Luminescence and Photoconductivity in Silver Halides

Pulsed and steady-state luminescence and photoconductivity were measured in AgCl and AgBr at low temperatures using x-ray and uv excitation. The luminescence efficiency and electron range (Schubweg) are found to be competitive forms of response as functions of temperature. In AgCl at 4.2^∘{}K electron-hole pairs are captured (or formed) at a luminescence center in about 10^-8 sec, thus accounting for the large decrease of electron range observed at low temperatures. A model is proposed in which an intrinsic luminescence center is represented by a shallow (0.05-eV) electron trap with a characteristic lifetime for radiative recombination after electron capture of about 25 {μ}sec. Similarity to the intrinsic luminescence of alkali halides is noted. Large dark currents of the order of mA and electroluminescence were observed in some crystals after pre-irradiation at 4.2^∘{}K.