Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 13: Colloidal and Nanoparticles
CPP 13.12: Talk
Tuesday, February 26, 2008, 18:00–18:15, C 264
Femtosecond Spectroscopy Study of the Exciton Relaxation Dynamics in Silicon Quantum Dots — •Carola Kryschi1, Volker Kuntermann1, Carla Cimpean1, and Dietrich Haarer2 — 1Institut für Physikalische Chemie I, FAU, Egerlandstr. 3, D-91058 Erlangen — 2BIMF, Universität Bayreuth, D-95440 Bayreuth
This contribution is targeted to the development of surface-modified silicon quantum dots (Siqdots) with tailored luminescence properties. The surface modification of Siqdots with sizes between 1 and 5 nm has been successfully achieved via two different synthesis routes, first, by controlled oxidation followed from silanization and second, by thermal hydrosilylation with chromophores. The luminescence properties of ethanolic Siqdots dispersions were characterized using stationary and time-resolved luminescence spectroscopy techniques, whereas the ultrashort exciton relaxation dynamics were examined using femtosecond transient absorption spectroscopy. Silanized Siqdots were observed to exhibit two species of photoluminescence (PL): the blue emission at 380 nm is assigned to localized surface states, whereas radiative recombination of quantum confined excitons gives rise to a broad PL band around 800 nm. Whereas the latter is ascribed to Siqdots with sizes larger than 3 nm, for Siqdots smaller than 1.5 nm exciton relaxation dynamics is understood to occur predominantly by trapping due to lower-lying surface states which may radiatively decay. Siqdots terminated with suited chromophores were observed to exhibit only one PL band in the visible that is ascribed to exciton states involving resonant couplings to the conjugated electron system of the chromophores.