Abstract: By fish gelatin or bovine gelatin as dispersion medium, two nano-sized AgBr/I particle emulsions with different morphology and size were prepared. Photosensitivities of two emulsions increased significantly by the addition of formate as positive hole scavenge dopant, showing formate effective sensitization. It was noted that various formate-doping methods resulted in different sensitized functions. Photosensitivity of the emulsion with homogeneous distribution of formate ions in nano-sized emulsion particle was higher than that of near surface distribution of formate ions in the particle, indicating formate-doping site effect. The multi-structural emulsion particles composed of formate doped core and pure silver halide shell demonstrated approximate photosensitivity as homogeneous formate doped emulsion particles. The addition of sulfur or sulfur-plus-gold into fomate doped nano-sized AgBr/I particle emulsion made photosensitivity further increased, which presented a synergetic effect of formate sensitization with conventional sulfur or sulfur-plus-gold sensitization.

Key words: formate, dopant of trapping positive holes, nano-sized silver halide paricles, chemical sensitization