title: Two Photon Absorption in II-VI Semiconductors: The Influence of Dimensionality and Size.
abstract: We report a comprehensive study on the two-photon absorption cross sections of colloidal CdSe nanoplatelets, -rods, and -dots of different sizes by the means of z-scan and two-photon excitation spectroscopy. Platelets combine large particle volumes with ultra strong confinement. In contrast to weakly confined nanocrystals, the TPA cross sections of CdSe nanoplatelets scale superlinearly with volume (V(∼2)) and show ten times more efficient two-photon absorption than nanorods or dots. This unexpectedly strong shape dependence goes well beyond the effect of local fields. The larger the particles' aspect ratio, the greater is the confinement related electronic contribution to the increased two-photon absorption. Both electronic confinement and local field effects favor the platelets and make them unique two-photon absorbers with outstanding cross sections of up to 10(7) GM, the largest ever reported for (colloidal) semiconductor nanocrystals and ideally suited for two-photon imaging and nonlinear optoelectronics. The obtained results are confirmed by two independent techniques as well as a new self-referencing method.
authors.affiliation: †Institute of Optics and Atomic Physics, Technical University of Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Scott
authors.affiliation: †Institute of Optics and Atomic Physics, Technical University of Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Achtstein
authors.affiliation: ‡Institute for Physico-Chemical Problems, Belarusian State University, 220030 Minsk, Belarus.
authors.forename: Anatol
authors.initials: A
authors.lastname: Prudnikau
authors.affiliation: ‡Institute for Physico-Chemical Problems, Belarusian State University, 220030 Minsk, Belarus.
authors.forename: Artsiom
authors.initials: A
authors.lastname: Antanovich
authors.affiliation: §Istituto Italiano di Tecnologia, Via Morego 30, IT-16163 Genova, Italy.|∥Department of Physics, University of Genoa, Via Dodecaneso 33, 16146 Genova, Italy.
authors.forename: Sotirios
authors.initials: S
authors.lastname: Christodoulou
authors.affiliation: §Istituto Italiano di Tecnologia, Via Morego 30, IT-16163 Genova, Italy.
authors.forename: Iwan
authors.initials: I
authors.lastname: Moreels
authors.affiliation: ‡Institute for Physico-Chemical Problems, Belarusian State University, 220030 Minsk, Belarus.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Artemyev
authors.affiliation: †Institute of Optics and Atomic Physics, Technical University of Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Woggon
keywords: CdSe; Two-photon absorption; local field; nanoplatelets; nanorods; quantum dots