The Internal Photoelectric Effect in Crystals

Abstract

THE extensive work of Gudden, Pohl and A others has to a certain extent clarified the behaviour of insulating crystals which become electrical conductors under the influence of light. In these substances the photo-conductivity is entirely electronic, and we leave out of consideration electrolytic processes in which massive ions transport the current. Crystals can in the main be divided into two groups—idiochromatic crystals which are photosensitive in the pure state, and allochromatic crystals which only become photosensitive after being treated with X-rays, or which owe their sensitiveness to the presence of impurities. It has so far proved impossible to correlate these complicated photo-effects with the theory of the solid state, but in view of the recent advances in the theory of poor conductors and of the influence of impurities on conductivity,¹ it seems worth while to see if any unification is now possible.