Persistent luminescence
Encyclopedia
Commonly referred as phosphorescence, persistent luminescence is the phenomenon encountered in materials which make them glow in the dark after the end of an excitation
with UV or visible light.
and phosphorescence
(see for definitions and ). Indeed, in fluorescence, the lifetime of the excited state is in the order of a few nanoseconds and in phosphorescence, even if the lifetime of the emission can reach several seconds, the reason of the long emission is due to the deexcitation between two electronic states of different spin multiplicity. For persistent luminescence, it has been known for a long time that the phenomenon involved energy traps (such as electron or hole trap) in a material which are filled during the excitation. After the end of the excitation, the stored energy is gradually released to emitter centers which emit light usually by a fluorescence-like mechanism.
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
with UV or visible light.
Mechanism
The mechanism underlying this phenomenon is not fully understood . However, the phenomenon of persistent luminescence must not be mistaken with fluorescenceFluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
and phosphorescence
Phosphorescence
Phosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum...
(see for definitions and ). Indeed, in fluorescence, the lifetime of the excited state is in the order of a few nanoseconds and in phosphorescence, even if the lifetime of the emission can reach several seconds, the reason of the long emission is due to the deexcitation between two electronic states of different spin multiplicity. For persistent luminescence, it has been known for a long time that the phenomenon involved energy traps (such as electron or hole trap) in a material which are filled during the excitation. After the end of the excitation, the stored energy is gradually released to emitter centers which emit light usually by a fluorescence-like mechanism.