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Resonance Raman scattering of the radial breathing mode in single wall carbon nanotubes AIP Conf.The first-and second-order Raman phonon spectra of CsPbCl 3 were measured in phase IV using Raman and resonance-Raman scattering. Twelve Raman active phonons were resolved at 32, 35.5, 42, 52, 72, 90, 110, 115, 121, 189, 200.5, and 375 cm Ϫ1 and correlated to the phonon spectrum of CsPbCl 3 in phase I. The highest frequency longitudinal optical mode is 375 cm Ϫ1 .

Surface-enhanced Raman scattering (SERS) has proved to be an effective technique for studying the structural properties of conducting polymer thin films. The enhancement process has a twofold origin, electromagnetic and chemical. The electromagnetic enhancement, which is the dominant mechanism in SERS generation, consists in the excitation of localized and delocalized surface plasmons (SPs) in the metallic support of the thin film. The Raman emission of the adsorbed molecules on the metal surface (the most efficient being Ag, Au and Cu) is due to the intense evanescent electromagnetic field located at the interface between the metal and the surrounding medium. The second enhancing mechanism for SERS is of chemical origin, involving the formation of new chemical bonds between the molecules and the metal surface, with the polarizability thus becoming considerably higher than that of the free molecules. This mechanism is as a rule accompanied by a metal-molecule or molecule-metal charge transfer, which partly accounts for the success of the SERS studies on conducting polymers. Unfortunately, these studies have revealed that the chemical effects at the polymer-metal interface varied substantially depending on the various types of polymer and metallic support. In this context, polyaniline containing two different entities (a reduced and an oxidized state) in its repeating units exhibits specific alterations in its SERS spectra depending on the type of metallic support. This paper presents new results concerning the structure of emeraldine-base and emeraldine-salt polyaniline thin films deposited on rough Ag and Au supports. The effect on the SERS spectra of the polymer-metal and polymer-ambient interface chemical reactions is also described. The presence of an interface compound depending on the oxidizing properties of the metallic support has a strong influence on the SERS spectra, no matter how the PAN films were deposited on the support (whether by solvent evaporation or by an electrochemical process, i.e. cyclic voltammetry). When an emeraldine base is doped with HSO 4 − ions, it turns into an emeraldine salt, which exhibits a disordered state in its macromolecular chain, leading to a modified profile of the ∼1162 cm −1 Raman line which is associated with the C-H bond of the quinoid ring. The Lorentzian profile is altered by the addition of a Gaussian profile component. For a rough Ag support, the SERS spectra show that the transformation of emeraldine base films into emeraldine salt films is a reversible process.

Through correlated studies using scanning electron microscopy (SEM), Raman spectroscopy and low-temperature photoluminescence (PL) we have demonstrated that the intercalated PbI2 with ammonia, poly (vinyl alcohol) and polyacrylamide are characterized by a distinctive signature in the Raman and photoluminescence spectra. After intercalation, the Raman spectrum of PbI2 reveals an orthorhombic structure, identical with that observed on the micrometric scale, of KPbI3 rod-like particles resulting from the reaction between Pb(NO3)2 and KI, carried out in liquid media such as ethanol and acetonitrile. The rods and the intercalated PbI2 are characterized by a new and strong emission band at 2.23 eV (about 550 nm) that appears at 77 K under an excitation wavelength of about 340 nm. Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the PbI2 layers of different molecular species. The compression acting primarily on the iodine layers has the result of lowering the contribution of the 5p states of I− ions to the constitution of the electronic level situated at the top of valence band of PbI2, so that the photoluminescence of intercalated PbI2 acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.

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Scanning electron microscopy, Raman scattering, UV-VIS absorption spectroscopy and low temperature photoluminescence (PL) were used to examine small particles produced by the chemical reaction between Pb(NO 3 ) 2 and KI in different liquid media: water, methanol, ethanol and acetonitrile. By stoichiometric changes in the synthesis reaction, platelets of PbI 2 and rods probably of KPbI 3 are produced. Regardless of shape and size, these particles exhibit almost the same PL, which consists of two intense bands centred around the 2.5 (E band) and 2.0 eV (G band), in turn similar to that of a crystalline slide or a micrometric powder, both prepared from a PbI 2 single-crystal grown from the melt. Crystalline PbI 2 platelets exhibit an E band with two components, at 2.49 (E F band) and 2.47 eV (E T band), originating in the recombination of the free and trapped excitons produced by inter-band irradiation. A close relation between the enhancement of the E T and G band reveals that they are linked to the surface defects. For the rod-like particles, the PL spectrum is somewhat similar to that of a Pb 2+ ion introduced into an alkaline halide lattice, which as for any ns 2 ion displays two emission bands, A T and A X , whose correspondents are E and G bands.

Optical absorption, photoluminescence, and Raman scattering spectra of poly(para-phenylene vinylene) (PPV) and single-walled carbon nanotube (SWNT) composite films are investigated at room temperature. Samples have been prepared at different precursor conversion temperatures, T c , (300, 180,and 120°C) and with SWNT mass concentrations from x) 0% up to 64%. In each sample, we observe drastic changes in all optical absorption spectra of PPV and composite films. In particular, after conversion at T c) 120°C, PPV samples exhibit photoluminescence (PL) with a new feature at about 2.55 eV together with less-intense ones at about 2.37 and 2.20 eV, respectively. The most-intense at 2.55 eV is due to a radiative recombination on the shorter conjugated segments and interpreted from a theoretical model based on a distribution of conjugated lengths. This distribution, which allows an assignment of all PL peaks, is also able to explain all experimental data including Raman scattering and optical absorption spectra in a given sample. Also, further changes in PL and optical absorption spectra are observed by increasing the SWNT concentration in composite films converted at the same temperature. We have also investigated the effect of the dilution of the precursor polymer solution. From the theoretical analysis of the optical absorption, PL, and resonance Raman spectra, we show that PPV samples are characterized by a decrease of the effective conjugation lengths when the precursor dilution increases. All experimental data are explained well with a bimodal distribution model reflecting an effective inhomogeneity in the polymer as suggested already from morphological pictures issued in particular from X-ray data.