Cerium-doped SrHfO3 sol-gel films

Abstract

SrHfO 3 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 Ce 3+ -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 SrHfO 3 orthorhombic phase at 750°C. The HfO 2 monoclinic phase superposes to SrHfO 3 orthorhombic phase after heat treatment performed at 1000°C. Finally, the potentiality to prepare Ce 3+ activated SrHfO 3 sol-gel films with scintillation properties is explored.Keywords: SrHfO 3 , sol-gel, thin films, planar waveguide, scintillating film. INTRODUCTIONThe alkaline earth hafnate is a perovskite type compound (Sr The scintillating films can be obtained via sol-gel route [6] which allows the use of a large number of substrates. Sol-gel process arises as an elaboration method for high quality oxide materials. Moreover, the incorporation of doping agents with a good homogeneity at the molecular scale is very easy. This process is also well adapted to the preparation of very good quality thin films used as planar waveguides [7]. In addition, we take advantage of waveguide performances of the elaborated films to study the optical properties of sol-gel cerium-doped SrHfO 3 . On one hand, it is well known that the optical properties of layers (refractive index, optical loss, etc.) are strongly dependent on the microstructure of the material. Therefore, several criteria such as porosity, grain size and grain boundaries must be taken into account to improve the performance of the films. On the other hand, well identified crystalline phase is necessary to improve scintillation properties of the films. Our layers were structurally characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The refractive index and the thickness of the waveguiding solgel films were determined by m-lines spectroscopy (MLS). EXPERIMENTAL PROCEDURE Preparation of Ce 3+ -Doped SrHfO 3 Sol-Gel FilmsThe starting solution was prepared using a stoichiometric mixture (Sr/Hf=1) of hafnium tetraethoxide (Hf(OC 2 H 5 ) 4 ), (99.9%-Gelest) and strontium ethoxide, (Sr(OC 2 H 5 ) 2 ). Cerium nitrate pentahydrated (Ce(NO 3 ) 3 , 5H 2 O), (99.9%-Aldrich) is added as dopant in order to obtain a 1%mol concentration. The used

High-temperature phase transitions in SrHfO 3 : A Raman scattering study

“…thermal hysteresis or latent heat and that the structure does not become disordered in normal annealing (which is anywhere from 700 to 1450 K) [4,5]. Any disordering would degrade channel mobility in SHO-based n-FET and probably the dielectric constant of the final film, whereas a first-order transition might produce cracking.…”