Optical and photochemical properties of some halides and their complexes.

The studies described in this thesis have been placed under three headings: some properties of silver-iodide complexes, centres found in silver halides, and a discussion of confined electron centres including the F-centre in alkali halides. The introduction includes a discussion of some properties of the solid state and the principles of the experimental methods used - details of which are given in chapter two. Studies on the silver-iodide complexes are reported in section 3.1. In dilute solutions of silver and alkali iodides in organic solvents, absorption bands occur at c.230 mu and C.310 mu, and are attributable to the species AgI2 and Ag[.;I.;" respectively. Thediffuse reflectance of the solid complexes are also reported. Further, preliminary electron spin resonance studies of the gamma irradiated solid complexes are reported. In section 3.2, it is demonstrated that the centres in irradiated silver halides which give rise to a conduction electron spin resonance cannot be silver particles. Gamma irradiation at low temperatures does not seem to give rise to simple paramagnetic colour centres as in the alkali halides. Gyanine dyed silver halides, illuminated at low temperature, show a single electron spin resonance, with a g-value slightly dependent on the halide. The results of Stasiw on chalcogen doped silver halides are discussed and some experimental studies are reported. In section 3.3, magnetic resonance data on the F-centre (from the literature) is analysed to show the dependence of the density of the unpaired electron in orbitals of near neighbour cations on various parameters of the alkali halide. In particular this density is seen to decrease linearly with increasing halide (cavity) radius and increase with the covalent radius of the alkali metal. The importance of cavity size is stressed and implications for any theory of the P-centre are discussed. Some measurements of the absorption of iodide doped crystals are presented.