Intermolecular energy transfer between the individual zero-field levels of triplet traps in an orientationally disordered solid

Abstract

Abstract : The zero-field transitions and levels of the phosphorescing triplet state of the traps in the orientationally disordered crystal of 1-bromo-4-chloro-naphthalene (BCN) are assigned by using phosphorescence-microwave double resonance techniques at 1.8 K. The relative population of the different zero-field levels are determined at different delays after singlet-singlet excitation and as a function of the energy of the emitting traps within the inhomogeneously broadened bands. For the same delay, the population of the radiating level is found to have a maximum which is at a lower energy within the inhomogeneous profile than that for the dark level. This observation is contrary to predictions based on one-dimensional exchange mechanisms and might suggest the involvement of dipole-dipole coupling for the triplet-triplet energy migration at the relatively large distances involved in the energy transfer between the traps. Originator-supplied key words include: Energy transfer, Mechanisms, Zerofield levels and Optical detention.