Luminescence and ODMR studies of X-traps for triplet excitons in organic crystals

The excited triplet states of shallow X-traps in neat single crystals of 4,4'-dichlorobenzophenone were studied at liquid helium temperature by luminescence spectroscopy and magnetic resonance with optical detection. The vibrational phosphorescence bands, the polarization of phosphorescence spectra, and the triplet zero-held splitting parameters of these traps have been analyzed. A specific model of the structure defect (a molecule is turned by 180 degrees on its long axis) has been considered in organic crystals of benzophenone type which consist of molecules whose dipole moments compensate each other in a unit cell. The calculated depth of such a dipole X-trap for triplet excitons in Lf,4'-dichlorobenzophenone crystals at the account of a defect molecule relaxation upon its slewing was found to be comparable with the experimental one. (C) 1997 American Institute of Physics.