persistentluminescence

Persistent luminescence, also called afterglow, is light emission that continues after excitation has ended. It differs from fluorescence by its extended duration, which can last from minutes to hours depending on material and conditions.

In inorganic phosphors, a host lattice is doped with activator ions (for example Eu2+, Dy3+). Illumination creates charge carriers that become trapped at defects. When these traps release carriers over time, they recombine at activator centers and emit light. Trap depth, dopant concentration, and temperature govern persistence and brightness.

Common persistent phosphors include SrAl2O4:Eu2+,Dy3+ and CaAl2O4:Eu2+/other lanthanides; BaSi2O2N2:Eu; among others in oxide, silicate, and nitride families. Emission color is set by the activator, with green or blue afterglows typical.

Applications include safety signage, luminous watches and instrument dials, novelty paints, and optical sensing. Long-lived emission is also explored in bioimaging and anticounterfeiting. Some systems support photostimulated luminescence or thermoluminescence readout, enabling information storage or erasure.

Research aims to extend persistence, brightness, and color range, and to develop nanostructured or flexible materials for new uses.