Features of the near-infrared phosphorescence of singlet oxygen 1 O 2 photosensitized by TiO 2 in solutions have been investigated. The short-lived phosphorescence of 1 O 2 with spectral maximum at approximately 1300 nm is observed to follow excitation by pulsed laser radiation at 355 nm of TiO 2 suspended in CCl 4 and water H 2 O. The shorter lifetime and spectral shift of this phosphorescence, as compared with phosphorescence of 1 O 2 sensitized by phenalenone in these solvents, are attributed to the adsorbed state of emitting singlet oxygen. The observed laser pulse energy dependence indicates the two-photon and three-photon nature of this phosphorescence initiation in CCl 4 and H 2 O, respectively. The formation of 1 O 2 in CCl 4 is assumed to be provided by the sequence of one-photon excitation of TiO 2 , giving rise to superoxide anion O 2 − and one-photon photodetachment of electron from O 2 − . The photodetachment of electron from O 2 − in water H 2 O is a two-photon process because of higher solvation energy of superoxide anion in water. The processes that govern the rise and decay of singlet oxygen phosphorescence sensitized by TiO 2 are discussed. The factors affecting the yield of singlet oxygen provided by electron photodetachment are also considered.
A collision-induced photon echo arising at the transition 0 ↔ 1 of ytterbium in the presence of heavy atomic buffer is investigated. Collision-induced echo signal appears in the case of mutually orthogonal linear polarizations of exciting pulses and it is absent without buffer. Collision-induced echo power grows with buffer pressure up to the maximum value and decays exponentially at further buffer pressure growth. Collision-induced echo power is essentially less than that of the ordinary echo generated by pulses with parallel polarizations in the same mixture, and its polarization is linear with the polarization vector directed along that of the first exciting pulse. All the properties of collision-induced photon echo are explained on the basis of collision relaxation dependence on the direction of active atom velocity.
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