Light-induced absorption changes in ferroelectric crystals:SrxBa1-xNb2O6:Ce; KTaO3; KTa1-xNbxO3

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Title: Light-induced absorption changes in ferroelectric crystals:SrxBa1-xNb2O6:Ce; KTaO3; KTa1-xNbxO3
Authors: Gubaev, Airat
Thesis referee: Prof. Dr. M. Reichling
Junior-Prof. Dr. M. Imlau
Dr. Pankrath
Abstract: The aim of the current work was to investigate the photo-induced charge transport at low temperatures, allowing more sensitive, detailed measurements of the first steps in the build-up of space charge fields, which modify the refractive index, leading to modern applications like volume holographic storage. We investigated the light-induced properties of SBN:Ce, KTO and KTN materials like origin of trapping centers which are involved in the charge transport process, characterization of trapping centers, like temperature dependence, illumination intensity dependence, evolution with time, spectral response, activation energies, the basic properties of the electronic excitations and photo-carriers localization based on results of absorption, light-induced absorption, photoluminescence, and photocurrent. The main contributions of this dissertation are summarized as follows: The experimental intensity dependence, temperature dependence, and decay process of the light-induced polaron (NIR) and VIS center absorption can be fitted with the help of a simplified charge transfer model (for SBN). The decay observed of the NIR polaron and the VIS centers is present due to the Fourier spectrometer light. The dissociation of the VIS centers into NIR centers under red light was observed. The model proposed for the VIS-centers in SBN is a triad structure related to the simultaneous bonding of two hole polarons and one electronic polaron.In KTN the emergence of the UV-light induced wide absorption bands in the NIR region with maxima at 0.69 0.8 eV at low temperatures is treated as a manifestation of the localization of photo-induced electrons and the formation of small electron polarons in close-neighbor Nb-Nb pair centers. Also, these properties in KTN can be fitted with the help of the simplified charge transfer model.
Subject Keywords: SBN; Ce; KTO; KTN; polaron; charge transfer vibronic exciton; photo-induced; charge transport
Issue Date: 20-Dec-2005
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB04 - E-Dissertationen

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