title: Design and synthesis of heterostructured quantum dots with dual emission in the visible and infrared.
abstract: The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR)-active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intraband relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from the CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogeneous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe and the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.
authors.affiliation: Center for Advanced Solar Photophysics, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Qianglu
authors.initials: Q
authors.lastname: Lin
authors.forename: Nikolay S
authors.initials: NS
authors.lastname: Makarov
authors.forename: Weon-kyu
authors.initials: WK
authors.lastname: Koh
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Velizhanin
authors.forename: Claudiu M
authors.initials: CM
authors.lastname: Cirloganu
authors.forename: Hongmei
authors.initials: H
authors.lastname: Luo
authors.forename: Victor I
authors.initials: VI
authors.lastname: Klimov
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Pietryga
keywords: cation exchange; core/shell nanocrystal; dual emission; effective-mass model; quantum dots; vacancy formation