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 TiO ₂/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.