Generation of Charge Carriers in Anthracene with Polarized Light

Intrinsic photogeneration of charge carriers in anthracene .1-4 single crystals occurs with photon energies in excess of 4 eV The mechanism of this process, however, is not well understood. The interpretation of the wavelength dependence of this current in 2 £\ particular is difficult. Two maxima in the photocurrent appear, <sJLJ one at 4.4 eV ' ' and the other at 5.4 eV. The 4.4 eV maximum appears in a region of low absorption coefficient (k ~ 16,000 cm ) -1 and the other maximum in wavelength region where k ~ 113,000 cm . It has been proposed that bulk generation of carriers in anthracene proceeds by direct excitation Into a conduction band. On this basis an Inverse dependence on k of the bulk generated photocurrent was predicted, ' which seems to explain the wavelength dependence of 5 2 the 4.4 eV maximum, but not that of the 5.4 eV peak. In order to ascertain the dependence of the bulk generated photocurrent on k we studied the relative quantum efficiency of the photocurrent at fixed wavelength as a function of the angle 6 between the electric vector of -ate polarized light and the b crystalline axls.<^he extent of variation of k with 9 depends on the wavelength, being