Photoemission from an Anthracene Single Crystal Doped with Alkali-Metals

Abstract

External Photoelectric effect is investigated with an anthracene single crystal doped superficially with alkali-metals; cesium, potassium and sodium. The threshold energy is found to be dependent upon the amount of metal doped. When the doping amount is low, the photoelectrons are excited via the first singlet exciton state and are emitted with the aid of the surface double layer formed between alkali-metal and anthracene. The photoemission yield of a highly doped crystal shows a cubic law dependence upon the incident photon energy. The threshold energy, 2.57 eV, obtained in this case can be interpreted as the energy of surface state below the vacuum level.