Optical properties of ultrafine carbon nanotubes in ZSM-5 zeolites

By using ZSM-5 zeolites as a template, we fabricated ultrafine carbon nanotubes with a diameter of 3–4 Å in the channels of ZSM-5 (SWNTs@ZSM-5). These novel carbon materials show fancy properties due to their small dimensions. Raman spectroscopy of SWNTs@ZSM-5 was carried out using a variety of excitation energies, and three types of single-walled carbon nanotubes with chiral indices of (4,2), (3,2), and (3,0) were identified. Among them, the diameter of the (3,0) nanotube is only 3 Å, which is one of the smallest carbon nanotubes. The (4,2) and (3,2) nanotubes are semiconducting, while the (3,0) nanotube is metallic. In addition, the photoluminescence (PL) spectra of SWNTs@ZSM-5 were characterized. There is only one peak on the fluorescence spectrum with an excitation energy of 3.780 eV and an emission energy of 3.171 eV, which match very well with the (4,2) nanotube’s fourth optical transition energy of 3.787 eV and the third optical transition energy of 3.174 eV calculated from the density functional theory simulation.