Spectral shift and degradation in photoemissive thin films

Photocathode degradation in camera tubes may result from high current density operation of the photoemissive thin film. Some aspects of the various mechanisms causing loss in sensitivity and shift in spectral response are discussed. Among these are positive ion bombardment of the film, localized heating of the photosensitive film, and solid-state ion transfer from the supporting substrate into the photosensitive film. The types of photoemissive films studied are tin oxide undercoated S-11, S-20, modified S-1, and high temperature bi-alkali photocathodes.