Materials Science and Engineering B 137 (2007) 59–62 Luminescence property and large-scale production of ZnO nanowires by current heating deposition P. Singjai ∗ , T. Jintakosol, S. Singkarat, S. Choopun Department of Physics, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Received 14 June 2006; accepted 21 October 2006 Abstract Large-scale production for ZnO nanowires has been demonstrated by current heating deposition. Based on the use of a solid–vapor phase carbothermal sublimation technique, a ZnO–graphite mixed rod was placed between two copper bars and gradually heated by passing current through it under constant flowing of argon gas at atmospheric pressure. The product seen as white films deposited on the rod surface was separated for further characterizations. The results have shown mainly comb-like structures of ZnO nanowires in diameter ranging from 50 to 200 nm and length up to several tens micrometers. From optical testing, ionoluminescence spectra of as-grown and annealed samples have shown high green emission intensities centered at 510 nm. In contrast, the small UV peak centered at 390 nm was observed clearly in the as-grown sample which almost disappeared after the annealing treatment. © 2006 Elsevier B.V. All rights reserved. Keywords: Zinc oxides; Nanowires; Current heating deposition; Luminescence 1. Introduction ZnO nanostructures have been studied extensively in the past few years due to their fundamental and technological importance [1–5]. In particular, it is a wide-direct-band gap (∼3.37 eV) II-VI semiconductor with many potential applications such as nano- laser arrays [2,6], gas sensors [7–10], field emission devices [11,12] and luminescent materials [13–16]. Luminescence prop- erty of ZnO has been investigated by several excitation energy sources such as photoluminescence (PL) [13–16] and ionolu- minescence (IL) [17]. Generally, both UV and visible emissions have been observed due to the excitonic recombination and deep level emissions, respectively. In the later case, the visible emis- sions were attributed to interstitial zinc and oxygen vacancy defects [18]. However, improvements of the luminescence effi- ciency of ZnO have been recently investigated [14–16]. Up to now, many ZnO configurations have been reported such as nanobelts [1,17], nanowires (NWs) [10–13], nanoneedles [3], nanotetrapods [9] and nanocombs [19–22]. Furthermore, a review article written by Wang [4] has also suggested that ZnO nanostructures are probably the most abundant forms ∗ Corresponding author. Tel.: +66 53 941922x610; fax: +66 53 892271. E-mail address: singjai@chiangmai.ac.th (P. Singjai). of any known materials. Therefore, proper control processing parameters are essential for synthesis of various ZnO nanos- tructures. From a physical point of view, the synthesis methods for one-dimensional (1D) ZnO nanostructures are categorized into two groups, metal catalyst-assisted growth and catalyst-free growth which corresponded to vapor–liquid–solid (VLS) and vapor–solid (VS) mechanisms, respectively. Yi and co-workers suggested that the latter is better than the former in terms of no metal catalyst impurity [3]. In this contribution, we demonstrate a method for large-scale production of a comb-like structure of ZnO NWs by a current heating technique without using any metal catalyst under a rel- ative high reductive environment. This paper also shows strong and stable green emissions of the as-grown and annealed NWs. 2. Experimental details ZnO NWs were grown by the current heating method in which it was first developed by Singjai and co-workers to produce SiC nanofibers from a charcoal rod [23]. However, the apparatus in this present report has been developed to produce the NWs in large-scale production (Fig. 1). In brief, the raw material was a mixture of 60 wt.% C (Ultra “F” purity, Ultra Carbon Corpora- tion, USA) and 40 wt.% ZnO (purity 99.99%, Sigma–Aldrich) powders. It is noted that this weight ratio gives an optimum rod 0921-5107/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2006.10.018