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

Abstract

For those colloidal semiconductor CdSe nanospecies that exhibit sharp optical absorption doublets, different explanations have appeared in the literature regarding their morphological nature and formation, with no consensus reached. Here, we discuss the transformation pathway in two types of CdSe nanoplatelets (NPLs), from NPL-393 to NPL-460, exhibiting absorption doublets at 373/393 and 433/460 nm, respectively. Synchrotronbased small/wide-angle X-ray scattering (SAXS/WAXS) was performed to monitor the in situ transformation associated with the temperature. Combining the results of SAXS/WAXS, optical spectroscopy, and transmission electron microscopy, we propose that the transformation pathway experiences corresponding magic-sized clusters (MSCs), which display similar optical properties but with zero-dimensional structure. From stacked NPL-393 to stacked NPL-460, the transformation goes through sequentially individual NPL-393, MSC-393, MSC-460, and individual NPL-460 at their corresponding characteristic temperature. The present findings provide compelling evidence that both MSCs and their assembled NPLs exhibit similar optical absorption.

Direct and Indirect Pathways of CdTeSe Magic-Size Cluster Isomerization Induced by Surface Ligands at Room Temperature

“…For example, a continuous red-shift behavior is expected when zero-dimension (0D) QDs grow in size due to monomer addition directly onto the mother QDs . On the other hand when a stepwise red-shift is observed, monomer addition has often been assumed to take place on CdSe 0D clusters to become larger or 2D nanoplatelets (NPLs) to become thicker. ,,− This assumption infers that the intermediate does not have a measurable optical absorption, but it is difficult to understand why now. The difficulty disappears, however, when this assumption is abandoned and the concept of the PC-assisted transformation is applied.…”

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).…”

“…Synchrotron-based SAXS is an effective tool for probing nanoscale size. ,,,− To explore further the pathway of the formation of CdTeS MSC-381 from the binary IP samples, we performed in situ synchrotron-based SAXS with a data collection interval of 3 min. The same unified model was used to fit the SAXS data. ,− During the incubation from 0 to 30 min, the change of the overall size obtained is presented in Figure , with open circular symbols for the CdTe PC/MSC in the binary CdTe sample and with open triangular symbols for the CdTeS PC/MSC in the mixture of the two binary IP samples. The corresponding SAXS profiles collected are shown in (a, b) of Figure S6.…”

Direct and Indirect Evolution of Photoluminescent Semiconductor CdS Magic‐Size Clusters through Their Precursor Compounds

“…We suggest that the evolution of the CdS NPLs is due to the self-assembly of the CdS MSCs, similar to that suggested for CdSe (Figure S1-8A). [14,23] For the formation and transformation of PL semiconductor 2D NPLs, the PC-related (Figure S1-8A) and not PC-related (Figure S1-8B) pathways have been proposed; the present study does not address this ongoing issue.…”