Regensburg 1998 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 6: Poster

DF 6.9: Poster

Donnerstag, 26. März 1998, 09:30–12:30, A

Dynamics of the light-induced NIR-absorption of Nb⁴⁺ polarons in SBN:Cr and SBN:Ce crystals at low temperature — •M. Gao¹, S. Porcher¹, R. Pankrath¹, V. Vikhnin², and S. Kapphan¹ — ¹FB Physik, Universität Osnabrück, 49069 Osnabrück — ²Ioffe Institute, 194021 St. Petersburg, Russia

Sr_xBa_1−xNb₂O₆ ( congruent x=0.61 ) crystals show enhanced photorefractive properties with doping impurities like Ce, Cr, Rh. Under Kr⁺-laser light and Ar⁺-laser light at low temperature SBN:Cr and SBN:Ce crystals show a broad polaron absorption band in the NIR. A theoretical model is proposed to describe the charge transport process in doped SBN crystals: electrons are excited by illumination from Cr³⁺/Ce³⁺ to the conduction band and some of them will be trapped by Nb⁵⁺ to form Nb⁴⁺ polarons; at the same time hole polarons can be generated by the illumination as well; electrons trapped in Nb⁴⁺ polarons can directly tunnel or hop the potential barrier to recombine with Cr⁴⁺/Ce⁴⁺ or hop away to other trapping centers or recombine with hole polarons. The steady-state of the polaron concentration during the illumination and the decay kinetics after the laser is switched off are calculated based on the model. The experimental intensity dependence, temperature dependence and non-exponential decay process of the light-induced Nb⁴⁺ polaron quantitatively fit with the expectation of this model.

This work is supported by DFG (SFB225, C7), NATO HTECHLG-960540 and DFG436RUS113/341/1(R).