A Two‐Pathway Model for the Evolution of Colloidal Compound Semiconductor Quantum Dots and Magic‐Size Clusters

Abstract

A fundamental understanding of formation pathways is critical to the controlled synthesis of colloidal semiconductor nanocrystals. As ultrasmall‐size quantum dots (QDs) sometimes emerge in reactions along with magic‐size clusters (MSCs), distinguishing their individual pathway of evolution is important, but has proven difficult. To decouple the evolution of QDs and MSCs, an unconventional, selective approach has been developed, along with a two‐pathway model that provides a fundamental understanding of production selectivity. For on‐demand production of either ultrasmall QDs or MSCs, the key enabler is in how to allow a reaction to proceed in the time prior to nucleation and growth of QDs. In this prenucleation stage, an intermediate compound forms, which is the precursor compound (PC) to the MSC. Here, the two‐pathway model and the manipulation of such PCs to synthesize either ultrasmall QDs or binary and ternary MSCs are highlighted. The two‐pathway model will assist the development of nucleation theory as well as provide a basis for a mechanism‐enabled design and predictive synthesis of functional nanomaterials.

Room-Temperature Evolution of Ternary CdTeS Magic-Size Clusters Exhibiting Sharp Absorption Peaking at 381 nm

“…Then, they were mixed at room temperature; CdTeSe MSC-399 developed during the room-temperature incubation of the resultant mixture. We suggested that similar to binary MSCs, − ternary CdTeSe MSC-399 also evolved from its counterpart PC, ternary CdTeSe PC-399, and PC-399 was produced via the substitution reaction of the CdTe PC and CdSe Mo/Fr . During the mixture incubation, PC-399 formed with a relatively fast rate and then transformed to MSC-399 at a relatively slow speed.…”

“…Colloidal II–VI metal (M) and chalcogenide (E) semiconductor magic-size clusters (MSCs) have their own special precursor compounds (PCs). − While MSCs display sharp optical absorption at constant wavelengths, their counterpart PCs are transparent at these and longer wavelengths. The idea that MSCs evolve from their corresponding PCs via intramolecular reorganization is present in the two-pathway model that provides an in-depth understanding of the growth relation between binary ME MSCs and binary colloidal semiconductor ME quantum dots (QDs) (Scheme S1a).…”

“…The idea that MSCs evolve from their corresponding PCs via intramolecular reorganization is present in the twopathway model that provides an in-depth understanding of the growth relation between binary ME MSCs and binary colloidal semiconductor ME quantum dots (QDs) (Scheme S1a). 4 This model suggests that prior to nucleation and growth of binary ME QDs, the self-assembly of M and E precursors occurs followed by the formation of M−E covalent bonds inside each assembly. Accordingly, the binary ME PC is produced.…”

Room-temperature formation of alloy ZnxCd13−xSe13 magic-size clusters via cation exchange in diamine solution

“…Since the first report of CdS magic-size clusters (MSCs) by Henglein and his co-workers in the reaction of Cd(ClO 4 ) 2 and H 2 S in 1984, 1 MSCs composed of discrete numbers of atoms have also been found to exist in the pre-nucleation stage of quantum dots (QDs). 2–7 Colloidal MSCs are considered to be crucial in describing how nanomaterials evolve from molecules and nanocrystals, 8–12 and they are commonly employed as precursors for preparing functional nanomaterials, such as QDs, 13,14 nanowires, 15 nanosheets, 16–18 nanorods 19 and nanoribbons. 18–21 Moreover, MSCs also demonstrate their potential applications in single-component white-light emitters 22–26 and ultrasmall colloidal dilute magnetic semiconductors.…”

Transformation Pathway from CdSe Nanoplatelets with Absorption Doublets at 373/393 nm to Nanoplatelets at 434/460 nm

“…Furthermore, it has been proposed that dMSC-393 and dMSC-460 have their corresponding precursor compounds (PCs), and PC-393 is formed in reactions first. The PCs and their counterpart MSCs have similar core masses, while the former is optically transparent; their transformations are reversible via intramolecular reorganizations. − For the transformation from CdSe dMSC-393 to dMSC-460, a PC-enabled pathway has been proposed, which involves three key steps. dMSC-393 transforms first to PC-393.…”