4 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
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The Effect of Monomer Size on Fusion and Coupling in Colloidal Quantum Dot Molecules.
The fusion step in the formation of colloidal quantum dot molecules, constructed from two core/shell quantum dots, dictates the coupling strength and hence their properties and enriched functionalities compared to monomers. Herein, studying the monomer size effect on fusion and coupling, we observe a linear relation of the fusion temperature with the inverse nanocrystal radius. This trend, similar to that in nanocrystal melting, emphasizes the role of the surface energy. The suggested fusion mechanism involves intraparticle ripening where atoms diffuse to the reactive connecting neck region. Moreover, the effect of monomer size and neck filling on the degree of electronic coupling is studied by combined atomistic-pseudopotential calculations and optical measurements, uncovering strong coupling effects in small QD dimers, leading to significant optical changes. Understanding and controlling the fusion and hence coupling effect allows tailoring the optical properties of these nanoscale structures, with potential applications in photonic and quantum technologies
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