We report the observation of the photorefractive effect in an organic−inorganic polymer composite photosensitized with nanosized cadmium sulfide particles, the surface of which is passivated utilizing p-thiocresol. The semiconductor nanoparticles are dispersed in a poly(N-vinylcarbazole) (PVK) polymer matrix that also acts as the charge-transport species. The ability of these particles to behave as the photosensitizer in a PVK matrix has been characterized through a dc photoconductivity experiment. In addition, for the photorefractive experiments, the second-order optically nonlinear chromophore 4-nitrophenyl-l-prolinol is also doped into the PVK matrix to elicit electro-optic response. Tricresyl phosphate is used to lower the glass-transition temperature of the material, allowing for room temperature in situ poling of the sample. In addition to the electric field dependence of the degenerate four-wave mixing diffraction efficiency, the photorefractive nature of the grating is confirmed via two-wave mixing asymmetric energy transfer. The paper also discusses briefly the methods employed in the syntheses of the capped CdS nanoparticles used in this study, which include the reverse micelle approach as well as competitive reaction chemistry. The resulting particles have been characterized using UV−vis absorption and X-ray diffraction.

We report the preparation, luminescent properties, and bioimaging applications of a novel zinc sulfide (core)-two-photon dye−silica (shell) multilayered heterostructure. The method utilizes reverse micelles synthesis involving multistep reactions as a result of which composite nanoparticles having different sizes and morphology can be obtained. The size of these composite nanoparticles is typically 15−30 nm. An increase in the luminescence intensity (∼70 times higher) and in fluorescence lifetime is observed for the dye encapsulated within the silica nanobubble. Photobleaching results indicate that the dye is truly encapsulated and the silica shell provides a barrier to penetration of oxygen, thereby making the dye more photostable. The application of these particles as nanoprobes for bioimaging of cells using two-photon laser scanning microscopy is also presented.

No abstract

We describe the synthesis and characterization of ultrafine TiO2 particles (in both anatase as well as rutile form) produced by a chemical reaction within the aqueous core of a water-in-oil microemulsion. The microemulsion was stabilized and the Ti4+ ions provided by a functionalized surfactant derived from the commercially available Aerosol-OT, i.e., sodium bis (2-ethylhexyl) sulfosuccinate (Na-DEHSS). The Na+ ions in Aerosol-OT were completely replaced by Ti4+ through an ion-exchange reaction in nonaqueous solvents. Ultrafine TiO2 particles were produced by the hydrolysis of the Ti-containing surfactant in the water droplets. The dependence of the size of the precipitated TiO2 · xH2O particles on various structure parameters of the microemulsion was studied in detail.

No abstract