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Raman spectra of single-wall carbon nanotubes produced in the channels of zeolite AFl single crystals have been analyzed in the light of the full symmetry group, the line group. The phonon dispersion curves of the tubes (5,0), (3,3), and (4,2) are calculated based on the lattice dynamical model and the phonon branches are assigned to their quantum numbers (irreducible representations). The structures of Raman spectra of different samples are reproduced well by the density of states of relevant Raman-active phonons. The result is useful to evaluate the contents of these tubes in real crystals where the contents are not well defined before. [ABSTRACT FROM AUTHOR]

Detailed synthesis process of selenium species incorporated in the channels of AlPO4-5 zeolite single crystals is reported. X-ray scattering experiments show diffuse planes which can be analyzed in terms of a partial filling of the channels by helical selenium chains. Polarized Raman and polarized absorption spectra confirm that the helical chains are highly aligned along the channel direction, while the rings appear randomly distributed in the channels. The helical chains have a lowest optical absorption band at 2.6 eV that is strongly polarization dependent, while the rings have a lowest absorption band at 3.0 eV that varies slowly with the light polarization. [Copyright &y& Elsevier]

Abstract: Decomposition mechanism of dipropylamine (DPA) molecules in the channels of AlPO4-11 and Si-incorporated AlPO4-11 (SAPO-11) zeolite crystals was investigated by mass spectrometry, with the aim to fabricate high-density 0.3-nm single-walled carbon nanotubes (SWNTs). In comparison with neutral AlPO4-11, the organic template DPA is bonded to SAPO-11 framework by strong chemical interaction. As a result, a significant amount of hydrocarbon molecules are trapped in the channels during carbonization process. In addition, the SAPO-11 framework plays an important catalytic role in the pyrolysis and conversion of the organic molecules to SWNTs within the crystal channels, owing to the Bønsted acid sites. The resulting SWNTs have higher density than those fabricated without Si doping, evidenced by the clear and strong radial-breathing modes in Raman spectra. [Copyright &y& Elsevier]

Emission spectroscopy is performed to study the optical transitions between electronic bands of SWCNs formed in AlPO4−5 (AFI) crystal. Strong visible emission is observed under laser light illumination at room temperature. The emission is excited by the light polarized along the c-axis and its polarization is also along this direction. On the other hand, non-linear emission is observed under the resonant excitation of the lowest absorption band of SWCNs. The emission is excited by the light polarized along the c-axis, but it shows the polarization perpendicular to the c-axis. The polarization character is discussed on the basis of the selection rules of the optical transitions predicted by the full line-group symmetry of SWCNs. [Copyright &y& Elsevier]

Photo-induced electric current modulation is studied in AFI-SWCNs systems by visible and near infra-red laser light at room temperature. Remarkable polarization anisotropy in the modulation is observed. λ-dependence of the polarization anisotropy is analyzed by a simple model based on the optical anisotropy observed in absorption spectra. [Copyright &y& Elsevier]