Patent ID: 7087366

Claim:
A method of preparing a photothermo-graphic emulsion comprising: (A) providing a photothermographic dispersion of preformed photosensitive silver halide grains and a non-photosensitive source of reducible silver ions, and performing the following steps in order, (B) providing one or more diphenylphosphine sulfide compounds, in association with said preformed photosensitive silver halide grains and the non-photosensitive source of reducible silver ions, said diphenylphosphine sulfide compound being represented by the following Structure PS: wherein Ph 1 and Ph 2 are the same or different phenyl groups, R 1 and R 2 are each independently hydrogen or an alkyl or phenyl group, L is a direct bond or a divalent linking group, m is 1 or 2 and when m is 1, R 3 is a monovalent group and when m is 2, R 3 is a divalent aliphatic linking group having 1 to 20 carbon, nitrogen, oxygen, or sulfur atoms in the chain, (C) chemically sensitizing said preformed photosensitive silver halide grains by decomposing the diphenylphosphine sulfide compound represented above by Structure (PS) on or around said preformed photosensitive silver halide grains in an oxidizing environment to provide a photothermographic emulsion comprising chemically sensitized preformed photosensitive silver halide grains in reactive association with said non-photosensitive source of reducible silver ions, and (D) converting some of said reducible silver ions in said non-photo-sensitive source of reducible silver ions into photosensitive silver halide grains.