Low-Temperature Synthesis of Magic-Sized CdSe Nanoclusters: Influence of Ligands on Nanocluster Growth and Photophysical Properties John C. Newton, †,∥ Karthik Ramasamy, †,∥,⊥ Manik Mandal, ‡ Gayatri K. Joshi, † Amar Kumbhar, § and Rajesh Sardar* ,† † Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202, United States ‡ Department of Chemistry, Lehigh University, Seeley Mudd Building, 6 East Packer Avenue, Bethlehem, Pennsylvania 18015, United States § Chapel Hill Analytical and Nanofabrication Laboratory, University of North Carolina, Chapel Hill, North Carolina 27599, United States * S Supporting Information ABSTRACT: We present a low-temperature (68−70 °C) synthesis of green light-emitting, trioctylphosphine oxide-capped magic-sized CdSe nanoclusters from the reaction of trioctylphosphine oxide−cadmium acetate precursors with trioctylphosphine selenide. We observed continuous growth of these magic-sized nanoclusters, which displayed a first absorption peak at 422 nm and broad luminescence covering the entire visible region. The diameter of the nanoclusters determined by transmission electron microscopic measurement was ∼1.8 nm. Powder X- ray diffraction analysis showed a sharp peak at low angle (2θ = 5.3°), confirming the formation of ultrasmall, magic-sized nanoclusters. The nanocluster formation was also studied using different purities of trioctylphosphine oxide. The synthetic protocol was extended to the preparation of oleylamine-, ethylphosphonic acid-, lauric acid-, and trioctylamine-stabilized magic-sized CdSe nanoclusters. Importantly, the investigation showed that the nature of the cadmium precursors plays a crucial role in the nanocluster growth mechanism. The applicability of the trioctylphosphine oxide-capped nanoclusters was further investigated through a ligand exchange reaction with oleylamine, which displayed an extremely narrow absorption peak at 415 nm (full width at half-maximum of 14 nm) and a band edge emission peak at 456 nm with a shoulder at 438 nm. ■ INTRODUCTION Since the discovery of the “hot injection” method of monodispersed semiconductor nanclusters (SCNCs) synthesis by Murray, Norris, and Bawendi, 1 numerous synthetic protocols have been developed to produce clusters with 2.0 nm diameter. 2−9 SCNCs with diameter below 2.0 nm are an important class of nanomaterials because, depending on the surface passivating ligands, these particles display either broad luminesence or a combination of band edge and broad luminesence. Such dual emission characteristics are ideal photophysical properties for fabrication of optoelectronic devices as well as bridge nanoparticles and molecular clusters 8−12 Moreover, SCNCs with sizes below 2 nm display a unique stability due to their specific atomic composition and structure. Indeed, this unique stability is largely attributed to the cluster-cage structure of the NC, which assemble in particular sizes [(CdSe) n , n = 13, 19, 33, and 34] producing “magic-sized” NCs. Several methods have been developed for synthesizing magic-sized CdSe NCs. 2,13−22 Peng et al. 7 were the first to report a high-temperature method for the preparation of magic- sized CdSe NCs, where a mixture of tributylphosphine selenide and trioctylphosphine (TOP) in toluene was injected at 320 °C into a mixture of cadmium oxide, trioctylphosphine oxide (TOPO), and tetradecylphosphonic acid. The NCs displayed a sharp absorption peak at 349 nm, which is a known characteristic of NCs containing 17 Cd atoms. 8 Kasuya and co-workers synthesized magic-sized CdSe NCs using a low- temperature reverse micelle protocol, where an aqueous solution of Na 2 SeSO 3 was added to a Cd−decylamine complex in toluene. 20 They revealed the chemical composition of magic- sized NCs by mass spectroscopy and X-ray diffraction measurements and defined the NC compositions as (CdSe) 33 Received: September 8, 2011 Revised: January 26, 2012 Article pubs.acs.org/JPCC © XXXX American Chemical Society A dx.doi.org/10.1021/jp2086818 | J. Phys. Chem. C XXXX, XXX, XXX−XXX