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DF: Fachverband Dielektrische Festkörper
DF 9: Electric, Electromechanical and Optical Properties I
DF 9.3: Talk
Thursday, March 29, 2007, 11:00–11:20, H48
Polaronic charge transport in reduced LiNbO3 investigated by means of time-resolved ESA spectroscopy — •Christoph Merschjann, Bettina Schoke, Daniela Conradi, Mirco Imlau, and Manfred Wöhlecke — Department of Physics, University of Osnabrück, D-49069 Osnabrück
Charge-transport processes are investigated in differently reduced LiNbO3 single crystals by means of time-resolved excited-state-absorption (ESA) spectroscopy. The detected transient light-induced absorption (αli) upon intense pulsed laser illumination (λ = 532 nm, τ = 8 ns) originates from four distinct types of metastable small polarons. From the temporal and spectral characteristics of αli one is able to distinguish between bound NbLi4+ and free NbNb4+ polarons, NbLi4+:NbNb4+ bipolarons, and bound O− hole polarons. Among other results we find competing photochromic effects in the blue spectral range in reduced LiNbO3. Furthermore, non-exponential relaxations of αli are observed, whose time constants strongly depend on the state of reduction and purity of the samples. The excitation and recombination phenomena of photo-induced small polarons can be described by a charge transport model, based on a random-walk of excited charge carriers. The presented experimental method is an ideal complement to EPR and electrical measurements, yielding time-resolved spectra at room temperature.
Supported by the Deutsche Forschungsgemeinschaft (projects IM 37/2-2 and TFB 13-04).