Phonon termoactivated exciton tunneling in crystals of weak charge transfer complexes N-TCPA doped with Nd8-TCPA Original Research Article

An analysis has been made of strong exciton phosphorescence quenching observed in pure crystals of weak charge transfer (CT) complexes naphthalene-tetrachlorophthalic anhydride (N-TCPA) as well as in those doped with deuteronaphthalene-tetrachlorophthalic anhydride (Nd8-TCPA) (6%) when the temperature is increased from 1.4 to 4.2 K. Quenching of the exciton luminescence in these crystals is due to exciton trapping. A model of triplet excitons migrating along the one-dimensional (1D) chain with traps and 100 cm−1 energy barriers has been suggested. The barriers are formed in crystals by the triplet state of the Nd8-TCPA molecules. In this temperature range the main mechanism of exciton passing the barriers is tunneling. The temperature dependence of exciton rate of barrier passing (W) has been obtained. Effects of the barrier shape and width on W(T) have been considered. This experimental dependence was fitted to the calculative curves and satisfactory agreement has been achieved if one assumed that low-frequency phonons (25 cm−1) participated in exciton tunneling.