Longafterglow

Longafterglow is a property of certain luminescent materials that continue to emit light for an extended period after the excitation source is removed. It is often described as persistent luminescence or long-persistence afterglow, and it contrasts with fluorescence, which decays in a fraction of a second, and with ordinary phosphorescence that fades relatively quickly. In longafterglow materials, energy from external light is stored in defect-related trap states within the host lattice and is released slowly as photons over time.

Many longafterglow phosphors belong to doped host lattices. A well-known example is strontium aluminate doped with europium and dysprosium (SrAl2O4:Eu2+,Dy3+), which can glow for hours after charging under UV or visible light. Other compositions employ different host materials and dopant ions, such as calcium or zinc-based lattices with rare-earth dopants like Eu2+/Dy3+, Ce3+/Tb3+, or Mn2+. The common mechanism involves trap levels created by dopants that capture charge carriers during illumination and release them gradually, sustaining emission long after the stimulus ends.

Applications of longafterglow materials include glow-in-the-dark signage, emergency exit markings, toys and novelty items, watches and dashboards, and architectural or artistic lighting. Performance depends on the charge dose, temperature, and material composition; brightness fades over time and typically requires recharging by exposure to light. Ongoing research aims to improve efficiency, safety, color variety, and duration, exploring new host lattices and dopant combinations to extend persistence and reduce production costs.

Related terms include persistent luminescence and phosphorescence, which describe overlapping but distinct concepts in luminescent science.