Photon-driven electron and atomic processes on solid-state surface in photoactivated spectroscopy and photocatalysis

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Several results of “spectro-manometric” investigations of photoinduced processes in gas–solid systems pioneered by A.N. Terenin in the Leningrad State University which gave rise to the “photonics of heterogeneous systems” continued by his disciples are discussed. The step-by-step experimental investigations of mechanisms of interrelated processes in electronic and atomic subsystems on UV–vis illuminated surface of wide-bandgap oxides are presented. A variety of complementary experimental methods such as the mass-spectrometry, the optical, luminescence and ESR spectroscopies, and the UV-photoelectron spectroscopy have been adapted to carry out in situ investigations in three phases: gas–adsorbate–surface. The primary acts of electron subsystem excitation in the sub-bandgap range are the spectral-selective and site-sensitive excitations of F- and V-type centers. The role of photoadsorption and photodesorption of oxygen as relaxation channels competing with radiative and non-radiative decay is treated. Spectral and kinetic parameters of photoexcited centers and structures of adsorbate complexes are determined. Highly active oxygen species arise at photoactivated surface, allowing oxygen vacancies to form or to heal and also to oxidize a number of adsorbed molecules. Using the time-of-flight (TOF) spectroscopy, the composition and the kinetic energy distributions of photodesorbed particles are analyzed for to obtain the dynamics of bond rearrangements and bond breaking. The results are discussed in the framework of a charge transfer approach in excited clusters. The potentialities of the presented results for probing and characterization of the electronic and atomic structure of active sites on the surface, as well as for a regulation of a number and a composition of surface defects are discussed. We have demonstrated on an example of NO x /Al 2O 3 and (NO + CO)/TiO 2 systems that proper defects of F, F + and V-type can be used for sensitization of photocatalysts to a long-wave spectral range.