Luminescence, structure and insight on the inversion degree from normal to inverse spinel in a ZnAl_(2-x)Fe_x³⁺O₄system

ZnAl2O4 doped with various concentration (x) of Fe3+ were prepared using the Pechini synthesis. In the first set of samples, Fe3+ substituted Al3+ to create a system of the form ZnAl(2-x)Fex3+O4 (x = 0-0.08). To study the effect of charge compensation, Fe3+ substituted Zn2+ to create Zn(1-x)Fex3+Al2O4 (x = 0.05) system. The structure and particle morphology of the phosphors were studied using X-ray diffractometer (XRD) and field emission scanning electron spectroscopy, respectively. From the XRD data, the oxygen parameter and the inversion degrees were estimated. The elemental composition and electronic states of the phosphors were analyzed using X-ray photoelectron spectroscopy (XPS). XPS results showed that part of the Fe3+ were reduced to Fe2+ in the doped samples. Both photoluminescence and cathodoluminescence properties of the phosphors were also studied. Luminescence excitations using a xenon lamp and X-ray showed two broad emission bands located around 470 and 730 nm, and were ascribed to Fe ions occupying the tetrahedral (tet) and the octahedral (oct) sites in ZnAl2O4, respectively. A change in the lifetime of these two emission bands upon Fe doping further confirmed the existence of Fe in the tet and oct sites in the ZnAl(2-x)Fex3+O4 matrix.