Xerogels excitation spectra

As was earlier reported, flexible properties of sol-gel technology may be used for modification of PLE spectra of the incorporated lanthanides. In particular, appearance of the strong band at PLE spectrum at 360 nm for the emission wavelength 1.54 pm was observed for the erbium-doped monolith xerogel silica-titania or titania/opal structure [3,4], However, in ftie case of excitation terbium in composite YAG/titania xerogel/opal the obtained PLE... 

For the samples comprising of PAA coated with Eu-doped xerogel typical PL spectrum measured at the excitation wavelength of 368 nm is presented in Fig. 2. It reveals the presence of clearly pronounced PL band at 475 nm visible to the naked eye which corresponds to inherent blue photoluminescence of PAA. Well-resolved optical band at 613 nm corresponding to Do-> F2 electron transition of Eu ions in the fabricated structure is also observed from the spectrum but red emission can not be seen with the naked eye. 

PLE spectrum measured for 1.54 pm emission line in xerogel embedded in PAA (Fig. 4, curve a) reveals a set of the well-resolved excitation bands with the most intense band at 524 nm coinciding with the direct excitation of erbium through the 4Ii5/2 — 2Hn/2 transitions. 

The fluorescence spectrum of pyrene has been very often nsed as a photophysical probe. The fluorescence spectmm shows the vibronic strnctnre, which is sensitive to the polarity of the environment (Nakajima, 1971 Kalyanasnndaram, 1977). Moreover, pyrene forms excimer due to one molecnle in the groimd state and one in the excited state for concentrated systems. Therefore, fluorescence spectra of pyrene can be expected to reveal the stmctnral changes of sol-gel silica and trapping mechanism of organic molecnles along the sol-gel-xerogel transitions... 

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