The white light caused by defects and complex cation distribution in ZnAl_2-xFe_xO₄ magnetic nanocrystals

ZnAl₂O₄ with spinel structure has attracted more attentions due to its robust dielectric and luminescence properties. Complex cation distribution in spinel structure influences the optical and magnetic properties. Herein, we report white emission related to the defects and the magnetism assigned to Fe impurity in ZnAl_2-xFe_xO₄ ($0⩽x⩽0.6$) nanocrystals fabricated by using common sol-gel method at a relatively lower temperature (700 °C) than that reported earlier. ZnAl_2-xFe_xO₄ phosphors reveal single spinel phase without impure phase. Complex cation distribution is observed in all samples, for instance, Fe and Zn in antisites, cation vacancies, and with Fe content increasing, cation distribution reveals obvious change. The band gap energy of ZnAl_2-xFe_xO₄ phosphors is reduced from 3.84 eV to 3.33 eV when the content of Fe ions (x value) increases from 0 to 0.6. Two wide band emissions assigned to the various types of shallow and deep donor/acceptor defects are observed, monitoring with the excitation wavelength of 280 nm. The Commission International de I'Eclairage (CIE) colour coordinate (x, y) of the ZnAl_2-xFe_xO₄ phosphors is found to shift from (0.3218, 0.2957) to (0.3422, 0.3122) with Fe doping in spinel lattices owing to rearrangement of defects, indicating the potential application in white-light illumination. ZnAl_2-xFe_xO₄ reveals a room ferromagnetism resulting from Fe3 + ions in spinel lattices. (paper)