Fluorescence and phosphorescence

  • When an electron absorbs a high energy photon, excitation can occur across several energy levels
  • On de-excitation, the atomic electron makes several smaller steps back to ground state
  • Hence, these steps result in the emissions of photons, which are visible

fluorescence and phosphorescence

E.g. UV light, which is invisible, can be used to view stains such as blood.

  • The light excites the electrons in the blood, causing them to increase energy levels
  • When de-excite, they do so in discrete steps.
  • Hence, the photons they emit are of lower energy/frequency and hence visible

When this occurs fast, it is called fluorescence

When it occurs over a long period of time, it is called phosphorescence

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