Low-Temperature Synthesis of Magic-Sized CdSe Nanoclusters: Influence of Ligands on Nanocluster Growth and Photophysical Properties

We present a low-temperature (68-70 degrees 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 similar to 1.8 nm. Powder Xray diffraction analysis showed a sharp peak at low angle (2 theta = 5.3 degrees), 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 trioctylarnine-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.