Nature and Dynamics of Photoexcited States in KTaO_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We have investigated luminescence spectra and their decay kinetics in potassium tantalate (KTaO_3) to reveal the nature and dynamics of the photoexcited states. The temperature dependence of the absorption spectra indicates electron-phonon coupling in KTaO_3 that is sufficiently strong to stabilize self-trapped excitons. We attribute the observed 2.5 eV luminescence to the self-trapped exciton luminescence. The decay kinetics of the 2.5 eV luminescence is found to be nonexponential with power-law behavior and shows a long lifetime of several milliseconds at 5K, which indicates separate localization of photoexcited electrons and holes. Similar decay profiles are also observed in the oxygen-deficient and lithium-doped crystals. The decay kinetics is successfully reproduced by a model based on the tunneling recombination process. The model calculation of the excitation density dependence reveals that the number of localized electrons should be finite, which gives rise to the conductive electrons overflowing from the localized states. These results support the Maxwell-Wagner model for the photoinduced giant permittivity in KTaO_3.
社団法人日本物理学会の論文
2006-06-15