Cobalt doped zinc oxide nanorods Zn1-xCoxO (x = 0.01, 0.10) have been synthesized by a
hydrothermal process with Zn(NO 3)2, Co(NO3)2, NH4OH, CO(NH2)2 and C2H5OH at 150 °C for 1 h. Xray
diffraction and scanning electron microscopy were used to characterize the crystalline structure, size and
morphology of the samples. The photoluminescence (PL) and the PL excitation spectra of the nanorods were
measured in the range of temperature from 15 K to room temperature. The PL spectra at low temperatures
exhibit a group of ultraviolet narrow lines in the near-band-edge region of 3.0-3.4 eV and a very broad band
peaked at 3.20 eV. The origin of the near-band-edge PL is interpreted as an emission from free excitons,
neutral donor-bound excitons, radiative transitions from a donor to the valence band and donor-acceptor
pairs. In particular, a group of emission lines in the red region of 1.8-1.9 eV have been revealed. These
emission lines were assigned to the radiative transitions within the tetrahedral Co 2+ ions in the ZnO host
crystal
