Interactions between self- and solute trapping of photocarriers in Pd-doped AgCl

EPR studies on ultraviolet-irradiated crystals of AgCl: Pd have confirmed earlier results on AgCl: Cu for the existence of an energy barrier in the self-trapping of the photohole. The height of this barrier is near 1.8 meV. Migration of the self-trapped hole was found to be athermal for temperatures below 30 K; above 35 K the self-trapped hole hops, with a diffusivity given by D=7×10^-7exp(-61 meV/kT) cm²/sec. This suggests that the value of the electron transfer integral is about 1% of the energy of the phonons involved, that the bandwidth for the self-trapped hole is of the order of 2 meV, and that the binding energy of the hole is approximately 0.1 eV. The dependence on temperature of the efficiency of photoproduction of various trapped-carrier palladium centers was determined, and was correlated with the migration of the self-trapped hole. The presence of a small amount of Fe²⁺ "tracer" served to indicate those decay processes that were due to thermal release of trapped holes.