Sensors and Actuators B 138 (2009) 304–309 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb ZnS and DDT (dodacanthiol-1) capping in CdSe nanoparticles Radheshyam Rai a,∗ , Abhilasha Srivastava b , Kiran Jain c a Indian Institute of Technology, Department of Physics, Hauz Khas, New Delhi 110016, India b Honeywell Technology Solution Lab, Bangalore, India c Electronic Materials Division, Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India article info Article history: Received 19 November 2008 Received in revised form 23 January 2009 Accepted 30 January 2009 Available online 6 March 2009 Keywords: CdSe nanoparticles ZnS Dodecanethiol Photoluminescence Optical band gap abstract CdSe nanoparticles were prepared by reverse micelle technique. Optical absorption and luminescence studies were carried out for samples prepared for different water to surfactant ratio. The prepared nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis absorption and photoluminescence (PL) spectra. The XRD analysis showed that the starch capped CdSe nanoparticles were of the hexagonal structure, the average particle size was calculated to be about 3nm according to the Debye–Scherer equation. Transmission electron microscopy (TEM) shows forma- tion of CdSe nanowire for CdSe NPs synthesized at water to surfactant ratio of 10. ZnS and dodecanethiol-1 (DDT) capping were used to passivate the surface of CdSe particles. The optical properties showed a red shift in the band gap for the capped material. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Nanoparticles have been investigated intensively in last many years, because of their size dependant properties and arrangement manner in nanosize. Exciton radius from the small-bore semi- conductor nanoparticles exhibit unique optical properties of the electron excitations because of confinement. The optical absorp- tion and emission can be tuned across the visible spectrum by changing the size of the nanoparticles making these materials attractive for applications in optoelectronics and nonlinear appli- cations [1,2]. CdSe is a promising photovoltaic material because of its high absorption coefficient and nearly optimum band gap energy for the efficient absorption and conversion. CdSe bulk has 1.74eV band gap and Bohr radii is 11.4nm [3]. CdSe nanoparticles have attracted considerable attention owing to their great potential applications in electrical and optoelectronic devices, and biological labeling. Surface atoms of the nanoparticles are bound by weaker forces because of missing neighbors, which leads to high surface activity. They act as trapped state for the photo-generated charges. Many efforts have been made to overcome this problem, including the passivating nanoparticles with organic or inorganic layers [4]. Capping CdSe nanoparticles (NPs) with a shell of another semicon- ductor of larger energy band gap, such as ZnS or CdS leads to a large improvement of the room temperature photoluminescence quan- ∗ Corresponding author. Tel.: +91 351 962782932; fax: +91 351 234425300. E-mail address: radheshyamrai@ua.pt (R. Rai). tum yield and the photo stability of such core–shell NPs is much larger than that of organic dyes [5,6]. CdSe nanoparticles have been prepared from various techniques such as chemical bath deposition, electrodeposition, laser ablation, vacuum deposition and reverse micelle techniques. Among various preparation techniques, reverse micelle and micro-emulsions have proved to be efficient in providing soft colloidal templates for con- trolling the size and shape of inorganic nanoparticles [7–10]. The reverse micelles are nanometer-sized droplets of water encased by a surfactant and suspended in oil. The reverse micelles have been used to synthesize size-controlled inorganic crystallites by carry- ing out aqueous chemical reactions (co-precipitation or reduction) in the water droplets. The reverse micelles restrict the growth of the particle and prevent aggregation. The most often used reverse micelle system is the aerosol OT (AOT)/H 2 O isooctane system. AOT has a negatively charged polar head and two non-polar tails. Isooc- tane has a structure similar to the tail structure of AOT and thus has the best penetration into AOT tails [11]. Kortan et al. demon- strated the mono-dispersity and core–shell structure of CdSe/CdS nanocrystals through reverse micelle technique [12]. CdSe/CdS NPs prepared through reverse micelle technique showed both higher band edge luminescence yield and greater stability under light illu- mination [13]. In the present work, we report the results of our investigations towards CdSe nanoparticle synthesis by the reverse micelle meth- ods. CdSe of different sizes were prepared by varying the water to surfactant ratio (W 0 ). The optical properties of prepared CdSe nanoparticles were studied in detail. A blue shift in the optical band gap was observed even for W 0 = 30. Further the results of 0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2009.01.074