Influence of chemical reduction on the particular number densities of light-induced small electron and hole polarons in nominally pure LiNbO3

Autor(en): Merschjann, C.
Schoke, B.
Imlau, M. 
Stichwörter: CENTERS; DEFECTS; INDUCED INFRARED-ABSORPTION; LIB3O5; LITHIUM TRIBORATE; Materials Science; Materials Science, Multidisciplinary; MOTION; PARAMAGNETIC-RESONANCE; Physics; Physics, Applied; Physics, Condensed Matter; TIME
Erscheinungsdatum: 2007
Volumen: 76
Ausgabe: 8
The influence of chemical reduction on the particular number densities of light-induced free small Nb-Nb(4+) electron polarons, bound small Nb-Li(4+) electron polarons, bound small Nb-Li(4+):Nb-Nb(4+) electron bipolarons, and bound small O- hole polarons is investigated in nominally pure, congruently melting LiNbO3 by means of excited-state absorption spectroscopy. Characteristic changes in the sign of the light-induced absorption in the blue-green spectral range and distinctive dependencies on the pump beam intensity reflect the increasing contribution of electron polarons generated upon single intense ns-laser pulses at lambda=532 nm with increasing degree of reduction. The entire data set including its time dependence and spectral properties is consistently explained within a model taking into account the presence of all four types of electron and hole polarons, and residual Fe2+/3+ impurities. The model includes one- and two-photon excitation processes for polaron generation, optical gating of bipolarons, and direct and two-step polaronic recombination processes. Our results indicate a mutual independence of two-photon hole polaron generation and one-photon dissociation processes of bipolarons, at least for moderate degrees of reduction.
ISSN: 24699950
DOI: 10.1103/PhysRevB.76.085114

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