Intrinsic Photoconductivity in the Alkali Halides

Photoconductivity in thin films of RbI, KBr, and KCl has been measured at temperatures of 10 and 80^∘{}K in the spectral range from 5.5 to 10 eV. The Schubweg of the photoelectrons and the yield of photoelectrons per incident quantum were determined. In the case of RbI the data tend to confirm the existence of exciton states lying between the two components of the familiar spin-orbit doublet, as was recently suggested by Fischer and Hilsch. It is estimated that the band gaps of RbI, KBr, and KCl are 6.37, 8.0, and 8.7 eV, respectively.