Characteristics and optical properties of iron ion (Fe3+)-doped titanium oxide thin films prepared by a sol–gel spin coating

Titanium dioxide (TiO2) thin films doping of various iron ion (Fe3+) concentrations have been prepared on a glass substrate by the sol–gel spin coating process. Characteristics and optical properties of TiO2 thin films doping of various Fe content were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–vis) and spectroscopic ellipsometry. The crystalline phase of TiO2 thin films comprised only the anatase TiO2, but the crystallinity decreased when the Fe3+ content increased from 0 to 25.0 wt%. During the Fe3+ addition to 25.0 wt%, the phase of TiO2 thin film still maintained the amorphous state. The absorption edge of TiO2 thin films shifted towards longer wavelengths (i.e. red shifted) from 355 to 415 nm when the Fe3+-doped concentration increased from 0 to 25.0 wt%. The values of the refractive index (n), and extinction coefficient (k), decreased with an increasing Fe3+ content. Moreover, the band-gap energy of TiO2 thin films also decreased from 3.29 to 2.83 eV with an increase in the Fe3+ content from 0 to 25.0 wt%.