By using polyvinylpyrrolidone (PVP) as the nucleation promoter and directing agent, the shape-selective synthesis of ZnO has been realized at 35 degrees C. By simply modifying the amount of PVP or/and water, the product shape can be readily changed from one-dimensional structure via monolayer and semi-bilayer to bilayer structure with controlled aspect ratio (defined as monolayer thickness/edge length). As shown by both the photoluminescence and absorption spectra, the ZnO band gap can be modified by adjusting the sample shape. The low-temperature route reported here should open an effective and low-cost approach to the ZnO with tunable shapes and band gaps. (c) 2008 Elsevier B.V. All rights reserved.