Low-Temperature Anti-Stokes Luminescence in Zn1-xMgxSe Mixed Crystals

Investigations of photoluminescence and Raman scattering in the ternary Zn_1-xMg_xSe compounds at 4.2 K were performed both in the Stokes and anti-Stokes regions using cw laser excitation with various wavelengths within the transparency band of the crystals. The anti-Stokes luminescence was observed for the first time in the ternary Zn_1-xMg_xSe compounds. We have found variations in the shape and position of the Stokes and anti-Stokes luminescence bands with an increase in the band gap energy, which depends on magnesium content. We assume that the anti-Stokes emission is generated by two-step excitation via deep-level centers. It is shown that the low-temperature anti-Stokes photoluminescence can probe the spatial distribution profiles of impurities in the bulk of crystals.     

ZnS:Mn nanoparticles conjugated to sol–gel-derived silica matrices

Composites from ZnS:Mn nanoparticles and modified silicas are of interest for a broad range of potential applications in the form of films, structured particles, and self-assembled structures (e.g., colloidal crystals). They combine the versatility of silica sol gel chemistry with the wealth of functionalities available from doped nanoparticulate semiconductors (e.g., optical, electrical, and magnetic). In this work, ZnS:Mn nanoparticles have been prepared and modified in such a way that they can be incorporated seamlessly, either by inclusion or by covalent bonding into silicas. Functionalization was achieved through the use of silanes or thioles. Further processing by standard sol gel chemistry then either led directly to covalent conjugation with the silica network formed after condensation, or to isolated particles encapsulated in a silica shell. The results are heavily loaded (up to 30 wt%), transparent (including semiconductor particles that are smaller than 15 nm) and luminescent films, and massive bodies. In this work, the progress of nanocomposite formation was followed mainly by luminescence spectroscopy. Further work will have to address the electrical and magnetic properties of these nanocomposites as well.     

Influence of ZnO,SiO2 and TiO2 on the aging process of PLA fibers produced by electrospinning method

Journal of Thermal Analysis and Calorimetry - The aim of this work was to study the effect of ceramics particles addition (SiO2, ZnO, TiO2) on the ultraviolet (UV) aging of poly(lactic acid)...     

Preparation of luminescent ZnS:Cu nanoparticles for the functionalization of transparent acrylate polymers

Highly luminescent ZnS:Cu nanoparticles were synthesized in a coprecipitation route using aqueous salt solutions and thiopropionic acid as stabilizer. The method yields a stable, transparent particle dispersion in water and allows for a good control over particle size in the range of 3-10 nm as determined by dynamic light scattering, small angle X-ray scattering and transmission electron microscopy. Strong luminescence of the nanoparticles was observed under UV-excitation and emission colors could be adjusted in the range of blue to green by varying the Cu-doping concentration. The phase transfer of the ZnS:Cu nanoparticles into non-polar solvents using octylamine was used for a hydrophobic surface functionalization. The hydrophobic particles were used for the fabrication of transparent bulk nanocomposites via in situ-polymerization of dispersions in laurylacrylate. A high transparency of the composite materials, and the luminescence of the ZnS:Cu nanoparticles is retained during the phase transfer and the polymerization process allowing for the integration of a new luminescent functionality into the polymer material.     

Carbon and secondary deuterium kinetic isotope effects on SN2 methyl transfer reactions

Carbon and secondary deuterium kinetic isotope effect (KIE) for three types of S_N2 methyl transfer reactions have been predicted theoretically at a DFT level in gas phase and in aqueous solution modelled by the PCM continuum solvent model. No correlation between these isotope effects and geometrical features of the corresponding transition states (TSs), force constants of the imaginary frequency or Gibbs free energies of the studied reactions has been found. These findings suggest that comparative analysis of the magnitudes of the studied KIEs should be constrained to interpretation of the TS localization on the reaction coordinate only in a series of very closely related reactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Silica/lignosulfonate hybrid materials: Preparation and characterization

The research reported here concerns the synthesis, characterization and potential applications of silica/lignosulfonate hybrid materials. Three types of silica were used (Aerosil®200, Syloid®244 and hydrated silica), along with magnesium lignosulfonate. The effectiveness of the hybrid material synthesis methodology was confirmed indirectly, using Fourier transform infrared spectroscopy, elemental and colorimetric analysis. Dispersive-morphological analysis indicates that the products with the best properties were obtained using 10 parts by weight of magnesium lignosulfonate per 100 parts of Syloid®244 silica. The relatively high thermal stability recorded for the majority of the synthesized products indicates the potential use of this kind of a material as a polymer filler. Results indicating the high electrokinetic stability of the materials are also of great importance. Additionally, the very good porous structure properties indicate the potential use of silica/lignosulfonate systems as biosorbents of hazardous metal ions and harmful organic compounds.