EXTERNAL PHOTOEMISSION BY SINGLET-EXCITON PHOTOIONIZATION IN AN ANTHRACENE SINGLE-CRYSTAL

The external photoemission by singlet-exciton photoionization has been observed in anthracene single crystals with two-color, two-step excitation. One laser pulse (360 or 420 nm) generates singlet excitons and the photoemission occurs by the second laser pulse of longer wavelength (460-540 nm). The threshold energy of the photoemission has been found to be 5.5 eV and is insensitive to the energy of the first-step excitation. This indicates that the external photoemission occurs through the photoionization of a relaxed singlet exciton. The threshold energy of the photoemission via exciton photoionization (5.5 eV) is lower than that of the conventional photoemission with one-photon excitation (5.75 eV). © 1990.