The role of pH on the vibrational, optical and electronic properties of the Zn1-xFexO compound synthesized via sol gel method

Herein, was investigated the role of pH on vibrational, morphological, optical, and electronic properties for pure and Fe-doped ZnO nanoparticles. The Zn1-xFexO compound with x = 0.00 and 0.02, were synthesized by the sol gel method with pH = 3, 6 and 9. For pure (x = 0.00) and Fe-doped (x = 0.02) ZnO samples Raman spectra showed slight variations, as the pH changed from the acidic to alkaline state. Two vibrational modes (580 cm−1 and 650 cm−1) were observed for Fe-doped samples, with shifted increasing as the pH values grow. Fourier transform infrared analysis revealed functional groups confirming the ZnO hexagonal structure for all x values. The samples corresponding to lower pH values showed spherical particles that are self-assembled to form irregular three-dimensional prisms-like, while the samples synthesized with basic and alkaline pH, the spherical nanoparticles are self-assembled in plates meshes-like. Pure and Fe-doped samples showed optical band gap values lower than expected for the bulk ZnO, with the lowest values for compounds synthesized at acidic pH (band gap = 3.23 ± 0.05 eV for pure ZnO and 3.21 ± 0.06 eV for Fe-doped ZnO). Structural defects such as zinc vacancies, interstitial zinc, singly ionized oxygen vacancy, and doubly ionized oxygen vacancy were detected through the photoluminescence spectra. The pH effect on electronic properties for pure and Fe-doped ZnO nanoparticles was also confirmed by electron paramagnetic resonance (EPR) measures. The simulation of EPR data for the spin S = 5/2 (Fe3+) demonstrated that pH variation induces strains in the ZnO lattice.