title: Alternating layer addition approach to CdSe/CdS core/shell quantum dots with near-unity quantum yield and high on-time fractions.
abstract: We report single-particle photoluminescence (PL) intermittency (blinking) with high on-time fractions in colloidal CdSe quantum dots (QD) with conformal CdS shells of 1.4 nm thickness, equivalent to approximately 4 CdS monolayers. All QDs observed displayed on-time fractions > 60% with the majority > 80%. The high-on-time-fraction blinking is accompanied by fluorescence quantum yields (QY) close to unity (up to 98% in an absolute QY measurement) when dispersed in organic solvents and a monoexponential ensemble photoluminescence (PL) decay lifetime. The CdS shell is formed in high synthetic yield using a modified selective ion layer adsorption and reaction (SILAR) technique that employs a silylated sulfur precursor. The CdS shell provides sufficient chemical and electronic passivation of the QD excited state to permit water solubilization with greater than 60% QY via ligand exchange with an imidazole-bearing hydrophilic polymer.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Greytak
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Allen
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Wenhao
authors.initials: W
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Young
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Zoran
authors.initials: Z
authors.lastname: Popović
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Walker
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts, USA.
authors.forename: Moungi G
authors.initials: MG
authors.lastname: Bawendi