*3.3.7 O 1s XPS spectra*

In order to examined the presence of oxygen vacancies, VO, the O 1s XPS spectra of pure ZnO, Zn0.95Fe0.05O (ZFO5) and Zn0.92Fe0.05La0.03O (ZFLaO53) nanoparticles are given in **Figure 10** [47]. It deconvoluted into three peaks (Oa, Ob, Oc). The peak located on the low binding energy side (Oa) around 529.73 eV is attributed to O2<sup>−</sup> ions on the wurtzite structure. The Ob peak at about 530.65 eV is associated with O2<sup>−</sup> ions in oxygen-deficient regions within ZnO matrix, which indicate the formation of defects. The Oc peak at about 531.37 eV is usually attributed to chemisorbed oxygen on the nanostructural surface of the ZnO, such as adsorbed –CO3, H2O or adsorbed O2 [66, 67].
