Techniques {phosphorescence}| can use absorbed-light re-emission. Orbital ground state is singlet with spins paired. Lower excited orbital state is triplet with spins parallel. Higher excited orbital state is singlet with spins paired. Electron can fall from excited singlet to triplet if heavy atom is available to change angular momentum. Electron can fall from triplet to singlet ground state if heavy atom is available to change angular momentum. Electron fall requires heavy-atom collision. In gas, process is fast. In liquids, process is moderate. In solids, process is slow, so phosphorescence lasts several seconds. Electron-gun TV screens and fluorescent lights have phosphor coatings.
fluorescence
Fluorescence uses ultraviolet light to put electrons in high orbitals, from which they fall back to lower excited orbitals, by short vibration-induced jumps, from which they fall to lowest band by spontaneous emission, giving visible light. Fluorescence does not require collisions because momentum does not change, so fluorescence is fast.
Physical Sciences>Chemistry>Analytical Chemistry>Light Intensity
5-Chemistry-Analytical Chemistry-Light Intensity
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Date Modified: 2022.0224