title: Towards understanding the unusual photoluminescence intensity variation of ultrasmall colloidal PbS quantum dots with the formation of a thin CdS shell.
abstract: In this study, we report anomalous size-dependent photoluminescence (PL) intensity variation of PbS quantum dots (QDs) with the formation of a thin CdS shell via a microwave-assisted cation exchange approach. Thin shell formation has been established as an effective strategy for increasing the PL of QDs. Nonetheless, herein we observed an unusual PL decrease in ultrasmall QDs upon shell formation. We attempted to understand this abnormal phenomenon from the perspective of trap density variation and the probability of electrons and holes reaching surface defects. To this end, the quantum yield (QY) and PL lifetime (on the ns-μs time scales) of pristine PbS QDs and PbS/CdS core/shell QDs were measured and the radiative and non-radiative recombination rates were derived and compared. Moreover, transient absorption (TA) analysis (on the fs-ns time scale) was performed to better understand exciton dynamics at early times that lead to and affect longer time dynamics and optical properties such as PL. These experimental results, in conjunction with theoretical calculations of electron and hole wave functions, provide a complete picture of the photophysics governing the core/shell system. A model was proposed to explain the size-dependent optical and dynamic properties observed.
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Ren
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA. zhang@ucsc.edu.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Lindley
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Haiguang
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Long
authors.initials: L
authors.lastname: Tan
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Belete Atomsa
authors.initials: BA
authors.lastname: Gonfa
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA. zhang@ucsc.edu.
authors.forename: Ying-Chih
authors.initials: YC
authors.lastname: Pu
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, Quebec H3A 0C3, Canada.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Liu
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: François
authors.initials: F
authors.lastname: Vidal
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA. zhang@ucsc.edu.
authors.forename: Jin Z
authors.initials: JZ
authors.lastname: Zhang
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca and Centre for Self-Assembled Chemical Structures, McGill University, Montreal, Quebec H3A 2K6, Canada.
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Vetrone
authors.affiliation: Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Univerisité du Québec, 1650 Boul. Lionel-Boulet, Varennes, Québec J3X 1S2, Canada. ma@emt.inrs.ca.
authors.forename: Dongling
authors.initials: D
authors.lastname: Ma