Controlled growth and properties of one-dimensional ZnO nanostructures with Ce as activator/dopant

A large amount of one-dimensional (1D) Ce-doped ZnO nanostructures with different morphologies has been successfully synthesized by annealing a polymeric precursor at various temperatures. The evolution of the morphologies and microstructures was investigated by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results show that the morphologies vary drastically with increasing synthesis temperature and the photoluminescence (PL) of the products depends on both the synthesis and measurement temperatures. The CeO layer forms first and becomes a catalytic center for the ZnO growth. At a synthesis temperature lower than the boiling point of Zn, Zn and O atoms can stack epitaxially along the CeO catalytic layer and form a bicrystal nanobelt-like structure with a trapezoid-like end and a concave growth fault center. At a synthesis temperature higher than the boiling point of Zn, however, nanowires with an incommensurately modulated superstructure are obtained due to the high reaction rate and the formation of a periodic separation of the CeO layer. As for the room-temperature PL of ZnO, the incorporation of donor Cc leads to the disappearance of the green band and the appearance of a purplish-blue emission peak, whose position shifts towards the red and whose intensity decreases with increasing synthesis temperature. Analysis of this temperature-dependent luminescence indicates that the purplish-blue emission of nanobelts prepared at 850degreesC originates from a donor-bound exciton emission, and, contrary to the nanowires, it undergoes a change from an emission of the electron-hole plasma (EHP) to an emission of the donor-bound exciton with decreasing measurement temperature.