A quasistable electron excitation state involving a change of spin state (intersystem crossing) which decays only slowly. In phosphorescence, light emitted by an atom or molecule that persists after the exciting source is removed. It is similar to fluorescence, but the species is excited to a metastable state from which a transition to the initial state is forbidden. Emission occurs when thermal energy raises the electron to a state from which it can de-excite. Therefore, phosphorescence is temperature-dependent.
