Evolution of ZnO nanoparticles and nanorods: aspect ratio dependent optoelectronic properties

Nanoscience Laboratory, Department of Physics, Tezpur University, P.O. Napaam, Tezpur 784028, Assam, India

Corresponding author: best@tezu.ernet.in

Received: 24 August 2010
Accepted: 6 October 2010
Published online: 23 December 2010

Abstract

Zinc oxide (ZnO) nanorods, with different aspect ratios, were synthesised at room temperature via an inexpensive physico-chemical route. The source material was a mixture of zinc acetate dihydrate [ Zn (CH₃ COO)₂  2H₂O] , cetyl-trimethyl ammonium bromide [ C₁₉H₄₂BrN] , and sodium hydroxide [NaOH]. The length of the nanorods, as a result of restricted directional growth, was controlled by means of varying the molar ratios of the reactants. As revealed by X-ray diffraction measurements, the as-grown ZnO nanorods exhibited wurtzite crystalline phase, with preferred crystallographic orientation along (101) plane. The visual evidence of the formation of ZnO nanorods was confirmed by transmission electron microscopy studies. The photoluminescence spectra of the ZnO systems show two prominent peaks: a sharp peak located at ~375 nm (UV band) and a broad band peaking at ~480 nm (green band). The UV-to-green PL intensity ratio was found to be improved with enhanced aspect ratio. The aspect ratio dependent tunable optical responses would provide better insight to understand the radiative and non-radiative processes in elongated nanosystems.