Intrazeolite photochemistry.: 26.: Photophysical properties of nanosized TiO2 clusters included in zeolites Y, β, and mordenite

The photophysical properties of TiO2 included in zeolites Y, beta, and mordenite are determined using time-resolved techniques. The shift in the ground-state absorption spectra for the TiO2-zeolite samples, compared to bulk phase anatase, is attributed to a direct transition in the semiconductor, based on calculated electronic transition energies. Excitation of the samples at 355 nm results in the formation of a trapped electron. Time-resolved fluorescence spectra are dependent upon the sample treatment, that is, whether the sample is heated prior to monitoring of the emission. Significant changes were found in the emission lambda (max) and decay kinetics. These changes that occur are due to the presence of two different Ti species in the nanoclusters, differing in the presence of hydroxyl groups bonded to Ti atoms, that in turn depends on the thermal treatment and the relocation/redistribution of water around the Ti atoms. Changes in relative intensities between the two sets of samples are attributed to defect sites that are produced upon heating of the sample at high temperatures.