Photoluminescent Colloidal Nanohelices Self-Assembled from CdSe Magic-Size Clusters via Nanoplatelets

Abstract

Reports on photoluminescent colloidal semiconductor two-dimensional (2D) helical nanostructures with one-dimensional quantum confinement are relatively rare. Here, we discuss the formation of such photoluminescent nanostructures for CdSe. We show that when as-synthesized unpurified zero-dimensional (0D) CdSe magic-size clusters (MSCs) (passivated by carboxylate ligands with three-dimensional quantum confinement) are dispersed in a solvent (such as toluene or chloroform) containing hexadecylamine and then subjected to sonication, helical nanostructures are obtained, as observed by transmission electron microscopy. We demonstrate that the formation involves the self-assembly of 0D MSCs into 2D nanoplatelets, which act as intermediates. The CdSe MSCs and their self-assembled 2D nanostructures display almost identical static optical properties, namely, a sharp absorption doublet with peaks at 433 and 460 nm and a narrow emission peak at 465 nm; this is a subject for further study. This study introduces new methods for fabricating photoluminescent helical nanostructures via the self-assembly of photoluminescent MSCs.

Magic‐Sized Stoichiometric II–VI Nanoclusters

“…The magic‐sized CdSe and its related nanoclusters have been identified to be metastable precursor clusters that have been implicated in nanocrystal nucleation, transforming into various colloidal nanocrystals, such as quantum wires, nanosheets, nanorods, nanoribbons, nanohelices, nanodisks, and nanoplatelets. [ 16,62,102–106 ] Hyeon et al. [ 13 ] proposed the initial formation of a metal‐salt primary‐amine bilayer 2D template followed by lamellar structures as the predominant path for the CdSe nanosheet synthesis.…”

Reversible Transformation between CsPbBr3 Perovskite Nanowires and Nanorods with Polarized Optoelectronic Properties

“…Similarly, very small Stokes shift can be found in atom-scale-uniform magic sized quantum dots or 2D quantum materials with magic thickness. [61,62] The spectra of CsPbBr 3 nanorods also can be tuned by the halide ion exchange, with the nanorod morphology retained. The ion exchange prepared CsPbCl x Br 3-x and CsPbBr x I 3-x nanorods have decreased and increased diameters compared with the starting CsPbBr 3 nanorods, respectively, consistent with the crystal lattice change (Figures S1 and S6, Supporting Information).…”

“…Similarly, very small Stokes shift can be found in atom‐scale‐uniform magic sized quantum dots or 2D quantum materials with magic thickness. [ 61,62 ]…”

Magic-sized CdSe nanoclusters: a review on synthesis, properties and white light potential

“…It was observed that the obtained mass spectra exhibited more peaks than the spectra obtained for CdSe and ZnSe, which had only one prominent peak. 171,172 Single singularity in the resulting cluster was also observed as different sized cluster contribution was not present. It was also interpreted that these alloy clusters were formed by integrating zinc atoms instead of similar cadmium atoms or vice-versa.…”

“…Energy transfer from host band state of semiconductor to states of Mn 2+ was confirmed on the basis of photoluminescence emission (PLE) spectrum, making it obvious that the manganese ions were present in a Cd 2+ site. 171 Laser desorption/ionization time-of-flight mass spectroscopy was employed for characterizing the prepared clusters. It was observed that the obtained mass spectra exhibited more peaks than the spectra obtained for CdSe and ZnSe, which had only one prominent peak.…”