Polychromatic visible photoluminescence in porous ZnO nanotubes

In this paper, we report the photoluminescence (PL) properties of porous ZnO nanotubes prepared by a two-step hydrothermal method. The nanotubes show a nearly homogeneous size of about 250 nm diameter, 50 nm wall thickness and 500 nm length. There are always some scattered nanoholes with sizes ranging from several tens of nanometres to about 200 nm on the side wall of each nanotube. A polychromatic PL band consisting of blue, green and orange emissions was realized by introducing the unwanted native defects into the ZnO lattice. Both the porous structure and the production of the unwanted defects are closely correlated with the non-equilibrium reaction condition during the preparation of porous ZnO nanotubes. The origin of the polychromatic PL was discussed together with the measurements of the PL features of the nanotubes annealed at different atmospheres and the lifetime of the three visible emissions. Porous ZnO nanotubes with polychromatic emission are expected to find much potential application in UV-excited wide-spectrum phosphors.