Hydrothermal Synthesis of Zinc Blende Phases in Wurtzite ZnO Phases and Their Temperature-Dependent Photoluminescence

Microstructure and surface morphology of ZnO nanorods, which were synthesized on glass substrates using a hydrothermal method, have been characterized by X-ray diffraction and scanning electron microscopy. The ZnO nanorods possess wurtzite structure with the preferential orientation of (002) plane and zinc blende structure with the (111) plane. The ZnO nanorods has a large number of defects so that a stronger and broader visible emission band in the energy range of 1.5 to 2.5 eV has been observed in the room temperature PL spectrum, and the ratio of the intensity of near band edge emission (I-UV) to that of deep level emission (I-DL) is estimated to be 0.38. The temperature-dependent photoluminescence spectra show that both the near band edge emission and the deep level emissions decrease with increasing temperature. The decrease in the intensity of donor bound excitons ((DX)-X-0) associated with the thermal dissociations of (DX)-X-0 into free excitons (FX) with increasing temperature. The redshift of FX emission with increasing temperature can be ascribed to the temperature-induced band-gap shrinkage. The decrease of visible emission bands with increasing temperature can be attributed to prolonging the radiative lifetime and/or shortening the non-radiative lifetime.