PHOTOCURRENT INDUCED BY DETRAPPING OF CHARGE-CARRIERS TRAPPED BY RADICALS IN NAPHTHALENE AND ANTHRACENE SINGLE-CRYSTALS

Photocurrent spectra induced by detrapping of charge carriers trapped by neutral radicals in naphthalene and anthracene crystals have been studied. One broad band around 700 nm in naphthalene and two broad bands around 800 nm and 900 nm in anthracene were observed. It was shown that the broad bands in each crystal involve transitions of carriers trapped by a single trap. Studies of the effect of the polarity of injected carriers on detrapping photocurrent indicated that the broad band for naphthalene is induced by electrons and that for anthracene is by holes. A molecular orbital calculation of the positive and negative l-hydronaphthyl ions was made. The lowest transition energies of these ions were found to be larger than the photocurrent-band energy. This result together with the fact that the band is broad, leads us to a conclusion that the observed photocurrent band is due to the transfer of charge trapped at the neutral radical to the host molecules.