Exciton–charge carrier interactions in the electroluminescence of crystalline anthracene

Abstract

The interactions of triplet excitons with trapped charge carriers are studied in anthracene single crystals. The triplet excitons are generated by the recombination of charge carriers through double injection. The lifetime of the triplet excitons is studied from the decay of the phosphorescence intensity in a transient measurement. The interaction rate constant for the trapped charge carriers is of the same order of magnitude as previous published data measured with single injection of electrons. It is further shown that the rate constant varies with different conditions of crystal growth. The simultaneous investigation of double injection delayed fluorescence reveals also a strong quenching of the delayed fluorescence from the excited singlet state by trapped charge carriers. Magnetic field measurements show that this quenching is partly due to an increased dissociation of the triplet pair state through the presence of charge carriers. The possibility of enhanced spin relaxation of the triplets in the pair state is also discussed.