Solarization (physics)

Solarization, in the context of physics, specifically refers to a phenomenon observed in certain materials, primarily photographic emulsions and semiconductor devices, where prolonged or excessive exposure to light leads to a decrease in the observed effect expected from light exposure. This is counterintuitive as one would typically expect increased exposure to result in a stronger effect.

In photographic emulsions, solarization describes the reversal of the image obtained on a photographic film or plate. Normally, exposure to light causes the silver halide crystals in the emulsion to form metallic silver upon development, resulting in a darkening of the image. However, with extreme overexposure, a partial reversal occurs; areas that received the most light may become lighter than areas that received less light. This effect is different from the Sabattier effect, which also produces image reversal but involves a brief secondary exposure during development, whereas solarization occurs solely due to extreme overexposure prior to development. The exact mechanism behind photographic solarization is complex and involves the formation of internal silver nuclei within the silver halide crystals, which compete with the surface nuclei formed during normal exposure. These internal nuclei hinder the development process at the surface.

In semiconductor devices, particularly certain types of photodetectors, solarization can manifest as a decrease in photosensitivity after prolonged or intense illumination. This can occur due to light-induced changes in the material's structure or properties, such as the creation of defects or changes in the carrier concentration. These changes affect the device's ability to efficiently convert light into an electrical signal. The mechanisms responsible for solarization in semiconductors are material-dependent and can include processes like the Staebler-Wronski effect in amorphous silicon or the creation of persistent photoconductivity effects.