silverhalogenid

Silver halides are inorganic compounds with the general formula AgX, where X is a halide ion (chloride, bromide, or iodide; silver fluoride exists but is less common in practical uses). They appear as pale crystalline solids that are sparingly soluble in water. They can be prepared by precipitating silver salts with solutions containing halide ions and are typically formed as fine crystals dispersed in a gelatinous medium for photographic use.

They are notably photosensitive. When exposed to light, silver halide crystals undergo a photochemical reaction in which electrons reduce Ag+ ions to metallic silver, forming a latent image within the crystal lattice. In most photographic processes, chemical developers reduce the exposed silver halide to metallic silver, creating a visible image, while unexposed crystals are removed by fixing.

In photography, silver halides are the essential light-sensitive component of traditional film and photographic paper emulsions. The halide composition and crystal size influence sensitivity, contrast, and spectral response. AgCl is relatively sensitive to blue light, bromide-rich emulsions are widely used for their good sensitivity and grain characteristics, and iodide additions can increase speed and affect spectral response. Modern practice often uses mixed AgBr/AgI emulsions with sensitizers to broaden sensitivity and improve performance.

Beyond conventional photography, silver halides are used in radiographic films and other archival imaging materials. They are typically formed by precipitation from silver nitrate solutions with halide salts and then embedded in binders such as gelatin to create a stable, photosensitive layer.