Fosforescera

Fosforescera is the property by which certain materials emit light after being excited by an external energy source and continue to glow after the excitation ends. This phenomenon, commonly called phosphorescence, differs from fluorescence in that the light emission persists for a noticeable time due to the involvement of metastable electronic states.

Mechanism: during excitation electrons are promoted to higher energy levels and can become trapped in defect or impurity states within the material. The release of these trapped charges to lower-energy states occurs slowly, often via spin-forbidden transitions, producing photons over milliseconds to hours.

Materials: inorganic phosphors such as zinc sulfide doped with manganese, and strontium aluminate doped with europium and dysprosium are well-known for long afterglow. Organic phosphorescent compounds and persistent-luminescent composites have expanded with flexible and printable formulations. Persistent luminescence materials can store energy from light, mechanical stimulation, or other energy inputs and release it gradually.

Applications: safety signage and emergency egress markers, glow-in-the-dark products, watches and novelty coatings, anti-counterfeiting inks, and specialized research tools in optoelectronics and bioimaging under controlled conditions.

History and terminology: the phenomenon has been observed for centuries and has been studied extensively since the 19th and 20th centuries. In Italian usage, fosforescera is sometimes encountered as a verb form describing the act of phosphorescing, while fosforescenza is the common noun for the effect.