Photoelectric Effects in the Silver Halides

Abstract

Measurements have been made of quantum yield for external photoemission from pure and doped silver halides and from samples with various surface preparations. Energy distribution curves for external photoelectrons were simultaneously determined. The quantum yield for external photoemission was found to rise smoothly from a threshold of about 6.2 eV to a yield of about 0.1 electrons per incident photon near 11-eV incident energy for pure AgCl. The bulk of external photoelectrons were found to emerge with a uniform distribution in energy between 0 and 2 eV for all incident energies (in contrast to alkali-halide results) with the exception of a small tail which moves in proportion to increasing incident energy. Only a slight indication of the onset of band-to-band scattering was found. Models to account for these results in terms of multiple electron-electron scattering, nonvertical transitions, and the contribution of the second valence band are discussed in light of the recent theoretical band scheme for the silver halides. Surface treatment and dopings of ${\mathrm{Cu}}^{+}$ and ${\mathrm{Ni}}^{+}$ (significant in terms of photographic and photoconductive effects) were found to have little effect on intrinsic photoelectric properties of AgCl.