C. Le Luyer

Elaboration and scintillation properties of Eu3+-doped Gd2O3 and Lu2O3 sol–gel films

Abstract High-resolution X-rays imaging requires thin films of dense materials with high light yield under X-ray excitation. Polycrystalline films of europium-doped gadolinium and lutetium oxide have been prepared by sol–gel method. The scintillation performances of these compounds for X-rays imaging are presented and discussed.

Optical properties of europium-doped Gd2O3 waveguiding thin films prepared by the sol–gel method

Abstract 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.

Preparation and characterization of sol–gel Y2O3 planar waveguides

Abstract Y2O3 thin film waveguides were prepared using a sol–gel method and a dip-coating procedure. Multicoating operations were necessary to produce multimode and low attenuation coefficient waveguides. Thickness and refractive index were determined by m-lines spectroscopy. X-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) were used for structural investigations and nanocrystals size determination as a function of the annealing temperature. The Y2O3 amorphous phase was observed at low heat-treatment temperature (300°C) and the layers turn to cubic nanocrystalline form when the annealing temperature reached 400°C. An annealing treatment at 600°C was necessary to provide more densified and good optical planar waveguides exhibiting an attenuation coefficient lower than 2 dB/cm.

Annealing and doping effects on the structure of europium-doped HfO2 sol–gel material

Abstract Powders and waveguiding films of europium-doped hafnium oxide (Eu3+:HfO2) are prepared by a sol–gel process. The material is synthesized using hafnium tetra-ethoxide and europium (III) nitrate pentahydrate which are dissolved in ethanol and mixed with acatylacetone. The powders and the films present structural changes depending on Eu3+ concentration and annealing temperature. The monoclinic stable phase appears at low annealing temperatures and is preferentially crystallised for low doping concentrations. The tetragonal phase appears at high annealing temperatures and is the predominant phase for high doping concentrations. Differential thermal analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy are used to characterize the powders and the films.

A thick sol–gel inorganic layer for optical planar waveguide applications

Abstract The laponite films elaboration is based on the sol–gel process and dip-coating technique. The films are dried at 120°C and heat-treated at higher temperature up to 600°C without deterioration of their quality. Three micrometer thick and crack-free films are obtained in only one coating by dipping a substrate into a well-controlled viscous solution. By this way 9 μm high quality thick films have been prepared using three successive coatings and adapted heat treatment. These films exhibit light waveguiding properties. Differential thermal analysis (DTA) measurements conducted on the powder indicate water removal phenomenon at different annealing temperatures. These results are correlated with X-ray diffraction (XRD) analyses to explain preferential orientation and densification of the 600°C heat-treated layer. This structural behavior involves optical birefringence and refractive index increase of the film. Potentialities to use laponite films in planar optical waveguide field are presented.

Synthesis and properties of Lu2O3 sol–gel films

Abstract Lutetium oxide films have been prepared by the sol–gel method and the dip-coating technique. Transparent and crack free coatings are obtained. Differential Thermal Analysis and Infrared spectroscopy were conducted on the dried sol–gel solution in order to determine the structure dependence of the material with temperature. The film microstructure was studied by Raman microscopy and X-ray diffraction. The crystallization of the lutetium oxide phase occurs at 600°C. Opto-geometrical parameters were determined depending on the annealing temperature. After heat treatment at 1000°C, very dense lutetium oxide films are obtained exhibiting a refractive index around 1.8 at 543.5 nm and a thickness of 410 nm.

Cerium-doped SrHfO3 sol-gel films

SrHfO3 presents high density, which makes it interesting for host lattice when it is doped with rare earths for luminescent materials. The optical and structural studies of Ce3+-doped strontium hafnate films prepared by the sol-gel process are presented in this work. Crack-free films with waveguiding performances were obtained with heat-treatments between 400°C and 700°C. The total elimination of organic compounds occurs above 800°C as indicated by Fourier transform infrared spectroscopy. The optogeometric properties (refractive index and thickness) are investigated by m-lines spectroscopy. Films structure is analysed using X-ray diffraction and transmission electron microscopy. The films crystallise from amorphous phase to pure SrHfO3 orthorhombic phase at 750°C. The HfO2 monoclinic phase superposes to SrHfO3 orthorhombic phase after heat treatment performed at 1000°C. Finally, the potentiality to prepare Ce3+ activated SrHfO3 sol-gel films with scintillation properties is explored.