Synthesis of Fe(1-x)Znx@Zn(1-y)FeyOz nanocrystals via a simple programmed microfluidic process

Abstract In this paper, Fe (1-x) Zn x @Zn (1-y) Fe y O z nanocrystals were successfully synthesized via a simple programmed microfluidic process (SPMP). The sizes, shapes, crystal structures and surface compositions were characterized by transmission electron microscope (TEM), energy dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the Fe (1-x) Zn x @Zn (1-y) Fe y O z nanocrystals (NCs) were mainly composed of iron-rich FeZn alloys and surface coatings are mainly formed by the Fe-doped ZnO. These nanocrystals preserved unique Fe/Zn ratio dependent optical and magnetic properties. A visible green emission at 530 nm and a weak violet emission at 425 nm were observed in the photoluminescence (PL) spectra due to the radiative transition of electrons from antisite defect (O Zn ) and zinc interstitial defects to the conduction band, respectively, as compared to that in pure ZnO (∼379 nm). The PL intensities of these nanocrystals can be increased significantly with the increase of the Zn contents in nanocrystals. The Fe (1-x) Zn x @Zn (1-y) Fe y O z nanocrystals with a Fe/Zn atom ratio of 2.6/1 preserved the ferromagnetic property, which can be attributed to the high Fe content, varieties of defects caused by ZnFe 2 O 4 shells and the interaction between the shell and FeZn alloy cores. With the decrease of iron content, the coercivities of nanocrystals decreased distinctly.