Nanocrystalline SrTiO3:Eu3+ and BaTiO3:Eu3+: fluorescence spectroscopy and optical studies of structural phase transitions

The results of optical studies of Eu3+ ions doped nanocrystalline materials which undergo structural phase transitions: SrTiO3:Eu3+ and BaTiO3:Eu3+ are presented. Nanocrystalline SrTiO3 and BaTiO3 samples with crystallite sizes about 25-50 nm were produced by the sol-gel process. The Eu3+5D0,1 → 7Fn fluorescence spectra were studied. Time-resolved fluorescence spectra enabled to separate different kinds of Eu 3+ centers in BaTiO3 samples. Fluorescence spectroscopy of probe Eu3+ ions was used to detect the structural Oh-D4h phase transition in nanocrystalline SrTiO 3. The Eu3+ excited states lifetimes were studied in a wide temperature range and the effects of modified refractive index of the media on radiative transitions were observed. The study of ferroelectric C4v-Oh phase transition in nanocrystalline BaTiO3 with optical second harmonic generation technique revealed remarkable hysteresis in the temperature dependence of the second harmonic intensity. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)