Article pubs.acs.org/JPCC
One- and Two-Photon Absorption in CdS Nanodots and Wires: The Role of Dimensionality in the One- and Two-Photon Luminescence Excitation Spectrum Alexander W. Achtstein,*,‡ Ana Ballester,∥ Jose L. Movilla,∥ Jonas Hennig,‡,† Juan I. Climente,∥ Anatol Prudnikau,# Artsiom Antanovich,# Riccardo Scott,‡ Mikhail V. Artemyev,# Josep Planelles,∥ and Ulrike Woggon‡ ‡
Institute of Optics and Atomic Physics, Technical University of Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany Departament de Quimica Fisicai Analitica, Universitat Jaume I, Castelló de la Plana 12080, Spain # Institute for Physico-Chemical Problems, Belarusian State University, 220030 Minsk, Belarus ∥
S Supporting Information *
ABSTRACT: We investigate the spectral dependence of the linear and two-photon absorption of wurtzite CdS nanoparticles (dots and rods) by means of quantitative one- and two-photon photoluminescence excitation spectroscopy and effective mass theory modeling. Absolute two-photon absorption cross sections free from spectrally varying beam related uncertainties are obtained by means of a new reference dyebased method. The two-photon spectrum features of rods strongly differ from those of dots, due to the distinct energy structure of quasi-one-dimensional systems. The transversal confinement is found to dominate the energy of the absorption maxima while the longitudinal one dominates their absorption intensity. This suggests two-photon transition energy and intensity can be controlled independently in nanorods. For both geometries we observe a sizable spectral shift between the first one- and two-photon absorption maxima, which we conclude is inherent to the small rates of near-bandgap two-photon transitions rather than to the particular geometry of the absorber. The provided understanding of the spectral dependence of the two-photon absorption of CdS dots and rods is of strong interest for the design of nanocrystals with optimized two-photon absorption properties for bioimaging and phototherapy applications.
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through confinement.5 However, intense laser excitation is required to achieve substantial absorption. Therefore, it is necessary to find stable two-photon absorbers with high absorption cross sections and photoluminescence (PL) quantum yield to reduce the necessary excitation densities. As compared to standard organic dyes having rather low TPA cross sections (
