SACE Stage 2 Physics — Light & Atoms 3.3

Fluorescence & Phosphorescence

A UV photon excites a molecule to a high-energy state. In fluorescence the molecule emits a visible photon almost instantly; in phosphorescence it gets trapped in a metastable state (T₁) first, then emits later at even lower energy. One high-energy photon in; one lower-energy visible photon out — after a delay that can last seconds.