Phosphorescence
A type of photoluminescence where absorbed energy is emitted slowly over time due to spin-forbidden quantum transitions.
Governing formula
τ_phosphorescence ~ 10⁻³ s to hours
SI unit
Seconds to Hours (Lifetime)
In depth
Excited electrons undergo intersystem crossing into a triplet state (T₁). Decaying back to the singlet ground state (S₀) is spin-forbidden by selection rules, trapping electrons so emission leaks out slowly over minutes or hours.
Examples in the real world
Glow-in-the-dark watch dials, emergency exit signs, and safety stickers glowing after dark.