Formation of Size-Tunable and Nearly Monodisperse InP Nanocrystals: Chemical Reactions and Controlled Synthesis

Formation of InP quantum dots (QDs) in a non-coordinating solvent is divided into four stages for studying the chemical reactions. By introducing tertiary phosphines, such as trioctylphosphine (TOP), in the first stage, the four stages are all altered significantly, which enables the formation of InP QDs with high optical quality, that is, with a well-defined first-exciton absorption peak and a high-energy absorption shoulder in their ultraviolet–visible spectra. The first stage is the formation of a less sterically hindered complex with three monodentate carboxylates and one TOP ligand [In(TOP)(St)3] by reacting indium stearate [In(St)3] with TOP, which is soluble and reactive at room temperature. The second stage is the formation of InP clusters with near-unity yield and very small size by reacting In(TOP)(St)3 with tris(trimethylsilyl)phosphine [(TMS)3P] at ambient temperatures (20–50 °C). During the third stage, tiny InP clusters formed with the In(TOP)(St)3 precursor enable the formation of nearly monodisperse InP QDs by a hot-injection approach. In the following fourth stage, the InP QDs formed in the third stage grow further in the same pot by the secondary injections of the InP clusters—the ones formed at ambient temperatures with the In(TOP)(St)3 precursor for efficient "self-focusing of size distribution"—to finally obtain high-quality InP QDs with their absorption peak covering most part of the visible window (between ∼480 and 660 nm).