Two-Dimensional CdSe-PbSe Heterostructures and PbSe Nanoplatelets: Formation, Atomic Structure, and Optical Properties

Abstract

Cation exchange enables the preparation of nanocrystals (NCs), which are not reachable by direct synthesis methods. In this work, we applied Pb 2+ -for-Cd 2+ cation exchange on CdSe nanoplatelets (NPLs) to prepare two-dimensional CdSe-PbSe heterostructures and PbSe NPLs. Lowering the reaction temperature slowed down the rate of cation exchange, making it possible to characterize the intermediary NCs ex situ with atomically resolved high-angle annular dark-field scanning transmission electron microscopy and optical spectroscopy. We observe that the Pb 2+ -for-Cd 2+ cation exchange starts from the vertices of the NPLs and grows into the zinc blende CdSe (zb-CdSe) lattice as a rock salt PbSe phase (rs-PbSe), while the anion (selenium) sublattice is being preserved. In agreement with previous works on CdTe-PbTe films, the interfaces between zb-CdSe and rs-PbSe consist of shared {001} and {011} planes. The final PbSe NPLs are highly crystalline and contain protrusions at the edges, which are slightly rotated, indicating an atomic reconfiguration of material. The growth of PbSe domains into CdSe NPLs could also be monitored by the emission peak shift as a function of the exchange time. Temperature-dependent emission measurements confirm a size-dependent change of the band gap energy with temperature and reveal a strong influence of the anisotropic shape. Time-resolved photoluminescence measurements between 4 and 30 K show a dark-bright exciton-state splitting different from PbSe QDs with three-dimensional quantum confinement.

Toward Bright Colloidal Near-Infrared Emitters: Surface Passivation of 2D PbSe Nanoplatelets by Metal Halides

“…However, accessing NPLs with highly efficient PL in the NIR is a synthetic challenge. For example, NIR-emitting PbSe NPLs have been synthesized by oriented attachment of PbSe NCs and by cation exchange of CdSe NPLs. , Additionally, more elaborate NIR-active systems such as CdSe–PbSe heterostructures and HgX NCs on HgX NPLs (X = Se or Te) have been realized via cation exchange from Cd-based NPLs. However, only few direct syntheses have yielded PbSe NPLs up to now. , A recent example from our group is the direct synthesis of colloidal PbSe NPLs from lead oleate and selenourea at 0 °C, reaching a PLQY of 37.4% at 1.27 eV (980 nm) …”

Regiospecific Cation Exchange in Nanocrystals and Its Potential in Diversifying the Nanostructural Library

“…The physicochemical properties of NCs can be finely tuned by their composition, size/shape, and heterointerfaces, making them promising candidate materials for many applications. [13][14][15][16][17][18] Ion exchange on the various template NCs available has been proposed as a promising strategy for heterostructured nanoparticle synthesis and attracted tremendous interest. [7,9,11] This section mainly discusses fundamental principles and experimental insights into the rules of CERs for developing NCs.…”

“…Zinc blende CdSe and rock salt PbSe had three similar anion sublattices of (001), (011), and (001), which led to the formation of more complex heterostructures (Figure 5C). [ 16 ] This CER principle has been expanded and studied as a methodology to control regiospecificity. [ 46,47 ] The influence of different crystal structures of the reacting platform on the diffusive abilities of cations was reported by Gariano et al in the case of cation exchange between Cu 2 Se NCs and Pb 2+ .…”

“…The regiospecific cation exchange of Pb 2+ for Cd 2+ , starting at the vertical facets of CdSe nanoplatelets, was revealed through the crystallographic study of intermediate reaction products. [ 16 ] The emission from the PbSe domains was indicated by the strong redshifted broad PL peak at 1.33 eV in the emission spectrum (Figure 9C). A dark–bright exciton‐state splitting was present in PbSe nanoplatelets with 3D quantum confinement.…”

“…C) Schematic depictions of heterostructures from zinc blende-CdSe and rock salt-PbSe with a continuous anion (selenium) sublattice (black spheres). Reproduced with permission [16]. Copyright 2022, American Chemical Society.…”