Growth, characterization and optical properties of nanocrystalline gadolinia thin films prepared by sol-gel dip coating

Nanostructured gadolinia thin layers with small sized crystalline grains (circle divide approximate to 3-13 nm) were successfully prepared by the sol-gel process on fused silica and silicon substrates. The film growth, the chemical composition, the morphology and the microstructure of the films were investigated in detail by thermo-gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and x-ray diffraction. The experimental results clearly show that the morphological and structural properties of the films are not influenced by the substrate properties and the Gd2O3 cubic crystalline phase (symmetry group Ia (3) over bar) s enhanced when the films are free from organic residuals and decompose to Gd-oxides. FTIR analysis of gadolinia layers grown on silicon suggest that the formation of Gd2O3 grains may favour the diffusion of oxygen through the coatings. The optical spectroscopy measurements evidence a blue shift of the energy gap and suggest a quantum confinement effect in nano-sized Gd2O3. In addition, two absorption features are observed, which can be attributed to a simultaneous presence of direct and indirect electronic transition indicating a modification of the band structure when the grain size changes from very small to larger Gd2O3 grains.