Defects and the photographic process

The high imaging efficiency of today's color negative film depends on the u nique defect properties of silver halides. We have chosen two important def ect topics to highlight: defect-induced anisotropic crystal growth, and sha llow electron trapping at surface defects and transition metal dopant sites . High imaging efficiency depends on the ability to concentrate photoelectr ons and thereby to form a single latent image center per crystallite. This requires electron localization at a partially-charged, shallow electron tra p at the surface followed by a shallow-deep transition to a metastable atom state. Subsequent ionic and electronic trapping processes that build the l atent image occur only at this site. In some cases, doping the bulk of the microcrystal with extrinsic shallow electron traps can improve latent image formation efficiency. Electron concentration does not occur at these dopan t sites since they are not partially charged. Magnetic resonance and photo- conductivity studies of the dynamics of shallow trapping by dopants and of the shallow-deep transition at surface sites are presented.