Process for doping silver halide emulsion grains with Group 8 transition metal shallow electron trapping dopant, selenium dopant, and gallium dopant, and doped silver halide emulsion

This invention relates to a method for preparing silver halide emulsions incorporating gallium, selenium, and Group 8 shallow electron trapping dopants, and to the resulting doped emulsions and photographic elements which contain one or more of such doped emulsions. A process for incorporating dopants in a silver halide emulsion is described comprising precipitating silver halide emulsion grains in a reaction vessel, wherein at least one gallium dopant, at least one Group 8 metal dopant, and at least one selenium dopant are introduced into the reaction vessel during precipitation of the silver halide grains; where the gallium dopant is introduced in the form of a gallium halide coordination complex of the formula (I):wherein R represents a lower alkyl group of from 1-3 carbon atoms; X is Cl, Br, or I; and x is from 1-3, y is from 1-3, and x+y=4; and the Group 8 metal dopant satisfies the formula (II):wherein n is −2, −3 or −4; M is a Fe, Ru, or Osion; and Lrepresents bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand. In another embodiment, this invention is directed towards silver halide emulsions formed by such process. In a still further aspect, this invention is directed towards a photographic element comprised of a support, and a silver halide emulsion layer coated on the support comprised of an emulsion obtained by the process of the invention.