Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules

Abstract

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.

Lateral Confinement in 2D Nanoplatelets: A Strategy to Expand the Colloidal Quantum Engineering Toolbox

“…A weakly interacting biexciton is then formed, as in homodimer CdSe/CdS double quantum dots. [42] As the lateral confinement of the CdSe crown is relaxed, the NPL evolves toward the limit of a CdSe--only NPL, where attractive biexcitons have been confirmed both experimentally [43] and theoretically. [44] As the power is increased, we observe a saturation of the PL signal magnitude (Figure 4b), which suggests the appearance of new non-radiative pathways likely resulting from Auger recombination.…”

Adaptive optical imaging with entangled photons

“…For instance, spatially variant aberrations will restrict the field of view in the corrected image, although this limitation might be circumvented by using alternative AO designs such as conjugate and multiconjugate AO ( 35 , 36 ). Finally, it is important to note that QAO is not yet adaptable in fluorescence microscopy, but this could change in the future with the emergence of biomarkers that emit photon pairs ( 37 ).…”