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

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.