Dynamics of photohole trapping in silver chloride

Abstract

Abstract EPR experiments on photoholes in both AgCl :Cu and AgCl :Pd show the existence of an activation energy barrier, of height near 1.8 meV, in the transition to the localized self-trapped state. The self-trapped hole then migrates athermally via the small-polaron band, for temperatures below 30 K, and by phonon-assisted hopping for temperatures above 35 K. In the hopping régime, the activation energy is 61 meV, suggesting that the binding energy is about 0.1 eV. From the pre-exponential factor, one estimates that the electron transfer integral is about 1% of the energy of the pertinent acoustical phonon. Experiments on AgX:Cu in which 1% of the halide is Br− show that all of the self-trapped holes ultimately migrate to sites with 2 bromide neighbors. Upon annealing, these disappear with complex kinetics and an activation energy of about 180 meV. In AgCl :Pd, Fe, the temperature-dependence of the efficiencies of production of trapped photocarrier centers is determined and correlated with the dynamics of migration of the self-trapped hole and the cation vacancy.