DISLOCATIONS AND DONOR CENTERS IN SILVER-HALIDE EMULSION GRAINS

The involvement of dislocations and donor centres in the technology of high-performance, negative surface-imaging emulsions with monodispers e, regular hexagonal,thin tabular grains is discussed. In core/shell a nd core/annular zone/shell structures, narrow prismatic edge dislocati on half-loops, extending through the annular zone and outer shell from the interfaces to the lateral edges, are introduced to partially rela x lattice strains resulting from halide ion concentration gradients. T he sites of termination of these dislocations provide local areas of e nhanced surface reactivity or dislocation sensitivity centres. Sensiti zing Ag2,Ag2O and Ag2S donor centres are introduced within the grains and on the outer surface. Sensitizing (Ag,Au)S donor centres are confi ned to the outer surface and preferentially formed at the sensitivity centres where they are associated with Ag2 donor molecules also functi oning as latent image growth nucleus precursors. The formation of such Ag2 molecules along internal dislocation lines is largely prevented b y growth of the interfacial volume under oxidizing conditions. The pho toaggregation theory is used throughout for the discussion of the proc esses of emulsion technology and of the formation of development centr es during exposure from silver and gold atoms equivalent to sensitizin g donor centres.