The xanthenium cation has been spontaneously generated by adsorption of 9-xanthenol within several acidic (HY, HMor, and HZSM5) zeolites. The resulting composites were characterized by diffuse reflectance and luminescence spectroscopy and were found to be stable over an extremely long period of time. Time-resolved diffuse reflectance of these samples at several excitation wavelengths allowed the identification of a 540-nm band to the triplet state of the cation in the zeolite environment. The triplet state in the zeolite was found to have a much longer lifetime than related triplet xanthenium cations insolution. The observation of the 9-xanthylium radical requires the participation of an electron donor; the question is raised as to whether the zeolite framework can play this role.