Charge-transfer Exciton State and Ionic Energy Levels in Anthracene Crystal

Abstract

By means of external electron emission produced by double-exciton annihilation inside anthracene crystal, evidence is produced for the existence of a charge-transfer (CT) exciton in anthracene at 3.45 eV, with a lifetime conjectured to be 2 × 10⁻⁷ sec. The efficiency of generating the CT exciton increases markedly at an incident light energy greater than 4 eV. This value is associated with that of an upper conductivity band. The lowest conductivity level in anthracene must be larger than 3.45 eV, and is estimated to lie at 3.7 eV. Delayed fluorescence produced by α-particle bombardment of anthracene is discussed in terms of CT excitons.