Aurelia Meghea

Influence of Roughness Surfaces on Third-Order Nonlinear-Optical Properties of Erbium-Doped Zinc Oxide Thin Films

ABSTRACT Zinc oxide (ZnO) and erbium-doped zinc oxide (ZnO:Er) thin films were deposited on heated glass substrates using the spray pyrolysis technique. Third-order nonlinear-optical properties of the thin films have been investigated using the third harmonic generation (THG) at wavelength of 1064 nm in picosecond regime. The dependence of third-order nonlinear susceptibility and transmission characteristics on the thin films roughness has been evaluated. Third-order nonlinear optical susceptibility (χ(3)) values of the studied materials were in the remarkable range of 10−2 esu. The morphologic properties of the deposited films have been analyzed using x-ray diffraction (XRD) and atomic force microscopy (AFM) and the luminescence properties by cathodoluminescence (CL). A correlation between optical properties and structural properties is given.

Effects of Prooxidants on Human Serum Exposed to 50 Hz Magnetic Fields

The purpose of this article is to evaluate magnetic field effects (50 Hz, different magnetic intensities) on the chemiluminescence intensity of human serum. We find that 1 and 2 h of exposure increased the chemiluminescence emission. The addition to the serum of prooxidants FeCl2 and H2O2 in different concentrations increased the chemiluminescence intensity even more.

New optical materials based on natural extracts immobilized in different silica polymeric matrices

This study aims at investigating the effect of grape seed extract (GSE) immobilization into individual pores and cages of silica/silsesquioxane networks. It might be considered that, since chemically stable guest molecules are already present in the precursor solution for the synthesis, the entrapping of vegetable extract proceeds without significant modification or other adverse changes during the synthesis. As a consequence, some organic chromophore contained in grape seed extract with enhanced optical functions such as fluorescence and nonlinear optical properties can be perfectly incorporated and preserved into the silica based materials. The grape seed extract was immobilized into inorganic and hybrid silica-silsesquioxane matrices by the sol-gel method and it has been proved to be present as an integral part within the matrices pores and with a uniform size distribution. The fluorescence spectrum was discussed in terms of the effect of the host-guest interaction on these properties, and as a function of template type (glucidic and nonionic template). The formation of GSE doped glassy silica materials was investigated and demonstrated by extensive characterization through UV-VIS and FT-IR spectroscopy, estimation method of polymeric aggregates size (DLS), atomic force microscopy (AFM), and optical properties (by fluorescence and non-linear optical measurements). The results of this study demonstrate that GSE entrapped in inorganic and hybrid polymer networks have promising potential as optical systems, due to the extensive conjugation of polyphenolic mixture from the extract and the protective and optical properties of silica polymers.

Encapsulating the green tea extract by templated sol-gel procedure based on nonionic tensioactive agent of alkenyl succinic anhydrides class

The sol-gel method has been proved to be a suitable approach for the introduction of some sensitive organic substances into inorganic matrices. By extension of bioencapsulation sol-gel method, this article is focused on encapsulation of green tea extract (GTE) in some silica polymeric matrices. Green tea has been extensively used for medical purposes, as promising antioxidant, anti-inflammatory and anti-carcinogenic agents, investigated particularly in the chemoprevention and treatment of skin photodamage. Green tea extract exhibits high content of polyphenols (bioflavonoids), being a rich source of epigalocatehin galat (EGCG) that is over 200 times more potent than vitamin E as scavenger of free radicals and pro-oxidants. The chemical instability of tea polyphenols (TP) can be a major drawback for many applications (e.g. medical application). This has opened the possibility of using a hybrid host network in order to preserve their structural properties. By isolating of organic polyphenol molecules into individual pores and cages of some silica polymers prepared by a templated sol-gel process may confer an appropriate stability for this purpose. In this study the GTE was successfully encapsulated in two inorganic silica and hybrid silica-silsesquioxane polymers, by addition of vegetable extract into a silica precursor solution templated with a nonionic tensioactive agent of vegetal origin (from high oleic sunflower oil), belonging to alkenyl succinic anhydrides class. Experimental studies of the antioxidant stability and fluorescence properties of GTE encapsulated in silica and silica-silsesquioxane polymers are also discussed. Spectral changes observed by UV-VIS-NIR and FT-IR spectroscopy, increased antioxidant activity (after UV-A and UV-B irradiation) tested by chemiluminescence assays and enhanced fluorescence properties by fluorescence measurements and also less aggregation, by DLS and TEM techniques, were observed in encapsulated samples, in contrast with that of native GTE.