Ag + is an emerging electronic dopant in III–V and II–VI nanostructures, introducing intragap electronic states optically coupled to the host conduction band. « lessĮlectronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Magneto-optical measurements indicate that the V S are not magnetically coupled to the NC bands and that the polarization properties are determined by the spin of the valence-band photohole, whose spin flip is massively slowed down due to suppressed exchange interaction with the donor-localized electron. V S-localized electrons are almost unaffected by trapping, and suppression of more » thermal quenching boosts the emission efficiency to 85%. Here, we produce a model system for donor-bound excitons in CdSeS NCs engineered with sulfur vacancies (V S) that introduce a donor state below the conduction band (CB), resulting in long-lived intragap luminescence. To date, the opposite donor-bound exciton scheme has not been realized because of the unavailability of suitable donor dopants. One compelling example is II–VI NCs incorporating heterovalent coinage metals in which hole capture produces acceptor-bound excitons. « lessĬontrolled insertion of electronic states within the band gap of semiconductor nanocrystals (NCs) is a powerful tool for tuning their physical properties. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. Nanocrystals where the valence-band maximum is derived from the bulk B band have a 'quasi-bright' ground-state exciton. Nanocrystals where more » the valence-band maximum originates from the bulk A band have a 'dark' ground-state exciton. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Chemical Sciences, Geosciences & Biosciences Division OSTI Identifier: 1623850 Grant/Contract Number: AC52-06NA25396 2009LANL1096 Resource Type: Accepted Manuscript Journal Name: Nature Communications Additional Journal Information: Journal Volume: 2 Journal Issue: 1 Journal ID: ISSN 2041-1723 Publisher: Nature Publishing Group Country of Publication: United States Language: English Subject: 14 SOLAR ENERGY 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY 77 NANOSCIENCE AND NANOTECHNOLOGY Nanoparticles Nanoscience and technology Optical physics Quantum = , (LANL), Los Alamos, NM (United States) Sponsoring Org.: USDOE Laboratory Directed Research and Development (LDRD) Program USDOE Office of Science (SC), Basic Energy Sciences (BES). Publication Date: Tue Apr 19 00:00: Research Org.: Los Alamos National Lab. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron–hole overlap. In thick-shell samples, the EI energy reduces to <250µeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300K and magnetic fields up to 7T. We show that the dark– bright splitting can be widely tuned by controlling the electron–hole spatial overlap in core– shell CdSe/CdS NCs with a variable shell width. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. This dark–bright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. A strong electron–hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active (‘bright’) and optically passive (‘dark’) excitons.
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