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.

• Received 30 December 1997

DOI:https://doi.org/10.1103/PhysRevB.57.13235