Journal
ACS NANO
Volume 14, Issue 4, Pages 4206-4215Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.9b09147
Keywords
nanoplatelets; ternary architecture; photoluminescence; k.p calculations; fluorescence upconversion
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Funding
- Ministero degli Affari Esteri e della Cooperazione Internazionale
- Ministry of Science, Technology and Space of the state of Israel [IONX-NC4SOL]
- Crown Photonics Center of the Weizmann Institute of Science
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program [714876 PHOCONA]
- MINECO [CTQ2017-83781-P]
- UJI [B2017-59]
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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.
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