Quenching dynamics in CdSe nanoparticles: surface-induced defects upon dilution

Lucia Hartmann (1) , Abhishek Kumar (2) , Matthias Welker (3) , Angela Fiore (1) , Carine Julien-Rabant (2) , Marina Gromova (4) , Michel Bardet (5) , Peter Reiss (1) , Paul N W Baxter (3) , Frédéric Chandezon (1) , Robert Bernard Pansu (6, 2)

1 SPRAM - UMR 5819 - Structures et propriétés d'architectures moléculaire
2 PPSM - Photophysique et Photochimie Supramoléculaires et Macromoléculaires
3 ICS - Institut Charles Sadron
4 INAC - Institut Nanosciences et Cryogénie
5 SCIB - UMR E3 - Service de Chimie Inorganique et Biologique
6 IDA - Institut d'Alembert

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.

Mots clés: Fluorescence dynamics; quantum dot; binomial distribution; ligand adsorption; Blumen_Klafter Law; CdSe

Domaines: Chimie théorique et/ou physique

Lucia Hartmann, Abhishek Kumar, Matthias Welker, Angela Fiore, Carine Julien-Rabant, et al.. Quenching dynamics in CdSe nanoparticles: surface-induced defects upon dilution. ACS Nano, 2012, 6 (10), pp.9033-41. ⟨10.1021/nn303150j⟩. ⟨hal-00751942⟩