silverhalide

Silver halides are inorganic compounds consisting of silver ions paired with a halide anion, with the general formula AgX where X is Cl−, Br−, or I−. They form as small, highly insoluble crystals and are typically prepared by reacting a soluble silver salt (such as AgNO3) with a soluble halide source (such as NaCl, NaBr, or KI), yielding precipitated AgX that is collected and washed.

A defining characteristic of silver halides is their light sensitivity. When exposed to light, the silver ions within the crystal lattice are reduced to metallic silver, creating latent image centers that can be amplified during chemical development. In photographic processing, exposed grains are reduced by a developer to form a visible image, while unexposed grains are removed by a fixer that dissolves residual AgX via complexation (commonly with thiosulfate). This combination underpins traditional photographic film and paper.

The three common halides differ in color, solubility, and sensitivity. AgCl is white and relatively insoluble; AgBr is pale cream and more light-sensitive; AgI is yellow and highly photoresponsive, though less stable and more costly in practice. Modern photographic emulsions typically use mixtures of AgBr with small amounts of AgCl, sometimes with sensitizing dopants to improve speed and spectral response.

Beyond photography, silver halides are investigated for sensors, radiation detectors, and chemical studies of photoinduced processes. Their chemistry is also relevant to qualitative analysis and the stabilization of halide-containing materials.

In summary, silver halides are moisture-sensitive, light-sensitive ionic solids whose photochemical behavior makes them central to traditional imaging technologies, with fixed and solvent-accessible reactions that enable development and fixing of photographic images.