Topic overview

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Radiative decay releases energy as a photon: fluorescence generally involves an S₁ → S₀ transition, while phosphorescence involves a T₁ → S₀ transition after intersystem crossing. Their different spin selection rules are reflected in their emission behavior and lifetimes. Non-radiative pathways release energy without photon emission or transfer it to another molecule; examples include vibrational relaxation, internal conversion, and intersystem crossing. Quantum yield expresses the balance between emitted and absorbed photons, shaped by competition between radiative and non-radiative rates. Ideas such as Kasha’s rule, the Stokes shift, and the Franck–Condon principle help interpret transitions and spectra. A Jablonski diagram provides a visual framework for comparing these pathways.