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DF: Fachverband Dielektrische Festkörper

DF 9: Electric, Electromechanical and Optical Properties I

DF 9.5: Vortrag

Donnerstag, 29. März 2007, 11:40–12:00, H48

Comparison of the light-induced absorption in single-domain LiNbO₃ and PPLN:Y after thermal reduction in vacuum — •Bettina Schoke¹, Christoph Merschjann¹, Mirco Imlau¹, and Inna Naumova² — ¹Department of Physics, University of Osnabrück, Germany — ²Physics Department, Moscow State University, Russia

We study excitation and recombination processes of small polarons in nominally pure single-domain and yttrium doped periodically poled LiNbO₃ (PPLN:Y) after the samples were thermally reduced in vacuum. This treatment creates bipolarons (Nb_Li⁴⁺:Nb_Nb⁴⁺) which are stable at room temperature. They may be dissociated into small bound (Nb_Li⁴⁺) and free (Nb_Nb⁴⁺) polarons via light illumination (”optical gating”). The resulting light-induced absorption is measured time–resolved via excited–state–absorption (ESA) spectroscopy in the blue, red and infrared spectral range after optical excitation with intense ns laser pulses (λ = 532 nm). In thermally reduced PPLN:Y, as in single-domain LiNbO₃, we observe both dissociation and recombination of bipolarons. The investigations also indicate the existence of photo-induced hole polarons (O⁻) at room temperature. From the direct comparison of both samples we can deduce the influence of the periodic poling on the charge transport of the small polarons and can clarify the role of the yttrium in LiNbO₃ with regard to the polaronic properties. Financial support by the DFG (projects TFB 13-04, IM 37/2-2 and GRK695).