The drift mobilities of electrons and holes in anthracene crystals have been measured using a pulsed photoconductivity technique. The mobilities found at room temperature vary from about 0.3 ${\mathrm{cm}}^2$/volt sec to about 3 ${\mathrm{cm}}^2$/volt sec, depending on the crystal orientation, and the mobilities increase as the temperature is lowered. The wavelength dependence of the number of charge carriers produced by a pulse of light, as well as other experimental data, indicates that the charge carriers are not produced in the interior of anthracene crystals, but that they are released from a surface layer of the crystal either directly by photons or by excitons which migrate to the surface.

• Received 15 April 1960

DOI:https://doi.org/10.1103/PhysRev.119.1226