Selenium-loaded zeolite (ZSM-5): I. Structures and fundamental properties

Abstract

Atomic structures of Se clusters impregnated into ZSM-5 single crystals have been investigated through structural and optical experiments. Raman-scattering spectroscopy suggests that Se in the zeolite takes single chain structures. X-ray diffraction implies that the chains form fourfold ͑not threefold as in trigonal Se͒ helices. The chain length is estimated from weight and electron-spin resonance measurements at 10 2 atoms. The material shows an optical absorption edge at ប Ӎ 2.2 eV, which accompanies dichroism, suggesting chain alignment in the zeolite pores.

Optical nonlinearities of Se-loaded zeolite (ZSM-5): A molded nanowire system

“…It is plausible that this gradual slope arises from structural inhomogeneity, i.e., Se is impregnated as a form of single chains with an average chain length of 10 2 atoms, which possibly varies from site to site. 13 Then, defining the optical gap as a photon energy at the absorption coefficient ␣ of 10 3 cm −1 , we have E g Ӎ 2.2 eV, which blueshifts by ϳ0.2 eV from the bulk gap. Figure 3͑a͒ also compares ␤ spectra of g-Se and z-Se, which have been evaluated from intensity-dependent transmittances of light pulses emitted from the OPO.…”

“…On the other hand, z-Se is opaque at Շ600 nm. 13 Figure 2 shows a result of the imaging z-scan measurement for a z-Se sample at Ӎ 1064 nm, pulse width of 5 ns, and irradiance of ϳ0.5 GW/ cm 2 . We see for the central intensity ͑open circles͒, which corresponds to the closedaperture signal, a valley-peak distance of ϳ140 m, and a normalized valley-peak transmittance of ⌬T p-v Ӎ 0.3, which gives n 2 Ӎ 10 −3 cm 2 / GW with sample-to-sample variations of a half order.…”

“…Fundamental properties of Se-loaded ZSM-5 have been reported elsewhere. 13 Two kinds of samples were investigated. One was z-Se, the preparation detail being reported in Ref.…”

“…One was z-Se, the preparation detail being reported in Ref. 13. In short, ZSM-5 crystals with a typical dimension of 40ϫ 40 ϫ 200 m 3 for the a, b, and c axes ͑see Fig.…”

“…14 Optical transmission spectra of these samples were evaluated using a laser-detector system. 13 Two-photon absorption coefficient ␤ and intensity-dependent refractive index n 2 were measured using three pulsed sources: a 5 ns yttrium aluminum garnet ͑YAG͒ laser, an optical parametric oscillator ͑OPO͒, and a 0.3 ns YAG laser. Optical setups employed were two kinds.…”