title: Nano-engineered electron-hole exchange interaction controls exciton dynamics in core-shell semiconductor nanocrystals.
abstract: 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. 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. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. 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. In thick-shell samples, the EI energy reduces to <250 μeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron-hole overlap.
authors.affiliation: Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: S
authors.initials: S
authors.lastname: Brovelli
authors.forename: R D
authors.initials: RD
authors.lastname: Schaller
authors.forename: S A
authors.initials: SA
authors.lastname: Crooker
authors.forename: F
authors.initials: F
authors.lastname: García-Santamaría
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: R
authors.initials: R
authors.lastname: Viswanatha
authors.forename: J A
authors.initials: JA
authors.lastname: Hollingsworth
authors.forename: H
authors.initials: H
authors.lastname: Htoon
authors.forename: V I
authors.initials: VI
authors.lastname: Klimov
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry; D002616:Chemical Engineering / Q000379:methods; D004574:Electromagnetic Fields; D004583:Electrons; D005453:Fluorescence; D046529:Microscopy, Electron, Transmission; D008962:Models, Theoretical; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry; D013696:Temperature
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide