First observation of a strongly frequency-dependent photoconductivity

The observation of an ac photoconductivity Phn is reported in the organic charge-transfer complex trinitrofluorenone (TNF). The exponent n is found to increase with decreasing temperature from 0.25 at 300 K to 0.8 at 100 K and saturates at lower temperatures. This result is viewed as a strong indication for a hopping conduction mechanism for photocarriers. The temperature dependence of the exponent n suggests an increasing degree of localization of electron hopping with decreasing temperature. © 1976 The American Physical Society.