Photoluminescence Studies on ZnO Thin Films Obtained by Sol-Gel Method

The sol-gel process is a friendly room temperature method to prepare transparent glasses in the form of monoliths, films, and fibers. The zinc oxide films have been obtained by sol-gel method, which are very important materials in the ceramic technology due to their piezoelectric properties and applications in various pressure transducers and acoustic-optic devices, surface and bulk acoustic wave devices, and solar cells. Structure and characteristic ultraviolet-blue emissions of amorphous and crystalline zinc oxide thin films–coated glass substrates by dip-coating deposition are explained by photoluminescence studies in this chapter

Sol-Gel Method - Design and Synthesis of New Materials with Interesting Physical, Chemical and Biological Properties

The sol-gel method is a powerful route of synthesis used worldwide. It produces bulk, nano- and mesostructured sol-gel materials, which can encapsulate metallic and magnetic nanoparticles, non-linear azochromophores, perovskites, organic dyes, biological molecules, etc.. This can have interesting applications for catalysis, photocatalysis; drug delivery for treatment of neurodegenerative diseases such as cancer, Parkinson's and Azheimer's. In this book, valuable contributions related to novel materials synthesized by the sol-gel route are provided. The effect of the sol-gel method to synthesize these materials with potential properties is described, and how the variation of the parameters during the synthesis influences their design and allows to adjust their properties according to the desired application is discussed

Photostability of laser dyes incorporated in Formamide SiO2 ORMOSILs

The sol–gel process provides a low temperature chemical route for the preparation of rigid transparent matrix materials. Under this process, luminescent organic dye molecules were incorporated into organically modified silicate (ORMOSIL) host matrices. The photostability of these laser dyes encapsulated in a solid matrix was studied using optical absorption and luminescence. The photochemical mechanisms of the dye response under N2 laser irradiation were studied using UV and fluorescence spectra measurement. The evolution of the maximum of the emission and excitation curves as function of accumulated irradiated energy was fitted by exponential equations. The matrix protects the dye from the oxidation and dimerization reactions. The dye molecules exhibited photobleaching due to their photodegradation. The ORMOSIL doped with Nile blue exhibits good photostability after 6 h of irradiation

Seminarios virtuales sobre Materiales Avanzados

El seminario estará a cargo de la Dra. Ma. Guadalupe Valverde Aguilar http://www.fciencias.unam.mx/... y versará sobre Estudio de las propiedades ópticas y eléctricas en nanomateriales sol-gel de SiO2 y TiO2. Este se llevará a cabo de forma presencial en el Auditorio Alejandra Jáidar del Instituto de Física de la UNAM el jueves 29 de abril a las 12 hrs tiempo de la ciudad de México.Estudio de las propiedades ópticas y eléctricas en nanomateriales sol-gel de SiO2 y TiO2Composite PCTV 100e 2010-04-29 09-58-04h.mpg/fl

Eu3+ as optical probe of the structure in amorphous and nanocrystalline TiO2 films prepared by sol-gel method

In this work the Eu3+ ion was used as optical probe, by considering its hypersensitive transitions to follow changes in the local environment. Eu3+ ions were incorporated into gel via dissolution of soluble species into the initial precursor TiO2 sol. The TiO2/Eu3+ films were spin-coated on glass wafers. A spectroscopic study of the Eu3+ impurity in function of the heat treatment provided to the TiO2 matrix was done. Anatase nanophase was obtained after heat treatment at 600°C for 1h and it was detected by X-ray diffraction. An absorption band located in the UV region between 300-360 nm is due to the band gap of the titania host. Results of emission and excitation spectra at room temperature of Eu3+ inserted in the TiO2 matrix are presented. The ratio of the 7F2/7F1 transitions was calculated. The evolution of this ratio was interpreted in terms of the Eu3+ symmetry site change when the nanocrystalline TiO2 phase was obtained

Fotoconductividad en películas sol-gel de ZnO-TiO2

En este trabajo se incluye la síntesis, caracterización y el estudio de fotoconductividad de películas delgadas amorfas y nanocristalinas de ZnO-TiO2. Estas películas fueron depositadas sobre sustratos de vidrio por el método de spin-coating. Las películas fueron caracterizadas por difracción de rayos X, absorción óptica, espectroscopia infrarroja y microscopía electrónica de barrido. Las películas nanocristalinas sinterizadas a 520 ºC por una hora muestran la fase anatasa. Los resultados experimentales de fotoconductividad fueron ajustados con líneas rectas tanto para la oscuridad como bajo iluminación a 310, 439 y 633 nm. Esto indica un comportamiento óhmico. Los parámetros fotovoltaico y fotoconductivo fueron ajustados por el método de mínimos cuadrados con líneas rectas para las películas nanocristalinas, y con curvas polinomiales para las películas amorfas

Silver core-silver oxide shell nanoparticles embedded in mesostructured silica films

Metallic silver particles in the nanometer size range were obtained in SiO2 matrix by the reduction of AgNO3 with the non-ionic diblock copolymer (Brij 58). Hexagonal mesostructured solgel films were synthesized by dip-coating method using the surfactant Brij58 to produce channels into the film, which house the silver nanoparticles. Optical properties of the metallic nanoparticles were studied by UV-Vis spectroscopy, TEM and HRTEM images. The experimental absorption spectrum of the metallic silver nanoparticles exhibits an absorption band located at 438 nm and a shoulder at longer wavelength. The TEM images show randomly distributed silver nanoparticles (Type I) along with some oriented as long line (Type II). Both distributions exhibit a silver oxide shell around of them. The second shell covering the silver core - silver oxide shell system is related to the surfactant. The optical absorption spectrum was modelled using the Gans theory. The fit shows two main contributions related to metallic silver nanoparticles with different axial ratios, and surrounding of a dielectric medium with high refractive index. Presence of the high refractive index silver oxide shell was confirmed by X-ray diffraction technique. The contributions of silver core and silver oxide shell play important roles in the optical properties of the films

Orientational dynamics of DR1 molecules in sol-gel films

A physical model for the induced orientation of azochromophores in sol–gel films is presented. This model describes the poling time dependence of the order parameter based on a damped oscillator. This model provides a different approach to the chromophore orientational dynamics, with the property that all its parameters are physical meaningful. The model results have been experimentally verified in DR1 doped sol–gel films, by means of optical absorption measurements. We considered two kinds of sol–gel films: amorphous with a side-chain doping and mesostructured ones with a guest–host doping. The experimental results were fitted successfully with our model