Gadolinium oxide films, prepared by the sol-gel process, present waveguiding properties. Their structures were studied by waveguide Raman spectroscopy (WRS) and confirmed using transmission electron microscopy (TEM). The structural evolution of the layers with annealing temperatures from 650 up to 900 degreesC was investigated. The WRS results and TEM observations were correlated and revealed that crystallization started at 650 degreesC into the cubic phase. The mean diameter of the crystallites dispersed in the amorphous phase is around 5 nm at this temperature. The film is totally crystallized into the cubic phase at 700 degreesC. The monoclinic phase simultaneously appears at 800 'C and both phases still co-exist after heat treatment at 900 degreesC. The films present a heterogeneous structure at 900 degreesC with grain sizes varying from 5 up to 50 nm and as consequence their waveguiding properties strongly decrease. Copyright (C) 2003 John Wiley Sons, Ltd.

Recently, there has been a growth of interest in the preparation of new phosphor films for high-resolution X-ray imaging systems. Europium activated gadolinium oxide is very interesting because of its scintillation properties especially as a red component. The sol–gel method has been used to synthesize europium-doped gadolinium oxide films. The films present waveguiding properties and this special feature is used to study their microstructure by Raman spectroscopy in waveguiding configuration. Structural results, confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations, show that the crystallization in the cubic phase occurs at 700 °C. Opto-geometrical parameters were determined with respect to the annealing temperature. After annealing at 1000 °C, very dense europium-doped gadolinium oxide films are obtained with a thickness of 390 nm and a refractive index of 1.88 at 632.8 nm. Spectroscopic results constituted by emission spectra (UV and X-ray excitation) and decay measurements are presented.

Pure and Eu3+ ions doped YBO3 waveguide thin films were dip-coated for the first time through sol–gel route. The quality of the film depends significantly on the dip-coating conditions, especially on environment humidity. We succeeded to prepare crack free thick films with 16 layers and thickness of about 850 nm. It is found that the coating process obeys a two-step kinetics. The films were characterized by different methods, such as m-line spectroscopy, X-ray diffraction, electron microscopy and waveguide fluorescence spectroscopy (WFS). When the annealing temperature is lower than 600°C the film is amorphous and has good waveguide performance. The attenuation of the propagation we have reached is about 0.5 dB/cm. The film starts to crystallize at 700°C. The waveguide performance of the film decreases dramatically with the annealing temperature above 700°C. The result of WFS also indicates that this new kind of thin film is a good host material for active dopants. Our preliminary results show that the new thin film is of great potential for future application in optoelectronics.

In this paper we present results on CdS nanocrystal (NC) formation in ZrO2 thin film grown by sol–gel process. Raman and waveguiding Raman scattering spectroscopies were applied to determine CdS nanocrystal precipitation in our films. RBS (Rutherford back scattering) and optical absorption spectroscopy were applied to determine CdS distribution homogeneity through the layer depth, NC size and dispersion. Thus we obtained low size dispersed CdS nanocrystals with preparation temperature controlled size. Moreover, Raman and high-resolution transmission electron microscopy (HRTEM) evidenced simultaneous correlated crystallisation of hexagonal CdS and tetragonal/monoclinic ZrO2 phases. We applied also light induced dynamic grating technique under high excitation conditions in order to analyse dynamic properties of nonequilibrium charge carriers in thin films.

Very thin TiO2 films have been prepared by sol–gel and deposited on a silver layer for Surface Plasmon Resonance (SPR) measurements. Densification of the samples has been studied by determining from SPR measurements the optical index (ranging from 1.68 to 1.92) and thickness (ranging from 6 to 2 nm) at each step of the annealing procedure. The structure of the layer (amorphous and/or crystalline) has been checked at the final stage of the thermal treatment by High Resolution Transmission Electron Microscopy (HRTEM).

Er3+ doped ZrO2 thin films (1 mol%) are prepared by sol–gel process and dip-coating technique. After annealing the films exhibit good optical quality and waveguiding properties. The observed fluorescence of Er3+ ions, especially at 1.53 μm, is used by Waveguide Fluorescence Spectroscopy (WFS). It is shown that the band shape of the 4I13/2 → 4I15/2 transition depends on the annealing temperature. Waveguide Raman Spectroscopy (WRS) is used at room temperature in order to analyse the films structure. Such study was conducted for different annealing temperatures at an excitation wavelength where erbium absorption is low (i.e. 676.4 nm). An amorphous waveguide is obtained below 400°C. Up to 800°C, the tetragonal phase mainly appears, although both monoclinic and tetragonal phases are simultaneously detected in undoped waveguides at this temperature. High Resolution Transmission Electron Microscopy (HRTEM) observations provide the mean diameter of ZrO2 crystallites which increases up to 15 nm after a 800°C heat-treatment. This large size explains in part the high attenuation measured on this film at 676.4 nm (around 20 dB/cm).

We report on the preparation of SiO2 (20%)–TiO2 (80%) planar waveguiding layers by dip-coating technique. The layers are formed from originally prepared sol with the added CdO and the subsequent precipitation of CdS nanocrystals (NC) during H2S treatment. The initial sol doping up to 92 wt.% was reached. The determination of the refractive index and thickness of waveguiding layer by m-line spectroscopy is presented. The porosity of film is evaluated. Influence of carbon contamination of the layer's pre-surface area on the waveguiding properties is discussed. The possibilities of surface relief gratings as efficient input and output light couplers are demonstrated.

We report on the implementation of a two-grating coupler technique for measurement of repopulation of deep traps in CdS nanocrystallites embedded in a (Si0.2Ti0.8)O2 waveguiding glass layer of high refractive index. A sol–gel process is used to produce this waveguide. The low attenuation (∼1 dB/cm) of the waveguide allows to in- and out-couple light by surface relief gratings embossed on the top layer of the waveguide. The spectral region of waveguiding (≈700 nm) that was studied corresponds to the deep trap spectral position in CdS. The waveguiding beam is used as a probe beam and we used the third harmonics of a YLF:Nd laser (347 nm) as a pump. The influence of bimolecular recombination on repopulation of deep traps is demonstrated. The linear recombination time as well as bimolecular and Auger coefficients are determined.

Linear optical properties (absorption and refractive index) of nanocrystalline CdS particles embedded in a silica thin film prepared by a sol-gel technique are presented. Three important parameters of elaboration are particularly pointed out: gelification time, the number of deposited layers and the semiconductor particles volume concentration up to 29%. The values of the refractive index as determined by m-line spectroscopy versus concentration, are analyzed in terms of the Maxwell-Garnett theory.

Crack free, transparent and crystallized sol-gel derived PbTiO3 thin films were deposited on pyrex slide using the dip-coating technique. Both PbTiO3 and Pb2Ti2O7 phases were formed on monolayers whereas only pure PbTiO3 perovskite was observed when depositing multilayers. Films microstructure consisted of a dense and polycrystalline layer with grain size of about 80 Angstrom. Monolayers (about 120 nm thick) were monomode TE and TM with a refractive index around 2.01. Best optical waveguiding (over 10 mm) was achieved with monolayers when TM polarized light propagates and an optical loss of 7.5 +/- 0.8 dB/cm was measured for the TM(0) mode.

Pure and porous silica xerogels doped with CdS nanocrystals have been prepared by a sol-gel process. In order to determine parameters convenient for non-linear optical properties, particle size distributions were obtained by two complementary techniques: transmission electron microscopy (conventional, CTEM, and high resolution, HRTEM) and small angle X-ray scattering (SAXS). Monolithic samples having CdO concentrations varying from 5 to 20 wt% have been studied. Details are given of an image analysis technique used to study the CTEM micrographs.

Samples of CdS doped silica thin films have been prepared with weight concentrations ranging from 0.5 to 20% (CdO/SiO2). Nanocrystal structure and size distribution are determined by Transmission Electron Microscopy (TEM) and image analysis. The mean size is tile same for all concentrations (4 nm) and is related to the matrix porosity. The linear absorption shows characteristic features of the excitonic level and the gap blue shift due to the quantum confinement. Non-linear optical properties are studied by Degenerate Four Waves Mixing (DFWM) to measure the third order susceptibility chi((3)) which is high (typically 10(-7) esu) and depends linearly of the volume fraction of the semiconductor particles.

Starting from alkoxides prepared in the laboratory, undoped and Sb-doped tin dioxide (SnO2) thin films have been deposited using the sol-gel dip-coating method. These layers have been characterized in relation to the environmental conditions during the pulling phase of the process. Among other parameters, the relative humidity ratio in the dip-coating apparatus has been found to be a key factor, for the morphology of the films as well as for the introduction of Sb-doping atoms. Characterization has been carried out by scanning electron microscopy, high resolution transmission electron microscopy and electron spectroscopy for chemical analysis.

The factors governing the existence of metastable cubic and tetragonal phases in zirconia powders are still controversial. In order to elucidate this question, the effects of calcination temperature on ultrafine powders prepared from different precursors by different low-temperature chemical routes were studied. The morphological and structural characteristics of the powders depending on the calcination temperature were determined by means of conventional and high-resolution transmission electron microscopy (CTEM and HREM) and X-ray diffraction methods (whole and peak profile fitting procedures). Important structural differences between the powders depending on the precursor were revealed by HREM. The presence of impurities and/or microstrains seems to play a major role in the stabilization of the cubic and the tetragonal phases.

Submicron ZrO2 powders by thermal decomposition of two zirconium acetates of different compositions and crystallographic natures. In both cases, the phase transformations were the same, i.e. crystalline or amorphousacetate → amorhousZrO2 → tetragonalZrO2 → monoclinicZrO2; however, important morphological differences between the two powders were observed by transmission electron microscopy. The carbon content of the precursor seemed to play an important role in determining the morphology of the powders. Samples with increased and with reduced carbon content respectively, were studied to clarify this effect.