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
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