Time-resolved measurement of excitonic electron emission from a fluoranthene crystal

The emission of an electron is possible with photons of energy below the ionization energy of a crystal, when two photons participate in the electron emission. It has been shown that a combination of two different time-resolved measurements (both with nanosecond laser pulses), i.e. single-electron counting with pulsed excitation and an autocorrelation measurement with excitation by a pair of pulses of varying intervals, enables the identification of the mechanism of biphotonic emission of electrons from a fluoranthene crystal. Ionization via exciton fusion and photoionization has been observed. The mechanism of ionization depends on the excitation energy. This seems to be due to a rather inefficient migration of excitons in this material.