Indirect optical absorption and radiative recombination in silver bromoiodide

The low-temperature (4.2 K) and room-temperature absorption spectra of several AgBr_1-x{I}ₓ$ (x=0--0.25) samples have been obtained. Conventional analysis of these spectra yields the band-gap energy (${E}g$), which decreases with iodide content. The band-gap energies at 4.2 K range from 2.684 eV for pure AgBr to 2.448 eV for ${AgBr}0.75I0.25. The more accurate band-gap information is used to estimate the trap depth of the acceptor states observed in the low-temperature emission. Data indicate that both donors and acceptors are shallow traps in AgBr_1-x{I}ₓ$ systems.