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Thin films and crystalline powder of PbI2 intercalated with ammonia or pyridine have been studied by optical absorption, Raman scattering, photoluminescence, FTIR spectroscopy and thermo-gravimetric analysis. Ammonia intercalated PbI2 shows an increased optical band gap, of about 0.6 eV, with an intense broad emission band peaking at about 2.3 eV as signature in the photoluminescence spectrum. The intercalation of PbI2 with ammonia is noticed in the Raman spectrum by the appearance of new lines situated in low frequency range. The D3d coordination geometry of Pb2+ in the PbI2 crystal is reduced by compression to orthorhombic one, the distribution of the electronic states in valence band is also changed. Thus, the top of the valence band undergo a deformation inducing a weakness of the interaction between the lead and iodine ions within a layer. Also the PbI2 intercalated with pyridine is featured by optical and vibration properties different that of pure crystalline powder. Finally, the intercalation of PbI2 with different molecules changes the basic semiconducting properties of the crystal. Thermal analyses and infrared absorption spectra have been used to study the desorption of guests species from PbI2 in order to evaluate the stability range and morphological changes with temperature. [ABSTRACT FROM AUTHOR]

The paper describes a simple low-temperature synthesis route of preparing bismuth ferrite thin films through a wet chemical process, using nitrates of bismuth and iron and two chelating agents (citric acid and polyvinyl alcohol). The films were successively deposited on different type of substrates (silica glass, steel and sintered alumina) using the immersion technique. After specific annealing, in air, the samples were characterized by scanning electron microscopy (SEM), spectroellipsometry (SE), X-ray diffraction (XRD), X-ray photoelectron (XPS) and Raman spectroscopy. The influence of chelate agent and the nature of substrates on the mechanism formation of BiFeO3 is emphasized. [ABSTRACT FROM AUTHOR]