Optical investigation of various morphologies of ZnO nanostructures prepared by PVP-assisted wet chemical method

Various morphologies of zinc oxide have been successfully synthesized via simple poly-vinylpyrrolidone (PVP) assisted wet chemical method. Herein, a comparative study between three different morphologies of ZnO, namely nanoparticles (NP’s), nanowalls (NW’s) and nanorods (NR’s) has been presented. The structural and spectroscopic results reveal that the addition of PVP as capping agent greatly influences the structural and optical behavior of ZnO. X-ray diffraction (XRD) results confirmed pure phase ZnO nanostructures with well crystallinity. It was observed from results that increasing concentration of poly-vinylpyrrolidone from half to equimolar ratio lattice imperfections decrease. ZnO nanorods have biggest crystallite size compared with nanowalls and nanoparticles, confirmed through X-ray diffraction study. The formation of three different morphologies was observed through scanning electron microscopy (SEM). The FTIR and Raman spectroscopic results reveal significant shifts for these ZnO nanostructures in the typical modes assigned to Zn-O, which intercorrelated with the XRD results. The optical band gap energies were found to be decreased from ∼3.22 eV for ZnO nanoparticles to 3.14 eV for ZnO nanorods. It was investigated from photoluminescence study that PVP capped ZnO nanostructures have reduced surface trap states and therefore the UV emission and visible emission regions overlap to form a single band. The physical properties and optical behavior realized that, as prepared samples might be applied in energy storage devices and solar cells.