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 ${10}^{-8\mathrm{}}$ 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 μsec. 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.