It is known in photography that silver halide grains are useful informing developable latent images when struck by actinic radiation, such as electromagnetic radiation. The use of silver bromide, silver chloride, silver iodide, and combinations of these metal halides into crystals have been widely used in photographic products.
In the formation of color photographic products both for color negative film, transparencies, and color paper, there has been a continuous improvement in the properties of these materials, particularly in their speed and fine grain properties.
However, there remains a need for such materials that have higher contrast, lower fog, and improved reciprocity over wide exposure ranges.
As shown in Research Disclosure, December 1989, 308119, Sections I-IV at pages 993-1000, there have been a wide variety of dopants, spectral sensitizers and chemical sensitizers proposed for addition to emulsions of gelatin and silver halide grains or crystals. These materials have been proposed for addition during emulsion making as dopants or after emulsion formation as sensitizers. However, there remains a continued need for an improvement in the use of such materials to obtain better photographic performance.
U.S. Pat. No. 4,933,272 by McDugle et al discloses formation of silver halide grains exhibiting a face centered cubic crystal lattice structure internally containing a nitrosyl or thionitrosyl coordination ligand and a transition metal chosen from groups 5 to 10 inclusive of the periodic table of elements. These complexes play a significant role in modifying photographic performance.
U.S. Pat. No. 4,806,462 by Yamashita et al, at column 4, discloses formation of silver halide photographic material that may be doped with a variety of metals including magnesium, calcium, barium, aluminum, strontium, rheuthium, rhodium, lead, osmium, iridium, platinum, cadmium, mercury, and manganese.
However, there remains a need for improved photographic products that have a sharper toe (higher contrast) at low exposures while maintaining reciprocity during exposure. There is particular need for color print materials that have these properties.