Autoionization and Exciton Annihilation in Anthracene

Evidence is presented that the intrinsic carrier generation process in anthracene is one of autoionization (AI) rather than a band-to-band transition. These results are also consistent with the assertion that at least at 6.3 eV, the AI intermediate state is the same, regardless of whether the energy is delivered by a single photon, or by an exciton-exciton process. We have shown that in many cases of “pure” anthracene crystals, there exist impurities that have an effective surface concentration of ∼5 × 10−5 mol fraction, as indicated by exciton quenching properties. These impurities are presumed to be oxygen. The effective exciton lifetime in the surface region is about 5 × 10−9 sec. We have also indicated how the Millikan condenser technique can be used to measure a variety of properties of the exciton.