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

Abstract

We present a low-temperature (68–70 °C) synthesis\nof green light-emitting, trioctylphosphine oxide-capped magic-sized\nCdSe nanoclusters from the reaction of trioctylphosphine oxide–cadmium\nacetate precursors with trioctylphosphine selenide. We observed continuous\ngrowth of these magic-sized nanoclusters, which displayed a first\nabsorption peak at 422 nm and broad luminescence covering the entire\nvisible region. The diameter of the nanoclusters determined by transmission\nelectron microscopic measurement was ∼1.8 nm. Powder X-ray\ndiffraction analysis showed a sharp peak at low angle (2θ =\n5.3°), confirming the formation of ultrasmall, magic-sized nanoclusters.\nThe nanocluster formation was also studied using different purities\nof trioctylphosphine oxide. The synthetic protocol was extended to\nthe preparation of oleylamine-, ethylphosphonic acid-, lauric acid-,\nand trioctylamine-stabilized magic-sized CdSe nanoclusters. Importantly,\nthe investigation showed that the nature of the cadmium precursors\nplays a crucial role in the nanocluster growth mechanism. The applicability\nof the trioctylphosphine oxide-capped nanoclusters was further investigated\nthrough a ligand exchange reaction with oleylamine, which displayed\nan extremely narrow absorption peak at 415 nm (full width at half-maximum\nof 14 nm) and a band edge emission peak at 456 nm with a shoulder\nat 438 nm.