Evidence of progressive Fe2+ to Fe3+oxidation in Fe2+-doped ZnO nanoparticles

Oxide-diluted magnetic semiconductors have received considerable attention in diverse scientific and technological fields because they combine the optoelectronic properties of the hosting semiconductor with the magnetic properties of the metal dopant. In this report, the role of Fe doping on the structural, vibrational, optical, hyperfine, and magnetic properties of Fe-doped ZnO nanoparticles (Zn1-xFexO) synthesized via a polymeric precursor method is presented. Our findings display that the crystallite size decreases from similar to 23 nm (x = 0.000) to similar to 8 nm (x = 0.200) as the Fe-content (x) is increased. From the XRD data analysis, our results suggest an isovalent solid solution between Fe2+ and Zn2+ ions for lower Fe-content (up to 0.075) and aliovalent solution (Fe3+ and Zn2+ ions) for higher Fe-content. Elliot's theory was used to assess the band gap energy of E-g similar to 3.4 eV, and an exciton binding energy of E-b similar to 66 meV for the undoped sample. The excitonic peak exhibits a broadening trend with increasing Fe-content, suggesting disorder enhancement in the ZnO matrix. Besides, FTIR data analysis suggests that the Zn-O bond length increases with Fe-content up to 0.075 and decreases above this value. The intensity ratio of the O-H and Zn-O modes shows a discontinuity as the Fe-content is increased. Room temperature Mossbauer spectra carried out for samples with x = 0.050, 0.075, and 0.200 show that the isomer shift and quadrupole splitting increase with the Fe-content, in agreement with the structural properties. Magnetic measurements suggest that the iron ions stabilize as Fe2+ in samples with low Fe-content and then as Fe3+ in samples with high Fe-content. Besides, the occurrence of short-range antiferromagnetic interactions was determined, which becomes stronger as the Fe-content is increased.

Automated summary

Oxide-diluted magnetic semiconductors, specifically Fe-doped ZnO nanoparticles, were synthesized and investigated to understand the effect of Fe doping on their structural, vibrational, optical, hyperfine, and magnetic properties. The results showed that increasing Fe content led to a decrease in crystallite size. XRD analysis revealed different solid solution phases for low and high Fe content. Elliot's theory was used to determine band gap energy and exciton binding energy. FTIR analysis indicated changes in Zn-O bond length and intensity ratio of O-H and Zn-O modes with Fe content. Mossbauer spectra and magnetic measurements showed stabilization of iron ions and the presence of antiferromagnetic interactions.