Phosphorescence is delayed luminescence sustained by long-lived excited states after excitation has ceased. In a common molecular mechanism, population reaches a triplet state and returns to a singlet ground state through a weak, spin-changing transition. Long-lived emission in a solid can also involve trapped charge carriers, so a slow decay alone does not uniquely establish the microscopic mechanism.
A useful experiment shutters the excitation and records emitted intensity versus time with a photodetector. Scattered excitation should disappear with the shutter, whereas delayed emission persists. The measured decay can depend on temperature, quenching and multiple states rather than following one universal lifetime.
Phosphorescence is a type of photoluminescence related to fluorescence. It occurs when a material absorbs light or electromagnetic radiation and then re-emits it over a longer period. Unlike fluorescence, which involves the immediate re-emission of light (typically within nanoseconds), phosphorescence involves a delayed re-emission that can last from microseconds to several hours or even days.
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