# Berlin 2008 – wissenschaftliches Programm

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# DF: Fachverband Dielektrische Festkörper

## DF 14: Electric, electromechanical and optical properties II

### DF 14.1: Vortrag

### Donnerstag, 28. Februar 2008, 14:00–14:20, EB 407

**Consequences of hopping charge transport for the relaxation of light-induced absorption in oxide crystals** — •Christoph Merschjann, Bettina Schoke, and Mirco Imlau — Fachbereich Physik, Universität Osnabrück, D-49069 Osnabrück

Transient light-induced absorption changes α_{li}(*t*) are observed in various nonlinear optical oxide crystals as, e.g., LiNbO_{3}, KNbO_{3}, KTiOPO_{4}, and β-BaB_{2}O_{4}.
In contrast to basic assumptions the decay shape of α_{li}(*t*) in these materials is generally not monoexponential.
A fairly good — though empirical — description of the temporal evolution of the light-induced absorption is given by stretched exponential functions: α_{li}(*t*) = α_{li}^{(0)} · exp[−(*t*/τ)^{β}], with 0 < β ≤ 1.
However, the origin of this peculiar behavior is still unclear.
One possible reason may be a random-walk hopping transport of excited charge carriers, as predicted by the theory for small polarons in oxide crystals.

We present random-walk simulations of both band and hopping charge transport with different complexities.
The results indicate that hopping transport is more likely to lead to the observed effects than classical band transport.
The connection between transport models and mathematical descriptions of α_{li}(*t*) is discussed.

Supported by the Deutsche Forschungsgemeinschaft (Projects IM 37/2-2, TFB 13-04, and GRK 695).