Nickel doping induced amorphization of brookite TiO2: Photoluminescence enhancement

Abstract

In this work, we have elaborated nickel doped TiO2 thin films by low temperature spray pyrolysis technique from ethanol based precursor. For the sample free of nickel, The FTIR spectrum reveals a large amount of organic species bonded to TiO2, resulting in a carbon-doped brookite. Ni doping causes extinction of the organic related peak that fade away for highly (> 10 %) Ni doped films. XRD spectra reveal the presence of brookite phase for low Ni amounts. While increasing Ni rate, the crystalline phase undergoes a transition to amorphous state and brookite XRD peaks vanishes. Optical and electronic (SEM) micrographs show a smooth surface with small brookite nanoparticles, for low Ni rate. Increasing Ni rate results in a fractured morphology composed of micrometric smooth ships. Optical absorption obtained by transmittance-reflectance spectra is enhanced in the transparency region of TiO2, by Ni doping due to the increase of defect density and the brookite to amorphous phase transformation. Visible and UV emission spectra are obtained from PL measurements at room temperature. A spectacular PL magnification is obtained for high Ni doping levels due to increase of oxygen vacancies in the amorphous film. However, thermal annealing at 500 °C causes recrystallization to anatase phase, leading to a dramatic PL quenching.