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22 November 1999 Lifetime of polarons in lithium-niobate crystals
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Pulsed illumination of lithium-niobate crystals with green light excites electrons from deep traps into the intrinsic defect NbLi5+ (Nb on Li site in the valence state 5+) and creates NbLi4+ centers (small polarons). The electrons trapped in this more shallow center increase the light absorption in the red and near-infrared. The dark decay of the polaron concentration is observed by monitoring the relaxation of these absorption changes. Iron- doped lithium-niobate crystals with different concentrations of NbLi are investigated for various illumination conditions. The relaxation shows a stretched-exponential behavior which is in disagreement with the predictions of the standard rate-equation model. The observed lifetimes of the polarons range from tens of nanoseconds to some milliseconds. Computer simulations reveal that all results can be explained considering distance-dependent excitation and recombination rates, i.e. the lifetime of an individual polaron depends on the distance to the next available deep electron trap. Based on the new insights, tailoring of lithium-niobate crystals for non-volatile holographic storage becomes possible.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dirk Berben, Karsten Buse, S. Wevering, P. Herth, Theo Woike, and Eckhard Kratzig "Lifetime of polarons in lithium-niobate crystals", Proc. SPIE 3802, Advanced Optical Data Storage: Materials, Systems, and Interfaces to Computers, (22 November 1999);

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