Second Harmonic Generation of C60Incorporated in Alkali Metal Ion Zeolites and Mesoporous MCM-41 Silica

Different loadings of C60 have been incorporated in mesoporous MCM-41 aluminosilicate as well as proton and alkali metal ion zeolites. These samples show non-linear optics activity whose efficiency increases upon C60 content, size of the alkali metal ion, and laser exposure. The later unprecedented second harmonic generation (SHG) enhancement effect can lead up to 2 orders of magnitude efficiency increase. After having irradiated the solid, the SHG enhancement decays upon standing in the dark toward the initial value of fresh and unexposed samples. EPR measurements and alternative generation of zeolite electron−holes ions pairs have ruled out triplet excited states and radical ions as responsible for this enhancement upon irradiation. One proposal at the moment is that this SHG activity enhancement arises from unstable photoproducts such as photoadduct or dimers. However, attempts to isolate any C60-derived photoproduct have met with failure so far.