Study on the Fabrication and Properties of Eu-Doped Indium Oxide Films by Sol–Gel Method

Rare-earth elements are often used as dopants because of their good properties. We prepared six sets of In₂O₃ thin films with different Eu-doped concentrations by the sol–gel method. We investigated the effects of Eu-doping on the crystal structure, surface morphology, elemental composition, and optical properties of the films. The results showed that the In₂O₃ films with different doping concentrations have good crystallinity and maintain a preferentially oriented cubic crystal structure along the (222) plane. With the increase of doping concentration, the intensity of the (222) diffraction peaks slightly decreased, and the films gradually tilted to the amorphous state. The Eu-doping made the sample surface more compact and smooth, reduced the porosity, increased the crystallite size, and improved the transparency and optical homogeneity of the films. From the XPS spectra analysis, it can be concluded that the doping of Eu did not produce obvious changes in the fitted peaks of O 1s, indicating that Eu³⁺ successfully replaced In³⁺ in the In₂O₃ films. The optical transmittance and bandgap both increased with the increase of doping concentration, the transmittance from 83% to 91%, and the bandgap from 3.74 eV to 3.79 eV. All the samples showed blue-green luminescence bands around 400 nm, and the intensity of the luminescence peaks reached the highest at 3% doping concentration, which was beneficial for the improvement of the optical properties with the appropriate amount of doping. In our study, Eu-doped improved the physical properties of In₂O₃ thin films, which is of great research significance.