Colloidal CdTe Nano Crystals Synthesis and Characterization

Report No. ARL-TR-4584
Authors: Fred Semendy, Gomatam Jaganathan, Nibir Dhar, Sudhir Trivedi, Ishwara Bhat,
Date/Pages: September 2008; 16 pages
Abstract: Synthesis of CdTe nano crystals (NCs) in uniform sizes and in good quality was performed in our nano lab and further characterized by absorption spectra, photoluminescence (PL), and atomic force microscopy (AFM). In this growth procedure, CdTe nano crystal band gap is strongly dependent on the growth time and not on the injection temperature or organic ligand concentration. This is very attractive because the nano crystal size can be easily controlled by the growth time only and is very attractive for large scale synthesis. The color of the solution changes from greenish yellow to light orange, then to deep orange and finally grayish black to black over a period of one hour. This is a clear indication of the gradual growth of different size (and different band gap) of CdTe nano crystals as a function of the growth time. In other words, the size of the nano crystal and its band gap can be controlled by adjusting the growth time after injection of the tellurium. The prepared CdTe NCs were characterized by absorption spectra, photoluminescence (PL), AFM and X-ray diffraction. Measured absorption maxima are at 521, 560, 600, and 603 nm corresponding to band gaps of 2.38, 2.21, and 2,07 eV respectively for growth times of 15, 30, 45, and 60 minutes. From the absorption data, nano crystal growth size saturates out after 45 minutes. AFM scanning of these materials indicate that the size of these particles is between 4 to 10 nm in diameter for the growth time of 45 minutes. This report presents growth and characterization data on CdTe nano crystals for various growth times.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2008