Photoelectric Effects in Certain of the Alkali Halides in the Vacuum Ultraviolet

An extensive search for internal photoconductivity in NaCl, KCl, KI, and LiF resulting from stimulation by light of wave-length lying below the fundamental absorption edges of these crystals has yielded negative results. Photon energies employed ranged from about 6 ev to 21 ev. Calculations based on observed external photoelectric emission currents indicate that photoelectric quantum efficiencies as low as ${10}^{-8\mathrm{}}$ electron per incident photon could have been detected if electrons traveled completely through the crystal.