Berlin 2008 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 9: Poster
DF 9.13: Poster
Dienstag, 26. Februar 2008, 15:00–18:00, Poster G
Influence of Mg-doping on the lifetime of optically generated small polarons in LiNbO3 — •Daniela Conradi1, Bettina Schoke1, Christoph Merschjann1, Mirco Imlau1, Gabor Corradi2, and Katalin Polgár2 — 1Fachbereich Physik, Universität Osnabrück, Osnabrück, Germany — 2Hungarian Academy of Sciences, Budapest, Hungary
Excitation and recombination of optically generated small electron and hole polarons in Mg-doped LiNbO3 is investigated by means of time-resolved excited-state-absorption (ESA) spectroscopy. Transient light-induced absportion changes αli(t) are observed in the visible and near infrared spectral range upon excitation with intense green laser pulses (λ = 532 nm, τ = 8 ns, Ip ≤ 1400 GW/m2). The results indicate the generation of bound small O− hole polarons and bound small NbLi4+ electron polarons in LiNbO3:Mg with doping concentrations below the optical-damage-resistance threshold. In contrast, for concentrations above this threshold the light-induced absorption is caused by hole polarons and free small NbNb4+ electron polarons. In either case the characteristics of αli(t) in the blue-green spectral range point to the presence of further extrinsic impurities — most likely Fe2+/3+.
We present a model concerning all these types of polarons for LiNbO3 doped with Mg below and above the optical-damage-resistance threshold. The influence of additional extrinsic impurities on the excitation and recombination of the small polarons is discussed.
Supported by the Deutsche Forschungsgemeinschaft (Projects IM 37/2-2 and TFB 13-04).