Optical properties of mixed silver halide crystals and fibers

The dependence of the bulk (β_b) and surface (β_s) absorption coefficients of AgCl_xBr_1-x crystals and of polycrystalline fibers at 10.6 μm on the composition (x) of the material were investigated. The bulk coefficient β_b for AgBr was about 0.5×10^-4 cm^-1 and increased gradually with increasing molar concentration x of the Cl^- ions up to 2.5×10^-4 for pure AgCl crystals. Luminescence properties of these crystals as well as effects of thermal treatments on the absorption, luminescence, and conductivity were also investigated. A correlation was found between the effects of these treatments on the infrared (IR) absorption, the luminescence, and conductivity of the various samples. Experimental results indicate that the absorption of the silver halide crystals at 10.6 μm is mainly due to cation vacancies bound to dislocations. The absorption of the fibers was found to be greater than that of the crystals of the same composition. This is apparently due to defects induced by the heating under pressure, applied during the production of the fibers by extrusion, and the subsequent fast quenching to room temperature. A simple method for reduction of the IR absorption is proposed.