The synthesis of ultra-small metal chalcogenides with uniform size and composition would expedite the advancement of semiconductor nanocrystals' applications in the field of nanoscience and nanoimaging and faster production of advanced photovoltaic devices. Three-dimensional modeling and DFT energy calculations of ultra-small (CdSe)n clusters (< 2 nm) predicted the well-defined and ultrastable  clusters composed of (CdSe)13, (CdSe)19, (CdSe)33 and (CdSe)34 with core cage structures (fullerene-like). These thermodynamically stable ensembles of atoms are often called �magic sizes� and are formed by closed shells of atoms providing uniformity in their chemical composition approaching that of small molecules. Preferential synthesis and isolation of single-sized nanocrystals is extremely crucial in order to understand their precise optical and electronic properties, and for the further improvement of nanoscale devices. We present here a simple and efficient method for synthesizing blue-light emitting single-sized (CdSe)34 nanocrystals at room temperature in gram scale. The preferential formation of (CdSe)34 nanocrystals was determined by laser desorption ionization mass spectroscopy (LDI-MS). The absorption spectrum of magic-sized (CdSe)34 nanocrystals featured a lowest energy transition at 418 nm with two additional higher energy transitions at 382 nm and 353 nm respectively. The nanocrystals displayed sharp band-edge emission in the blue-light region centered at 432 nm and a weak broad emission profile covering the entire visible region of the spectrum. High-resolution transmission electron microscopic (HRTEM) and powder X-ray (XRD) analysis confirms the nanocrystals are 1.5 nm in diameter with a wurtzite crystal structure. The fluorescence quantum yield of the synthesized (CdSe)34 nanocrystals was found to be 7.04% which is highest to date for these kind of ultra-small CdSe nanocrystals. A similar approach was utilized to synthesize a series of (CdSe)34 nanocrystals with varying surface ligands, and the roles of different Cd and Se precursors towards the �magic-sized� nanocrystal formation were investigated in details.

Role of stabilizing ligands and precursors on the formation of �magic-sized� ultrasmall (CdSe)<sub>34</sub> nanocrystals

246th National Meeting (2013)

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Role of stabilizing ligands and precursors on the formation of �magic-sized� ultrasmall (CdSe)34 nanocrystals

Role of stabilizing ligands and precursors on the formation of �magic-sized� ultrasmall (CdSe)₃₄ nanocrystals