Berlin 2008 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 7: Point defect spectroscopy and engeneering

DF 7.5: Vortrag

Dienstag, 26. Februar 2008, 12:00–12:20, EB 107

Influence of extrinsic defects on the recombination behavior of light-induced hole and electron polarons in KNbO₃ — •Bettina Schoke, Christoph Merschjann, Stefan Torbrügge, and Mirco Imlau — Department of Physics, University of Osnabrück, Germany

We study excitation and recombination processes of small hole and electron polarons in nominally pure and iron doped KNbO₃ samples by means of time–resolved excited–state–absorption (ESA) spectroscopy. The light–induced absorption α_li(t) in the visible and infrared spectral–range is measured after optical excitation with intense ns laser pulses (λ = 532 nm ,τ = 8 ns). In nominally pure KNbO₃ we observe the formation and relaxation of free (Nb_Nb⁴⁺) electron polarons and bound O⁻ hole polarons within a single decay of α_li after a two–photon process of excitation. Their mutual recombination via incoherent hopping transport is crucially accelerated by Iron doping which additionally causes a slow decay component in KNbO₃:Fe. The reduction of the polaron hopping transport length in Fe-doped samples can be attributed to the increased number densities of optically-generated O⁻ hole polarons by additional one-quantum excitations due to extrinsic defects.

Financial support by the Deutsche Forschungsgemeinschaft DFG (TFB 13-04, IM 37/2-2, GRK 695).