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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

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Relative quantum yields and decay kinetics of exciton phosphorescence (0-0 band a t 412.46 nm) and those of XI-traps (0-0 band at 413.54 nm) are measured versus t,he exciting light intensity in 4,4'-dichlorobenzophenone single crystals a t 1.5 and 4.2 K. The phenomena observed are treated from the point of view of mutual annihilation of triplet excitons, whose rate constant, equal to (4.2 5 2.0) i em3 s-l, is unchangeable in the temperature range studied. Equivalent free excitons are shown to be responsible for mutual annihilation. The decay kinetics of X,-trap phosphorescence is explained by optical spin alignment in the excited triplet state. npll 1 , s H 4,2 B MOHOKpLlCTaJIJIaX ~,.2'-nHXnOp6eH30$leHOHa l23iMepeHbI OTHOCLITeJIb-HLIe KBaHTOBbIe BblXOHbI H I-FHHeTHIia 39TYXaHLIR $lOC@OpeCUeHUllH 3KCEITOHOB (0-0 no-MHTeHCEIBHOCTLi BO36ym~aIoWerO CBeTa. Ha6n1o~ae~b1e RBJIeHLlR HHTepIIpeTHpOBaHbI C T 0 9 K k I 3peHHH B3aGTMHOfi aHHH~HJWUHH TPHIIJIeTHblX BKCMTOHOB, KOHCTaHTa CKOPOCTLl KOTO-POI% paBHa ( 4 , 3 & 2,o) :". Cm3 S-l 12 Heli3MeHHa B yKa3aHHOM TeMIIepaTypHOM €311-TepBane. nOKa3aH0, YTO 3 9 B3aHMHYH) aHHIIIX2JIRUHIo OTBeTCTBeHHLI CBO60nHb1e BKBHB9-;IeHTHLIe 3KCLITOHbI. K' EIHeTHIEa 3aTyXaHHFi ~OC$lOpeCI~eHUHEI X1-JIOByIIIeK 06.6HCIIeHa OIITEI9eCHOfi C l l L l H O B O t OpHeHTaUkIefi B HX BO36ymAeHHbIX TpHnJIeTHbIX COCTORHURX. zoca npu 412,46 nm) EI Xl-noBymeH (0-0 nonoca npa 413,54 nm) B ~~B E I C E I M O C T H OT [20] V.