Comprehensive Route to the Formation of Alloy Interface in Core/Shell Colloidal Quantum Dots

The electronic properties of colloidal quantum dots (CQDs) have shown intriguing potential in recent years for implementation in various optoelectronic applications. However, their chemical and photochemical stabilities, mainly derived from surface properties, have remained a major concern. This paper reports a new strategic route for the synthesis of surface-treated CQDs, the CdSe/CdS core/shell heterostructures, based on low-temperature coating of a shell constituent, followed by a programmed annealing process. A comprehensive follow-up of the stability and the optical properties through the various synthesis stages is reported, suggesting that the low-temperature coating is responsible for the formation of a sharp interface between the core and the shell, whereas a postcoating annealing process leads to the generation of a thin alloy interfacial layer. At the end of the process, the CdSe/CdS CQDs show a significant improvement of the photoluminescence quantum yield, as well as an exceptional photostability. Consequently, the work reported here provides a convenient generic route to the formation of core/shell CQDs to be employed as a procedure for achieving various other heterostructures

Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals

Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl₂, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn²⁺ by Cd²⁺ at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd²⁺ ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs