Knowledge Bank

The fluorescence spectrum of solid-state polyvinyl carbazole (PVCA) is of the excimer type whereas in solution both mirror-image and excimer-fluorescence spectra can be observed. The excimer-fluorescence decay time after flash excitation was found to be approximately $4\times 10-8$ sec. Small amounts of perylene, hexachloro-p-xylene, and trinitro fluorenone in PVCA reduce the quantum efficiency (y) of the PVCA fluorescence but leave the decay time unaffected. The quenching factor $Q=yo/y(c)-1$ depends linearly on the guest concentration (c). The results are interpreted in terms of energy transfer by monomer-exciton diffusion involving two competitive traps: excimer forming sites and guest molecules.