Abstract: Because of the extremely sensitivity to the local environment of the ⁵D₀→⁷F₂ transition of Eu³⁺ ion, the fluorescence
of Eu³⁺ ions was studied by introducing Eu³⁺ ions to TiO₂ gel by the sol-gel method, from which the structural changes of TiO₂ gel
were characterized. The results showed that the intensity of ⁵D₀→⁷F₂ transition increased with the increasement of heat treatment temperature,
which indicated the evaporation of molecular water and the completeness of the condensation reaction. Because of the quenching of the fluorescence
induced by the cluster of Eu³⁺ ions, the addition of Al³⁺ ions greatly enhanced the emission intensity of Eu³⁺ ion.

Key words: fluorescence probe, TiO₂ gel, symmetry