for hybridization with functional molecules and can be utilized as active optical waveguide materials with enhanced nonlinear optical properties.

Concentration Variation of Quadratic NLO Susceptibility in PMMA-DR1 Side Chain Polymer

Chemical synthesis and concentration dependence of two second order NLO tensor components: and was studied for a side chain polymer PMMA-DR1 in thin films by optical second harmonic generation techniques. The noncentrosymmetry was created by the corona poling technique. The results show that for small chromophore concentrations the susceptibility follows linearly the density number of active chromophores, reaches a maximum, than decreases and stabilizes.