CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 40 (2014) 4327–4332 Optical properties of group-I-doped ZnO nanowires Abdolhossein Sa΄aedi a , Ramin Yousefi b,n , Farid Jamali-Sheini c , Mohsen Cheraghizade a , A. Khorsand Zak d , Nay Ming Huang e a Department of Electrical Engineering, Bushehr Branch, Islamic Azad University (I.A.U), Bushehr, Iran b Depertment of Physics, Masjed-Soleiman Branch, Islamic Azad University (I.A.U), Masjed-Soleiman, Iran c Department of Physics, Ahwaz Branch, Islamic Azad University, Ahwaz, Iran d Nanotechnology Laboratory, Esfarayen University, North Khorasan, Iran e Low Dimensional Materials Research Center, Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia Received 13 August 2013; received in revised form 21 August 2013; accepted 22 August 2013 Available online 30 August 2013 Abstract Undoped and group-I elements doped ZnO nanowires were synthesized using a thermal evaporation method. Field emission scanning electron microscopy (FESEM) results showed that, the undoped ZnO nanowires were ultra-long with uniform diameters. On the other hand, the length of the doped ZnO nanowires was in the range of some hundred of nanometers. X-ray diffraction (XRD) patterns clearly indicated hexagonal structures for all of the products. X-ray photoelectron spectroscopy (XPS) studies confirmed the oxidation states of Li, Na, K, in the ZnO lattice. An asymmetric O 1s peak indicated the presence of oxygen in an oxide layer. The effect of doping on the optical band-gap and crystalline quality was also investigated using photoluminescence (PL), UV–vis, and Raman spectrometers. The Raman spectra of the products indicated a strong E 2 (high) peak. The PL spectra exhibited a strong peak in the ultraviolet (UV) region of the electromagnetic spectrum for all of the ZnO nanowires. The UV peak of the doped ZnO nanowires was red-shifted compared to the undoped ZnO nanowires. In addition, the UV–vis spectra of the samples showed similar results compared to the PL results. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Films; C. Optical properties; D. ZnO 1. Introduction Zinc oxide (ZnO) is an n-type metal oxide semiconductor with a wide band-gap (3.36 eV) and large exciton binding energy (60 meV) at room temperature. These characteristics make this material interesting for many applications such as solar cells [1], field emission materials [2], nano-electronic devices [3], gas sensor [4], and photocatalyst properties [5]. The key factors affecting these applications are the shape, size, impurities, doping, structures, and phases. For this reason, many researchers in recent years have focused on the synthesis of doped and undoped nanocrystalline materials such as ZnO. In addition to ours, many other groups have also reported the synthesis of doped ZnO nanostructures with various morphologies using different methods [6–9]. However, the key challenge that needs to be overcome for the realization of most ZnO based applications is the fabrication of p-type material. p-type ZnO may be achieved by the substitution of group-I elements on the Zn-site [10–12] and group-V elements on the O-site [13–15], respectively. Although many attempts has been made recently over the material conductivity type is still to be obtained and hence a comprehensive investigation of the fundamental proper- ties of acceptors in ZnO is needed. From literature survey it is found that, the selected element from group-I elements showed better properties as dopants materials than group-V elements in terms of the shallowness of the acceptor level [16]. Therefore, the study of different effects of group-I as dopants on structural and optical properties of ZnO nanostructures can lead to obtain p-type ZnO nanostructures. Several groups have tried to synthesize p-type ZnO nanos- tructures by employing group-I elements as acceptors. Recently, p-type Li-doped ZnO nanowires have been grown by our group, which were grown by a thermal evaporation method. It was observed that not only lithium could play as an acceptor in ZnO structures but also could improve the optical properties of the www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.08.100 n Corresponding author. Tel.: þ98 916 6224993; fax: þ 98 681 3330093. E-mail address: Yousefi.ramin@gmail.com (R. Yousefi).