DELAYED FLUORESCENCE OF MIXED CRYSTALS.

Author Institution: Department of Chemistry, Louisiana State UniversityDelayed fluorescence of a number of mixed crystals has been investigated for systems which have guest $S_{1}$ and $T_{1}$ states lower respectively than host $S_{1}$ and $T_{1}$ states, for example, phenanthrene, naphthalene and $naphthalene-d_{8}$ guests in biphenyl host, and triphenylene and $naphthalene-d_{8}$ guests in durene host. Delayed fluorescence seems to be a fairly general characteristic of these host-guest system. The experimental results can be interpreted reasonably in terms of two types of annihilation: homogenous annihilation between two similar triplets (guest-guest or host-host) and heterogeneous annihilation between a host triplet and a guest triplet. The type of triplet kinetics encountered is complex: it depends on temperature, excitation intensity, guest concentration and time. It also depends on the energy interval between $T_{1}$ (guest) and $T_{1}$ (host) and on the transfer efficiencies of the host triplet exciton band