Eu~(3+) as optical probe of the structure in amorphous and nanocrystalline TiO_2 films prepared by sol-gel method

摘要

In this work the Eu~(3+) ion was used as optical probe, by considering its hypersensitive transitions to follow changes in the local environment. Eu~(3+) ions were incorporated into gel via dissolution of soluble species into the initial precursor TiO_2 sol. The TiO_2/Eu~(3+) films were spin-coated on glass wafers. A spectroscopic study of the Eu~( 3+) impurity in function of the heat treatment provided to the TiO_2 matrix was done. Anatase nanophase was obtained after heat treatment at 600°C for 1 h 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 Eu~(3+) inserted in the TiO_2 matrix are presented. The ratio of the ~7F_2/~7F_1 transitions was calculated. The evolution of this ratio was interpreted in terms of the Eu~(3+) symmetry site change when the nanocrystalline TiO_2 phase was obtained.