Synthesis of Fe–Pr co-doped ZnO nanoparticles: Structural, optical and antibacterial properties

Photoresponsive Activity of the Zn0.94Er0.02Cr0.04O Compound with Hemisphere-like Structure Obtained by Co-Precipitation

“…In the present study, peaks appear at 501, 539, 620 and 678 cm −1 , which may be associated with oxygen vacancy (V o ) defects that arise from the difference between the oxidation states of the dopant cations and the host cation [ 44 , 45 ]. This conclusion is also based on the results reported by Rocha et al [ 37 ] for pure ZnO structures, since for the region marked in Figure 1 b (defect region), the authors did not observe characteristic peaks of the optical mode frequencies of the Brillouin zone for the wurtzite structure.…”

“…The lattice parameters ( a and c ) are calculated using the equation that correlates the interplanar spacing, Miller indices and the lattice constants for the ZnO with hexagonal structure [ 36 ]. The calculated values for a and c are 3.2468(1) Å and 4.9482(3) Å, respectively, which are smaller than the recently reported values for ZnO [ 37 ]. This indicates that the dopants’ insertion into the ZnO host lattice produces structural distortions that can be associated with the difference between the ionic radii of the dopant cations (Er 3+ (0.89 Å) and Cr 3+ (0.62 Å)) and the Zn 2+ (0.74Å) host cations [ 38 ].…”

“…The Scherrer equation [ 36 ] was used to estimate the average crystallite size (D) and the value obtained was 86 nm. This result is four times higher than the value reported for ZnO nanostructures by Rocha et al [ 37 ]. The Er and Cr ions’ insertion in the ZnO structure can be classified as the donor’s dopants because they have more of an oxidation state, if compared to the Zn ions.…”

“…The yellow emission at ~573.4 nm (2.16 eV) originates from V o + and the orange-red emission at ~639.9 nm (1.94 eV) derives from V o ++ . Finally, the peak centered in the red region at ~694.3 nm (1.79 eV) can be attributed to O i [ 37 ]. The simplified scheme of the transitions from the conduction band to the valence band is represented in Figure 2 b.…”

“…The calculated value (3.323 ± 0.001 eV) is in agreement with the value reported for ZnO bulk (3.35 eV) [ 49 ]. However, a comparison with the value reported by Rocha et al [ 37 ] indicates that the Er and Cr inclusion in the ZnO host lattice can cause an energetic competition, which allows the Fermi level to move for the conduction band, increasing the concentration of carriers and causing an increase in the optical gap [ 56 ]. Similar results have been observed by different authors for doped ZnO structures [ 49 , 56 ].…”