On the quantum efficiencies of twenty alkali halides in the 12–21 eV region

Abstract

Absolute photoelectric yields of twenty alkali halides have been measured, using a rare gas ion chamber to determine the flux distribution of the He 2 continuum between 12.4 and 21.2 eV. In addition, semiquantitative absorption coefficients were obtained by evaporating AX (alkali halide) films on 300 Å thick Al 2O 3 windows. For most of these materials the photoelectric yield rises to values as high as 0.8 election/ incident photon in the fundamental band beyond the stable exciton region. At photon energies near twice the threshold (or approximately 2 E g the yield often reaches a distinct minimum of the order of 0.4 electron/incident photon. This region is likely characteristic of double exciton production. Beyond 2 E g the yield generally rises to very large values, even over 1.0, strongly implying double excitation processes. Many broad diffuse bands, sometimes well correlated with the absorption coefficients, appear in the electron emission spectrum.