Abstract
Controlled insertion of electronic states within the band gap of semiconductor nanocrystals (NCs) is a powerful tool for tuning their physical properties. One compelling example is II–VI NCs incorporating heterovalent coinage metals in which hole capture produces acceptor-bound excitons. To date, the opposite donor-bound exciton scheme has not been realized because of the unavailability of suitable donor dopants. Here, we produce a model system for donor-bound excitons in CdSeS NCs engineered with sulfur vacancies (VS) that introduce a donor state below the conduction band (CB), resulting in long-lived intragap luminescence. VS-localized electrons are almost unaffected by trapping, and suppression of thermal quenching boosts the emission efficiency to 85%. Magneto-optical measurements indicate that the VS 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.
Highlights
Controlled insertion of electronic states within the band gap of semiconductor nanocrystals (NCs) is a powerful tool for tuning their physical properties
Nano Letters pubs.acs.org/NanoLett model system adopting a vacancy engineering strategy that exploits the propensity of metal sulfides to present sulfur vacancies eV below t(hVeS)CtBh.a29t−i3n1trModourceespaelcoificaclaizlleyd, CledvSelbpuilnkncerdysatablosuatnd[1] colloidal particles have been shown to emit self-activated intragap luminescence emerging from a Lambe-Klick mechanism[32] where sulfur vacancies act as donors[33] following the reaction VS ⇌ VS+ + eC−B with the Fermi energy for the first ionization being located ∼700 meV below the conduction band (CB)
Ultrafast capture of eC−B by VS+ temporarily reduces them to VS0 centers that can either decay nonradiatively or recombine with the valence band (VB) photohole producing the characteristic intragap luminescence.[29−31] This makes NCs with sulfur vacancies interesting model systems to explore the implications of donor states in the optical and magneto-optical properties of NCs, possibly suggesting strategies to introduce new functionalities by design
Summary
Controlled insertion of electronic states within the band gap of semiconductor nanocrystals (NCs) is a powerful tool for tuning their physical properties.
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