Digest Journal of Nanomaterials and Biostructures Vol. 14, No.1, January - March 2019, p. 119 - 125 STUDY OF OPTICAL ENERGY GAP AND QUANTUM CONFINMENT EFFECTS IN ZINC OXIDE NANOPARTICLES AND NANORODS I. MUSA * , N. QAMHIEH a Department of Physics, Palestine Technical University-Kadoorie, Tulkarm, P.O. Box 7, Palestine b Department of Physics, UAE University, Al-Ain, P.O. Box 15551, United Arab Emirates ZnO sol-gel nanoparticles (NPs) and nanorods (NRs) were prepared by simple chemical method. The resulting NPs and NRs have been characterized by X-Ray Diffraction, TEM, UV-Vis absorption and steady-state photoluminescence (PL) spectroscopy.(XRD) results showed that all samples were single phase wurtzite structure and broadening peaks for ZnO nanoparticles as compared to NRs. The morphology of the nanostructures was observed in transmission emission microscope. The NPs have average diameter ~ 4 nm and the NRs have ~ 18 nm diameter and ~ 100 nm length. The band gap was calculated from the UV-Visible spectrum and found to be 3.39 eV for NPs and 3.2 eV for NRs. This variation of optical energy gap is due to quantum confinement effect when is the material changed from nanoparticles to nanorods. However, the measured NPs and NRs diameters indicate that the charge carriers are located in a strong and weak confinement regime, respectively.The PL reveals that the ultraviolet emission intensity of ZnO nanoparticles decreases from 396 to 367 nm and shifts towards the blue region by reducing the size as compared to nanorods which is consistent with UV-visible absorption. (Received October 16, 2018; Accepted February 14, 2019) Keywords: Nanoparticles, Nanorods, Optical band gap, Steady-state photoluminescence 1. Introduction Wurzite zinc oxide (ZnO) is a well-known semiconductor material, with research going back to the first quarter of the last century [1]. It belongs to the group of II-VI compound with a direct- wide bandgap (WBG)semiconductor ( E g ~ 3.37 eV) at room temperature [2]. In the last decade, research interest in ZnO nanostructure was regenerated because of the processing method used to fabricate ZnO lead to different properties. It attracted great attention in research due to its unique properties and versatile application in biomedical [3], piezoelectronic devices, transparent electronics, and chemical sensors [4,5]. Also, ZnO possesses high exciton binding energy of (60 meV) at room temperature which makes it promising in applications like optoelectronic devices [6,7]. Furthermore, ZnO has a large number of extrinsic and intrinsic deep-level impurities that emit light of different colors, including violet, blue, green, yellow, orange and red [8,9]. Another area of interest is based on the length scale of the ZnO nanostructure. When the size of semiconducting-nanostructuers is reduced to the order of Bohr radius of bulk exciton(few nanometers), quantum confinement effect occurs and the optical properties of exciton are changed. This effect was observed by Berry [10,11]and Brus [12] for reduced size nanocrystals in a colloidal dispersion. The quantum confinement can be related to the increase of the band gap when the particle size decreases, which causes a blue shift of the emission as a result of bandgap widening. The quantum confinement depends on the ratio of the nanostructuers radius to Bohr exciton radius of the bulk. It can be classified to weak, intermediate and strong confinement regimes [13,14]. * Corresponding author: i.musa@ptuk.edu.ps