Strongly enhanced optical absorption in quench-deposited amorphous AgI films

Amorphous AgI films prepared by quench deposition are characterized by markedly stronger optical absorption than crystalline films, by a factor more than ten in the exciton transition-energy region. They crystallize in the zinc-blende structure exhibiting well-defined crystallization temperatures dependent on the thicknesses, from 220 K (thick) to 180 K (thin). The strong absorption in the amorphous state cannot be explained by the familiar relaxation effect of the k-conserving selection rule, suggesting a fundamental change in the short-range order due to amorphization. Under the new short-range order, a considerable amount of the metal d electrons take part in low-energy optical absorption together with the I p electrons, due to p-d hybridization.