111 research outputs found
Photoconductivity and the structural phase transiting in SrTiO3
No full textDetailed photoconductivity measurements have been performed in nominally pure SrTiO3 in order to elucidate the effect of the antiferrodistorsive cubic-tetragonal phase transition.
Small features in the photoconductivity's temperature dependence in the phase transition region were found using low intensity interband UV or 514 nm light illumination.
Such features are associated with a transformation of the defect system controlling the photoconductivity.
At the same time, the temperature behavior of the photoconductivity spectral maximum reveals a rather unusual
feature which is connected with changes in the absorption band edge structure in the phase transition region. (c) 2006 Elsevier Ltd. All rights reserved
New occurrence of fire opal from Bemia, Madagascar
No full textTwenty-two gem opals from a new volcanic deposit located near Bemia, in southeastern Madagascar, were investigated by classical gemological methods, SEM-EDS, powder X-ray diffraction analysis, LA-ICP-MS, and Raman and IR spectroscopy. Although none of the opals show play-of-color, they exhibit a wide variety of hues-- including those typical of fire opal--that are related to iron content, mainly from Fe-rich inclusions. Consistent with their volcanic origin, these samples are microcrystalline and composed of opal-CT or opal-C. Among the inclusions were ilmenite needles, clay minerals, and iron oxides and hydroxides. The RI and, in particular, SG values were higher than those typical of natural fire opal (e.g., from Mexico) and some synthetic fire opal, allowing for a rapid separation
Impurity effects and charge transport in ABO3 single crystal oxides: Photorefractivity-oriented and basic studies
No full textNon linear optical, dielectric, magnetic properties of ABO3 single crystal oxides let the implementation of acousto-optic, electro-optic, photonic, spintronic devices. In particular, significant role is played by the ferroelectric and photorefractive materials, where the photo-induced change in refractive indexes requires charge transport and impurities which support charge transfer, space charge formation and localization with accompanying electric field. Besides, ABO3 paraelectric perovskites regularly reveal newel effects connected with charge transport, e.g., photo-induced polar state recently reported for SrTiO3 and KTaO3. In this work we review our recent investigation, pointing out our studies of photo-transport in SrTiO3, Cu-doped KTaO3 and LiNbO3:Hf
Role of the Zhang-Rice-like exciton in optical absorption spectra of CuGeO3 and CuGe1-xSixO3 single crystals
No full text
Optical and Structural Property Tuning in Physical Vapor Deposited Bismuth Halides Cs3Bi2(I1- xBrx)9(0 ≤ x ≤ 1)
No full textCrystalline films of lead-free all-inorganic Cs3Bi2X9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs3Bi2I9 to 2.64 eV for Cs3Bi2Br9. X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts
Characterization study of coal spontaneous combustion by EPR spectroscopy
No full textIn the present paper the low temperature treatment (up to 200 °C) of
the coal was examined by the EPR, using 6,2 and 1,86 mW microwave radiation. During
the heat treatment the formation of intermediate radicals has been revealed.Belarusian Republican Foundation for Fundamental Research.This work was supported by the CICOPS-2016 fellowship program, University of Pavia, Italy and the project #P2016–1216 from the Asian Research Center in Mongolia
Characterization of waveguides obtained by proton exchange on a LiNbO3 substrate
No full textWaveguides obtained by proton exchange in LiNbO3 were characterized by Secondary Ion Mass Spectrometry and m-lines technique. Additional micro-Raman investigations evidenced marked changes in the spectra of the waveguide with respect to the substrate. This suggests that micro-Raman spectroscopy may constitute a direct non-destructive method to determine the depth of the exchanged layer, with a limit which is set by the diffraction-limited spot size
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