CdSe/CdS/CdTe Core/Barrier/Crown Nanoplatelets: Synthesis, Optoelectronic Properties, and Multiphoton Fluorescence Upconversion

Abstract

Colloidal two-dimensional (2D) nanoplatelet heterostructures are particularly interesting as they combine strong confinement of excitons in 2D materials with a wide range of possible semiconductor junctions due to a template-free, solution-based growth. Here, we present the synthesis of a ternary 2D architecture consisting of a core of CdSe, laterally encapsulated by a type-I barrier of CdS, and finally a type-II outer layer of CdTe as so-called crown. The CdS acts as a tunneling barrier between CdSe- and CdTe-localized hole states, and through strain at the CdS/CdTe interface, it can induce a shallow electron barrier for CdTe-localized electrons as well. Consequently, next to an extended fluorescence lifetime, the barrier also yields emission from CdSe and CdTe direct transitions. The core/barrier/crown configuration further enables two-photon fluorescence upconversion and, due to a high nonlinear absorption cross section, even allows to upconvert three near-infrared photons into a single green photon. These results demonstrate the capability of 2D heterostructured nanoplatelets to combine weak and strong confinement regimes to engineer their optoelectronic properties.

Surface Modification of CdE (E: S, Se, and Te) Nanoplatelets to Reach Thicker Nanoplatelets and Homostructures with Confinement-Induced Intraparticle Type I Energy Level Alignment

“…1 For the latter, fine engineering of the band alignment enables localization of the exciton in different areas of the NPLs as well as high quantum yield efficiency from green to red with NPLs that can even exhibit multicolour emission. [14][15][16][17][18][19] Such NPLs are suitable for low threshold lasing or light concentrators. 15,20,21 In the zinc blende NPLs, the thickness is oriented along the [001] direction, 22,23 with an alternation of cadmium and chalcogenide planes, completed by cadmium planes on both sides (CdE NPLs, with E:S, Se, Te; of N MLs present, N planes of E and N+1 planes of Cd).…”

Light-Emitting Diodes Based on Two-Dimensional Nanoplatelets

“…The electrons and holes are spatially separated between the core and the crown, and redshifted PL emission can be observed. Recently, a ternary heterostructure of CdSe/CdS/CdTe core/barrier/crown nanoplatelets was reported [82]. Here, CdSe NPL is a core, CdS is a type I barrier, and CdTe is a crown.…”

Tunable Quantum Photoinitiators for Radical Photopolymerization

“…The charge carriers effectively control the concentration of oxidative species generated and also retard the annihilating function of the oxygen species. Quantum PIs are also used for two-photon (2P) absorption-based printing approaches [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. In addition, 2P polymerization processes involve the use of femtosecond laser radiation at a wavelength below the bandgap to excite the quantum PI.…”