Optical properties of guest-host nanocomposite materials

Aluminophosphate AIPO(4)-5 single crystal is a kind of nanoporous material. Its framework consists of alternative tetrahedra of AlO4 and PO4 which form an array of opened one-dimensional channels and pack in hexagonal structure as two-dimensional photonic crystal. The inner diameter of the channel is 0.73 nm. Since the AlPO4-5 single crystal is electrically insulated and thermally stable up to 900 degrees C, it is an ideal host to incorporate nano-structured species. These guest-host materials are potentially new functional materials in electric transport, optic switches, nonlinear optics and lasers. We have synthesized two different types of guest-host systems, including selenium and carbon nanotube in the channels of AlPO4-5 crystals. Polarized absorption spectra and polarized Raman spectra have been investigated. Both crystals behave as good polarizers with high absorption for the light polarized parallel to the c-axis of the crystal. This anisotropic optical property implies that ordered species with a large aspect ratio are formed in the channel. The polarization angle dependence of the Raman intensity indicates that the enclosed species are highly oriented in the channels with their dipole transition moment mostly along the channels. These guest-host systems are useful for applications of optical filters or polarizers.