ARTICLE Copyright © 2014 by American Scientific Publishers All rights reserved. Printed in the United States of America Science of Advanced Materials Vol. 6, pp. 1–7, 2014 (www.aspbs.com/sam) Large-Scale Synthesis of Highly Pure Novel Cadmium Semi-Spheres and Their Anomalous Optical Properties Muhammad Arshad Kamran † , Ruibin Liu † , Li-Jie Shi, and Bingsuo Zou * Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing 100081, China ABSTRACT Highly pure and large-scale novel cadmium (Cd) semi-spheres were prepared via Chemical Vapor Deposi- tion (CVD). The growth process is described with multi-steps of Vapor-Liquid-Solid (VLS) and decomposition of CdS nanostructure in Ar(90%) + H 2 (10%) mixture gas stream at definite temperature and selected zone. In contrast to previous Cd nanostructures, our individual Cd semi-spheres show strong room-temperature pho- toluminescence (PL) at around 591 nm, which is detected for the first time. Its long lived (>∼ 1.5 ns) electronic state by time-resolved PL supports the origin of strong emission, which is attributed to radiative recombina- tion of electrons in the s, p conduction band near the Fermi surface and the holes at the d-bands or local microstructures generated by UV-visible laser excitation. It is a plasmonic band as that in Au, Ag, Cu tuned by sizes. Strong surface enhanced Raman scattering (SERS) of pyridine species have been detected from this Cd semi-sphere, as strong as the silver metals does for SERS agents. The above optical responses has strong relation to their growth process and as formed microstructures in one sphere. It reflects that such Cd spheres may be a much cheaper candidates for applications in LEDs and other optoelectronic devices, for example, the plasmonic enhanced solar cells. KEYWORDS: Chemical Vapor Deposition, Cadmium, Metals, Photoluminescence, Silver. 1. INTRODUCTION As an important silver white metal in group II-B, Cad- mium (Cd) finds a great deal of applications such as barrier in nuclear reactors because of their tendency to absorb low energy neutrons. 1 Cd or its alloy bars are used to control the fission process in the nuclear reactors. Cd has many industrial uses as it is used in telluride solar panels, 2 rechargeable nickel-cadmium batteries, yel- low/red pigments, insoluble in inorganic solvents, water and coatings (electroplating). 3 4 It also used as a pre- cursor material for fabrication of Cd based semiconduc- tors such as cadmium oxide (CdO), 5 6 cadmium sulfide (CdS), 7 8 cadmium selenide (CdSe) 9 10 and cadmium tel- luride (CdTe) 11 12 etc. Only few reports are available in literature on the synthesis and structure studies of Cd metal nanostructures. 1 4 13 14 Except, one paper, 15 no one even have studied the strong luminescence properties of Cd nano/micro-structure. Considering that the plasmon bring ∗ Author to whom correspondence should be addressed. Email: zoubs@bit.edu.cn † These two authors contributed equally to this work. Received: xx xx xxxx Accepted: xx xx xxxx a dramatic change of photonics, maybe Cd also show inter- esting properties like Au and Ag nanostructures because they are very close in the Periodic Table. But it did not show strong plasmonic oscillation in the literature. This can be understood by our synthesis as they may have relations to their plasmonic behaviors. Therefore, investi- gations on the controllable growth of Cd metal and explor- ing its optical properties, we suggest Cd metal spheres is important candidate in various field. Optically excited metal surfaces show no or very little luminescence owing to its lacking of bandgap. First obser- vation of optically excited radiation from the metal sur- faces of Au and Cu was reported by Mooradian in 1969. 16 Mooradian attributed this radiation to the recombination of the electrons in the s , p conduction band near the Fermi surface and the holes in the d-bands generated by optical excitation. Spatially structural irregularity facilitates this transition process. The observation of interband radiative recombination in metals may provide another technique to investigate the band structure of metals as well as to determine the nature of scattering mechanisms of localized excited electrons and holes. In the presented work, we report the large-scale fabri- cation of highly pure metallic novel semi-spheres of Cd Sci. Adv. Mater. 2014, Vol. 6, No. xx 1947-2935/2014/6/001/007 doi:10.1166/sam.2014.1981 1