The influence of phase boundaries on the photoelectron lifetime of T-grain emulsion crystals is examined with the microwave absorption method. For the measurements, AgBr_1−xI_xT grains with a core-shell and a so-called “gradient” structure were used. The core-shell ratio, the grain volume, and the iodide content of the core were varied. The microwave absorption measurements indicated that a maximum photoelectron lifetime can be reached for a special combination of these parameters. In the case of core-shell T grains, maximum values were found for a core-shell ratio of 1:1 and iodide contents x > 0.08. For iodide values x < 0.02 “gradient” grains lead to the highest photoelectron lifetimes. A model is proposed to explain the behavior of the structured grains influenced by the interplay of the geometrical grain structure and the iodide content.