EXPERIMENTAL INVESTIGATIONS OF TEMPERATURE AND HOST EFFECTS ON PHOSPHORESCENT TRIPLET STATE IN MIXED ORGANIC CRYSTALS

Detailed experimental studies on the temperature and host effects of phosphorescent guest molecules in mixed organic crystals are reported. Temperature-dependent triplet-state energy transfer from guest to host and guest to guest in the systems with small guest-host triplet-state energy separation was studied in a benzophenone host using phenanthrene-Ao, naphthalene-ds, and 2-methylnaphtb.alene as guest. Rate constants and activation energies were estimated for this type of transfer. Detailed studies on the temperature dependence of the lifetimes of guest triplet states in various substituted benzene hosts were made. The possible causes of the temperature dependence of lifetimes in such systems are discussed in detail. Preliminary results of the host effect on the zero-field parameters and lifetime of naphthalene-ds in some chloro-substituted benzene hosts are also reported.