Specific features of the exciton+xciton annihilation process for slow diffusion systems are considered in terms of excimer luminescence in pyrene crystals. I n this case luminescence decay curves allow a direct determination of the diffusion coefficient and the mean free path of the excitation during its lifetime. Analogy between excimer excitations and the well-known slow excitons is discussed. The importance of the experimental separation of excinier and monomer excitons whose kinetic parameters are greatly different is emphasized.Die spezifischen Charakteristika des Exziton-Exziton-Vernichtungsprozesses fiir Systeme mit langsamer Diffusion werden anhand der Exzimer-Lumineszenz in Pyrenkristallen betrachtet. In diesem Fall erlauben die Lumineszenzabklingkurven eine direkte Bestimmuiig des Diffusionskoeffizienten und der mittleren freien Weglange der Anregung wilhrend ihrer Lebensdauer. Die Analogie zwischen Exzimer-Anregungen und den wohlbekannten langsamen Exzitonen wird diskutiert. Die Wichtigkeit der experimentellen Trennung von exzimeren und monomeren Exzitonen, deren kinetische Parameter sehr verschieden sind, wird betont.

Intercalation of C 60 single crystals with helium was studied by powder x-ray diffractometry. It was established that the intercalation is a two-stage process, octahedral cavities are filled first and then tetrahedral ones, the chemical pressure being negative during both stages. For the first time low-temperature (5 K) photoluminescence spectra of helium-intercalated fullerite C 60 were studied. The presence of helium in lattice voids was shown to reduce that part of the luminescent intensity which is due to the emission of covalently bound pairs of C 60 molecules, the so-called «deep traps» with the 0-0 transition energy close to 1.69 eV. The mechanism of the effect of the intercalation with helium on the pair formation in fullerite C 60 is discussed.

For the first time peculiarities of the formation of Dicke optical superradiance are studied experimentally and theoretically in a pyrene-doped biphenyl crystal under active phonon effect (the energy level is lAgJBzu; wavelength 373.93 nm; pyrene concentration 0.25 molyo; temperature 1.5 to 4.2 K). The possibilities of this phenomenon to obtain spectroscopic data are demonstrated. The pseudolocalized phonon lifetime tphon and the activation energy AE are estimated to AE = (7 3) cm-' and tphon = 2 to 20 ps by the temperature dependence of the superradiance intensity. Erstmalig wurden Besonderheiten der Bildung des optischen

We present the results of investigation of low-temperature (5 K) photoluminescence of thin fullerite C60 films of various structures obtained on monocrystalline NaCl substrates by vacuum deposition at temperatures in the interval 290–400 K. Depending on the conditions of deposition, the film structure, which was controlled by the standard transmission high-energy electron diffraction (THEED) technique, varies from a disoriented structure to an oriented structure with different average sizes of microcrystals. The effect of the film structure on the photoluminescence spectral band of fullerite, associated with the luminescence of structural defects (X-traps), is attributed to the peculiarities of transport and capture of coherent singlet excitons in single crystals of various sizes.