Fosforescenssi

Fosforescenssi is the long-lasting emission of light from a material after it has been excited by an external energy source, a phenomenon roughly equivalent to phosphorescence. Unlike fluorescence, fosforescenssi can persist for milliseconds to hours after the excitation is removed.

The mechanism involves trapping of charge carriers at defects or dopants within a material. After light absorption, electrons may become trapped in metastable states and are released slowly, emitting light as they recombine. This often requires a transition to a triplet state and radiative decay. Materials exhibiting fosforescenssi include inorganic phosphors, doped crystals, and some organic compounds; the lifetime and brightness depend on temperature and the surrounding environment.

Fosforescenssi occurs in engineered materials such as glow-in-the-dark pigments, phosphor coatings, and safety signage, as well as in some naturally occurring minerals. It is important to distinguish it from chemiluminescence, which arises from a chemical reaction, and from fluorescence, which decays almost immediately after excitation.

Applications span emergency lighting, safety and decorative coatings, and potential use in bioimaging with long-lived emitters. Characterization typically uses time-resolved photoluminescence to measure spectral properties, emission intensity, and decay lifetime. The term is common in Finnish-language sources, while internationally the same physical process is usually described simply as phosphorescence. As a concept, fosforescenssi covers the same family of long-lasting luminescent materials studied across disciplines.