Excitonspektren von Silberhalogeniden und ihren Mischungen

Abstract

The absorption spectra of AgBr and AgCl as well as their mixtures were investigated at liquid oxygen temperature. There are two characteristical features for exciton bands: the terms of the free atoms, and the structure of the crystal lattice. For pure and mixed crystals there exist doublets which can be derived from the terms of the free halide atoms.

The wavelengths of the exciton bands shift linearly with increasing content of AgCl in AgBr. For the first band of the absorption edge this shift is 70 cm⁻¹ per mole percent admixture. The bands shift to a greater extent than they broaden. Thus from statistical calculations can be deduced that there is a region of about 125 anions responsible for an absorption act.

The exciton bands depend considerably on thermal influences from the lattice as well as on distortions resulting from ultraviolet exposure.