Structural, Optical and EPR Study of Zn1−xFexO Nanocrystals

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Iron-doped ZnO nanocrystals, ZnO (Zn1−xFexO), with doping atomic ratio x = 0.0–0.05, have been synthesized using the sol–gel method to obtain nanoparticles with an average crystal size of around 38.0 nm. Materials were characterized by X-ray fluorescence, Raman and Fourier transform infrared (FTIR) spectroscopies, diffuse reflectance spectroscopy and continuous-wave electron paramagnetic resonance (EPR). FTIR spectroscopies suggest minor change in the Zn–O band occurring in the ZnO environment when the ZnO is Fe doped. X-ray diffraction measurements indicate that lattice parameters of Fe-doped ZnO do not change for all doping levels x. Raman studies show that no peaks disappear when Fe concentration increases, indicating that the incorporation of Fe does not cause an important local structural disarray in the crystalline ZnO lattice. Two broad bands appear at ≈ 570 cm−1 and ≈ 650 cm−1, which are related to the Zn substitution by iron. The band gap does not seem to be influenced by the average crystal size or the cell parameter. It could be because the crystal size is large enough to prevent quantum confinement. X-band EPR spectra recorded at 10 K are similar for all doping levels, x = 0.01–0.05, and are consistent with a spin Hamiltonian composed by isotropic Zeeman and second-order axial symmetry zero-field splitting (ZFS) interactions. Due to the small size of the particles and the difference between the ionic radii of Fe3+ and Zn2+, the EPR spectra are strongly influenced by a static distribution of ZFS parameters, leading to a severe lineshape broadening. An efficient strategy for the simulation process is explained in detail.