Fosforescent

Fosforescent, commonly spelled phosphorescent in English, describes materials that continue to emit visible light after the illumination source has been removed. This afterglow results from electrons in the material remaining in excited, long‑lived states before slowly returning to the ground state.

The mechanism involves trapping of excited electrons in defect or dopant sites within a crystal lattice. When these trapped electrons are released gradually, they emit photons over an extended period. This slow release differentiates phosphorescence from fluorescence, in which emission ends almost immediately when the excitation stops.

Common fosforescent materials include zinc sulfide doped with copper (ZnS:Cu), known from older glow‑in‑the‑dark items, and strontium aluminate doped with europium and dysprosium (SrAl2O4:Eu,Dy), which provides brighter light and longer afterglow lasting hours under suitable charging. Researchers explore various host lattices and dopants to tune color, brightness, and persistence. Particle size, environmental exposure, and charging methods also affect performance.

Applications span safety and emergency signage, glow‑in‑the‑dark components for watches and toys, decorative coatings, and certain sensing or imaging techniques in research contexts. However, biocompatible and low‑toxicity phosphors are active areas of study for potential medical uses, with attention to material safety and environmental impact.

Historically, early phosphorescent materials were metal sulfides discovered in the late 19th and early 20th centuries. The development of long‑lasting afterglow in the 1990s, especially with strontium aluminate formulations, significantly expanded practical uses and commercial availability.