5 research outputs found
Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules
Coupled colloidal quantum dot molecules (CQDMs) are an emerging class of nanomaterials, manifesting two coupled emission centers and thus introducing additional degrees of freedom for designing quantum-dot-based technologies. The properties of multiply excited states in these CQDMs are crucial to their performance as quantum light emitters, but they cannot be fully resolved by existing spectroscopic techniques. Here we study the characteristics of biexcitonic species, which represent a rich landscape of different configurations essentially categorized as either segregated or localized biexciton states. To this end, we introduce an extension of Heralded Spectroscopy to resolve the different biexciton species in the prototypical CdSe/CdS CQDM system. By comparing CQDMs with single quantum dots and with nonfused quantum dot pairs, we uncover the coexistence and interplay of two distinct biexciton species: A fast-decaying, strongly interacting biexciton species, analogous to biexcitons in single quantum dots, and a long-lived, weakly interacting species corresponding to two nearly independent excitons. The two biexciton types are consistent with numerical simulations, assigning the strongly interacting species to two excitons localized at one side of the quantum dot molecule and the weakly interacting species to excitons segregated to the two quantum dot molecule sides. This deeper understanding of multiply excited states in coupled quantum dot molecules can support the rational design of tunable single- or multiple-photon quantum emitters.U.B. and D.O. acknowledge the support of the Israel Science Foundation (ISF) and the Directorate for Defense Research and Development (DDR&D), grant No. 3415/21. J.I.C. and J.P. acknowledge support from UJI project B-2021-06. E.S., A.L., Y.E.P., and Y.O. acknowledge support from the Hebrew University Center for Nanoscience and Nanotechnology
Ligands Mediate Anion Exchange between Colloidal Lead-Halide Perovskite Nanocrystals
The soft lattice of lead-halide perovskite nanocrystals (NCs) allows tuning their optoelectronic characteristics via anion exchange by introducing halide salts to a solution of perovskite NCs. Similarly, cross-anion exchange can occur upon mixing NCs of different perovskite halides. This process, though, is detrimental for applications requiring perovskite NCs with different halides in close proximity. We study the effects of various stabilizing surface ligands on the kinetics of the cross-anion exchange reaction, comparing zwitterionic and ionic ligands. The kinetic analysis, inspired by the "cage effect" for solution reactions, showcases a mechanism where the surface capping ligands act as anion carriers that diffuse to the NC surface, forming an encounter pair enclosed by the surrounding ligands that initiates the anion exchange process. The zwitterionic ligands considerably slow down the cross-anion exchange process, and while they do not fully inhibit it, they confer improved stability alongside enhanced solubility relevant for various applications.ISSN:1530-6984ISSN:1530-699
Electric field induced color switching in colloidal quantum dot molecules at room temperature
Colloidal semiconductor quantum dots are robust emitters implemented in
numerous prototype and commercial optoelectronic devices. However, active
fluorescence color tuning, achieved so far by electric-field induced Stark
effect, has been limited to a small spectral range, and accompanied by
intensity reduction due to the electron-hole charge separation effect.
Utilizing quantum dot molecules that manifest two coupled emission centers, we
present a novel electric-field induced instantaneous color switching effect.
Reversible emission color switching without intensity loss is achieved on a
single particle level, as corroborated by correlated electron microscopy
imaging. Simulations establish that this is due to the electron wavefunction
toggling between the two centers dictated by the electric-field and affected by
the coupling strength. The quantum dot molecules manifesting two coupled
emission centers may be tailored to emit distinct colors, opening the path for
sensitive field sensing and color switchable devices such as a novel pixel
design for displays or an electric field color tunable single photon source.Comment: Manuscript: 27 pages, 6 figures, Supplementary: 38 page
Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules
Coupled colloidal quantum dot molecules are an emerging class of
nanomaterials, introducing new degrees of freedom for designing quantum
dot-based technologies. The properties of multiply excited states in these
materials are crucial to their performance as quantum light emitters but cannot
be fully resolved by existing spectroscopic techniques. Here we study the
characteristics of biexcitonic species, which represent a rich landscape of
different configurations, such as segregated and localized biexciton states. To
this end, we introduce an extension of Heralded Spectroscopy to resolve
different biexciton species in the prototypical CdSe/CdS coupled quantum dot
dimer system. We uncover the coexistence and interplay of two distinct
biexciton species: A fast-decaying, strongly-interacting biexciton species,
analogous to biexcitons in single quantum dots, and a long-lived,
weakly-interacting species corresponding to two nearly-independent excitons
separated to the two sides of the coupled quantum dot pair. The two biexciton
types are consistent with numerical simulations, assigning the
strongly-interacting species to two excitons localized at one side of the
quantum dot molecule and the weakly-interacting species to excitons segregated
to the two quantum dot molecule sides. This deeper understanding of multiply
excited states in coupled quantum dot molecules can support the rational design
of tunable single- or multiple-photon quantum emitters.Comment: 13 pages, 5 figure