Dresden 2014 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Nanoparticles and Composite Materials

CPP 41.2: Talk

Thursday, April 3, 2014, 09:45–10:00, ZEU 222

Simulation of disorder effects in the optical spectra of homogeneously alloyed CdSeS nanocrystals — •Daniel Mourad¹, Tangi Aubert², Antoine Guille², Edouard Brainis², and Zeger Hens² — ¹Institut für Theoretische Physik, Universität Bremen — ²Physics and Chemistry of Nanostructures, Ghent University

Monodisperse, homogeneously alloyed CdSe(x)S(1−x) nanocrystals, which can be grown by means of colloidal synthesis, allow for a gradual tayloring of the absorption/emission properties by variation of the composition. Besides the nonlinear variation of the excitation gap as a function of x ("bowing"), the optical spectra also show an additional alloy-only feature on the S-rich side. The homogeneity of the alloying could be confirmed by Raman spectroscopy [Aubert et al., Chem. Mater. 25(12), 2388 (2013)].

Starting from a tight-binding model for the constituents CdSe and CdS, we try to understand the electronic and optical properties of this quantum dot ensemble system in theory. In our approach alloy effects are simulated exact in the disorder, i.e. the single-particle energies and wave functions are calculated for a large (N≈50) number of nanocrystals in a stochastical approach for each concentration x. Then, dipole and Coulomb matrix elements are calculated for each realization in order to obtain the light-matter coupling and the many-body properties of this system within the configuration interaction method [Mourad and Czycholl, Eur. Phys. J. B 78, 497 (2010)]. It is shown that alloying relaxes the selection rules that apply to pure CdSe and CdS and the relation between simulation and experimental results is discussed.