= Phosphorescence
<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.
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