title: Quenching dynamics in CdSe nanoparticles: surface-induced defects upon dilution.
abstract: We have analyzed the decays of the fluorescence of colloidal CdSe quantum dots (QDs) suspensions during dilution and titration by the ligands. A ligand shell made of a combination of trioctylphosphine (TOP), oleylamine (OA), and stearic acid (SA) stabilizes the as-synthesized QDs. The composition of the shell was analyzed and quantified using high resolution liquid state 1H nuclear magnetic resonance (NMR) spectroscopy. A quenching of the fluorescence of the QDs is observed upon removal of the ligands by diluting the stock solution of the QDs. The fluorescence is restored by the addition of TOP. We analyze the results by assuming a binomial distribution of quenchers among the QDs and predict a linear trend in the time-resolved fluorescence decays. We have used a nonparametric analysis to show that for our QDs, 3.0 ± 0.1 quenching sites per QD on average are revealed by the removal of TOP. We moreover show that the quenching rates of the quenching sites add up. The decay per quenching site can be compared with the decay at saturation of the dilution effect. This provides a value of 2.88 ± 0.02 for the number of quenchers per QD. We extract the quenching dynamics of one site. It appears to be a process with a distribution of rates that does not involve the ligands.
authors.affiliation: Laboratoire d'Electronique Moléculaire, Organique et Hybride (LEMOH), INAC/SPrAM UMR 5819 (CEA-CNRS-UJF), CEA Grenoble, 17, rue des Martyrs, F-38054 Grenoble, France.
authors.forename: Lucia
authors.initials: L
authors.lastname: Hartmann
authors.forename: Abhishek
authors.initials: A
authors.lastname: Kumar
authors.forename: Matthias
authors.initials: M
authors.lastname: Welker
authors.forename: Angela
authors.initials: A
authors.lastname: Fiore
authors.forename: Carine
authors.initials: C
authors.lastname: Julien-Rabant
authors.forename: Marina
authors.initials: M
authors.lastname: Gromova
authors.forename: Michel
authors.initials: M
authors.lastname: Bardet
authors.forename: Peter
authors.initials: P
authors.lastname: Reiss
authors.forename: Paul N W
authors.initials: PN
authors.lastname: Baxter
authors.forename: Frédéric
authors.initials: F
authors.lastname: Chandezon
authors.forename: Robert B
authors.initials: RB
authors.lastname: Pansu
mesh_terms: D016477:Artifacts; D019187:Cadmium Compounds / Q000737:chemistry*; D003198:Computer Simulation; D008422:Materials Testing; D008956:Models, Chemical; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; D012996:Solutions; C058667:cadmium selenide