Strong and unusual violet-blue emission in ring shaped ZnO nanocrystals

ZnO nanorings, relatively well dispersed, have been grown without any template by adopting a soft chemical route mediated by cetyltrimethylammonium bromide (CTAB). As-synthesized materials have been extensively characterized by X-ray diffraction (XRD), UV-visible (UV-Vis) absorbance studies, Fourier transform infrared analysis (FTIR), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) studies. Both XRD and HRTEM indicate that ultrafine ZnO nanoparticles coalescence into the nano-rings which are crystalline in nature and oriented along the (101) direction. The observed UV-Vis spectra show a blue shift for these nano-rings. Room temperature photoluminescence measurements show violet blue emission related to the structural defects, which can barely be observed. Some new emission features are uncovered and a possible mechanism to explain it is briefly discussed with the help of a band model proposed on the basis of experimental results.