Temperature-controlled synthesis and characterization of Bi 4 Ge 3 O 12 nanowires Dong Sub Kwak a , Yong Jung Kwon a , Han Gil Na a , Tran Van Khai a , Chongmu Lee b , Hyoun Woo Kim a,⇑ a Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Republic of Korea b School of Materials Science and Engineering, Inha University, Incheon 402-751, Republic of Korea highlights " Bi 4 Ge 3 O 12 nanowires are fabricated by heating a mixture of Bi and Ge powders. " Growth temperature affected the morphology, structure, and chemical compositions of nanowires. " Bi 4 Ge 3 O 12 nanowires exhibited a hysteresis loop, indicating ferromagnetic behavior. article info Article history: Received 21 November 2012 Received in revised form 8 February 2013 Accepted 11 February 2013 Available online 18 February 2013 Keywords: Bi 4 Ge 3 O 12 Nanowires Photoluminescence abstract Varying the heating temperature of a mixture of Bi and Ge powders, we have successfully prepared Bi 4 Ge 3 O 12 nanowires. The growth at 600 °C was mainly controlled via a vapor–liquid–solid process, whereas the growth at 800 °C was dominated by a vapor–solid mechanism. Although 600 °C-grown nanowires were amorphous, being comprised of Bi, Ge, O, and Au elements, the Bi and Au elements prev- alently resided in the tip, playing a catalytic role in the nanowire growth. For 800 °C-grown nanowires, both the stem and tip were mainly comprised of cubic Bi 4 (GeO 4 ) 3 phase with additional Bi 2 O 3 and GeO 2 phases. Photoluminescence spectrum of 800 °C-grown nanowires exhibited GeO 2 -related emission band, as well as Bi 4 Ge 3 O 12 -related ones. The magnetic measurements showed that the Bi 4 Ge 3 O 12 nano- wires exhibited a hysteresis loop, indicating ferromagnetic behavior. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Bismuth germanate (Bi 4 Ge 3 O 12 , BGO) has an eulytine-type cubic structure (space group I3d), consisting of a regular arrange- ment of GeO 4 tetrahedron and distorted BiO 6 octahedron [1,2]. It has several advantages including non-hygroscopicity, large absorp- tion coefficient, and high mechanical strength [3,4]. In addition, while exhibiting not only an intense luminescence at room temperature but also having an intense radiation hardness at high energy particle detection [5], BGO has received enormous attention as a scintillator for use in high-energy physics and nuclear medi- cine [6]. Furthermore, doping with 3d and 4d ions can change the light-induced, optical, and holographic properties of Bi 4 Ge 3 O 12 single crystals. In particular, ruthenium (Ru) doping makes BGO a potential candidate for thermoluminescence studies [7]. One-dimensional (1D) nanowires have a variety of advantages including large surface-to-volume ratio and linear/straight path for carriers, improving electronic, optical, magnetic, and sensor properties. Accordingly, by introducing 1D nanowires, scientists and engineers have resolved some of the long-standing technical problems that have challenged the bulk/thin film community [8]. Accordingly, 1D nanostructures of Bi 4 Ge 3 O 12 will have promis- ing application in a variety of areas, including optoelectronics, thermoluminescence, and as scintillators. For example, the high surface-to-volume ratio of nanowires will enhance optoelectronic and thermoluminescence properties. In addition, being similar to nanoparticles [9], the scintillator with nanowire structures, unlike a conventional screen with micro-crystalline phosphor, will exhibit different optical and structural properties in terms of luminescence and image resolution, and so on [9]. However, in spite of promising applications, there have been rare reports on nanostructures of Bi 4 Ge 3 O 12 , not to mention nano- wires. The only 1D structure reported so far is Bi 4 Ge 3 O 12 fibers with the diameter in the range of 55–290 lm, which was prepared by the micro-pulling-down technique [10]. In the present study, we have obtained Bi 4 Ge 3 O 12 nanowires suc- cessfully, by means of heating a mixture of Bi and Ge powders. We have investigated the effect of growth temperature on the structure, morphology, and growth mechanism of 1D nanostructures. We 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.02.033 ⇑ Corresponding author. Tel.: +82 10 8428 0883. E-mail address: hyounwoo@hanyang.ac.kr (H.W. Kim). Chemical Engineering Journal 222 (2013) 337–344 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej