Laser generation of transient photocurrents in liquids without the application of an electric field

The first known observation of the Dember effect in liquids is reported using a pulsed nitrogen laser (337.1 nm) which generates photocarriers in a solution of anthracene in tetrahydrofuran. From the sign of the Dember signal (diffusion current), the majority photocarriers are determined to be positively charged anthracene ions. The decay of the Dember signal is exponential. This differs from the second-order decay kinetics reported previously in photoconductivity studies of aromatic molecules in solution. The exponential decay is interpreted as a bimolecular recombination process which includes trapping. The relaxation of the photocarriers is significantly altered when the solution is in contact with the electrodes. The Dember signal has a quadratic dependence on the excitation intensity. The photoionization mechanism is shown to result from at least two competing biphotonic absorption mechanisms, the consecutive absorption of two photons and triplet–triplet annihilation.