Photochemical Behaviour of Luminescent Dyes in Sol-Gel and Boric Acid Glasses
Fluorescence of organic colorants is generally enhanced by high viscosity of the surrounding medium, having much fewer energetic collisions with the excited state, and perhaps also preventing large distortions along unsymmetrical vibrational modes. However, this is not simply determined by the macroscopic viscosity (Lewis and Calvin 1939) since cool glycerol is much more effective than a lubricating oil at the same low temperature. We are here studying fluorescein, belonging to the category of xanthene dyes (the heterocyclic xanthene is two benzene rings connected with two bridges in ortho-position, one being an oxygen atom and the other CH2) like the various substituted eosine and rhodamine modifications. In many cases, their quantum yield η is above 0.9, and corresponding to their very strong absorption bands in the visible, the life-time τ of fluorescein is only 4 nanoseconds in water and alcohols (Martin 1975).
KeywordsTriplet State Excited Singlet State Delayed Fluorescence Photochemical Behaviour Beta Process
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