Luminicence and optical second harmonic generation by dipolar microregions in KTaO3

Autor(en): Fischer, C
Horst, CAF
Voigt, P
Kapphan, S
Zhao, J
Stichwörter: defect induced microregions; FERROELECTRIC MICROREGIONS; FLUORESCENCE; incipient ferroelectric; INDUCED POLARIZATION CLUSTERS; KTaO3; LIGHT; luminescence; NOMINALLY PURE KTAO3; Nuclear Science & Technology; oxygen vacancies; PHASE; Physics; Physics, Condensed Matter; Physics, Fluids & Plasmas; RAMAN; SCATTERING; second harmonic generation; SPECTRA
Erscheinungsdatum: 1995
Volumen: 136
Ausgabe: 1-4
Startseite: 85
Seitenende: 89
The incipient ferroelectric KTaO3 being cubic down to lowest temperatures, is not expected to yield second harmonic intensity (SHG) due to the inversion symmetry of the lattice. Nevertheless a weak SHG intensity of Nd:YAG laser light is observed, which increases with decreasing temperature. This low temperature SHG is drastically enhanced in KTaO3 samples which have been reduced at 1000 degrees C in H-2-atmosphere. Simultaneously the luminescence intensity observed at low temperature (T = 80 K) with an emission at lambda(max) = 520 nm is increasing strongly upon reduction as well. This increase is not only due to a thin reduced surface layer, but rather uniform throughout the volume of the sample crystal. Oxidation at 1000 degrees C in pure O-2-atmosphere diminishes both, the low temperature SHG- and the luminescence intensity, far below the values of the pure, `as-grown' crystal. Sharp luminescence features reported to be at lambda = 687 nm in the literature and assigned to Ta3+ near oxygen vacancies, have not been observed in our crystals, neither in the as-grown, nor in the reduced or oxidized samples. The interpretation is based upon dipolar microregion around a defect core due to oxygen vacancy complexes, locally breaking the inversion symmetry.
7th Europhysical Conference on Defects in Insulating Materials (Eurodim 94), ECOLE NORMALE SUPIRIEURE LYON, LYON, FRANCE, JUL 05-08, 1994
ISSN: 10420150
DOI: 10.1080/10420159508218798

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