首页|Raman and optical absorption spectra of oriented Se8 and Se_(12)rings formed in zeolites: Dependence on the Se loading density
Raman and optical absorption spectra of oriented Se8 and Se_(12)rings formed in zeolites: Dependence on the Se loading density
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We encapsulated selenium(Se)into AFI and LTA zeolites via Se vapour adsorption at-450 ℃ and studied Raman and optical absorption spectra(RS and OAS,respectively)of zeolite single crystals with incorporated Se.At high Se loading density(D),Se8 rings are formed in the AFI channels along with Se chains.The rings are oriented by their 4-fold axis parallel to channels.Se8 is also formed in the LTA large cavities with its 4-fold axis oriented parallel to the 4-fold axis of LTA at any D up to ~8 Se atoms per cavity(at/c).However,at D > 0.5 at/c,nearly unexplored Se_(12)rings oriented by their 3-fold axis parallel to the LTA 3-fold axis are formed along with Se8 in neighboring cavities.We discriminate between Se8 and Se_(12)rings via 1)RS frequencies; 2)RS and OAS band intensities vs.D; 3)RS band intensities vs.excitation wavelength and light polarization configuration.With an increase in D,the number of Se_(12)rings grows faster than that of Se8.We extract OAS of Se8 and Se_(12)from the experimental AFI-Se and LTA-Se OAS and show that the 3.0-3.3 eV absorption of Se_(12)is enhanced compared to that of Se8.This absorption is responsible for the observed resonant Raman effect of Se_(12)at the 514.5 nm wavelength excitation.Both LTA-confmed Se8 and Se_(12)display rather high thermal stability.
Zeolite single crystalsSelenium clustersRaman microscopyOptical absorption spectroscopy
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