PHOTOIONIZATION, ELECTRON-TRAPPING AND PHOTOCONDUCTION IN GLASSES.
BRANDEIS UNIV WALTHAM MASS
Pagination or Media Count:
Photoionization and electron-trapping in glassy media, using spectrophotometric and conductimetric techniques is described. Aromatic anions mono- and di-negative ions of naphthacene were selected as the systems for study because of their low ionization potentials, slow back reactions and known spectra of the ions and parent hydrocarbons. The glassy solvent was 2-methyltetrahydrofuran 2-MTHF at liquid N2 temperature. Using chemical actinometry, quantum yields for the overall photoionization and electron-trapping process were measured for both naphthacene ions. A new effect was observed, in which the photothreshold of platinum or stainless steel electrodes was shifted from below 2600 A to about 5000 A, as a result of contact with naphthacene dianion. The observed phenomena, including effects of intensity, exposure time, photovoltaic behavior and reversed photocurrents, can be consistently interpreted on the basis of simultaneous electrode and volume ionization processes, combined with space-charge effects. These latter complications arise from the differential rates of diffusion of negative and positive carriers, and from finite electron-trapping energies.