Eu³⁺ as optical probe of the structure in amorphous and nanocrystalline ZnO sol-gel films

Amorphous and nanocrystalline Eu³⁺-doped ZnO thin films were synthesized by the sol-gel process. The films were spin-coated on glass substrates. The samples were annealed at 500°C for 1 hour to produce a nanocrystalline ZnO/Eu³⁺ films. The samples were characterized using UV-Vis absorption and infrared spectroscopy. A crystalline phase, wurtzite, was detected by X-ray diffraction. A spectroscopic study of the Eu³⁺ impurity in function of the heat treatment provided to the ZnO matrix was done. Results of emission and excitation studies at room temperature of Eu ³⁺ inserted in the ZnO matrix are presented. For amorphous and nanocrystalline samples, the relative ratio of the ⁷F ₂/⁷F₁ transitions was calculated. The evolution of this ratio was interpreted in terms of the Eu³⁺ symmetry site change when the nanocrystalline ZnO films. This fact was confirmed measuring the Eu³⁺ lifetimes.