Optical properties of silver halide fibres: Ageing effects

The relation between the structure of fibres extruded from mixed silver halides AgBr_1-xCl_x and their IR optical losses and luminescence properties is studied. The recently established ageing effect of the considerable growth of mean grain size of the fibre's polycrystalline structure (typically from 20 to 1000 nm in two years) is correlated with IR and luminescence measurements. IR spectra measured in the interval 3.0-13 μm show growth of the concentrations of molecular impurities. The luminescence measurements are used for the characterization of the fibre's structure ordering. The luminescence decay kinetics is analysed theoretically in terms of the diffusion-controlled recombination of spatially well-correlated Frenkel defects. The considerable difference between the diffusion properties of monocrystals and fibres is established. This is caused by partial disorder (the grain structure effect) of the initially polycrystalline structure arising due to the fibre extrusion.