Patent ID: 7157219

Claim:
A method of preparing a photothermographic emulsion comprising: (A) providing a dispersion of a preformed photosensitive silver halide grains and a non-photosensitive source of reducible silver ions, (B) providing one or more sulfur-containing compounds that is a diphenylphosphine sulfide compound, in association with said preformed silver halide grains and said non-photosensitive source of reducible silver ions, said diphenylphosphine sulfide compound being represented by the by the following Structure PS: wherein Ph 1 and Ph 2 are the same or different phenyl groups, R 1 and R 2 are independently hydrogen or an alkyl or phenyl group, L is a direct bond or a 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, and sulfur atoms in the chain, (C) chemically sensitizing said preformed silver halide grains by decomposing said diphenylphosphine sulfide compound on or around said silver halide grains in an oxidizing environment to provide sulfur chemically sensitized photosensitive silver halide grains in reactive association with said non-photosensitive source of reducible silver ions, and (D) providing a gold(III)-containing compound in association with said preformed silver halide grains and said non-photosensitive source of reducible silver ions to provide gold(III) chemically sensitized photosensitive silver halide grains in reactive association with said non-photosensitive source of reducible silver ions, said gold(III)-containing compound represented by the following structure GOLD: Au(III)L′ r Y q (GOLD) wherein L′ represents the same or different ligands, each ligand comprising at least one heteroatom that is capable of forming a bond with gold, Y is an anion, r is an integer of from 1 to 8, and q is an integer of form 0 to 3, the molar ratio of said gold(III)-containing compound to said sulfur-containing compound used in the chemical sensitization is at least 1:1.