Stokes Shift - Stokes Fluorescence

Stokes Fluorescence

Stokes fluorescence is the re-emission of longer wavelength photons (lower frequency or energy) by a molecule that has absorbed photons of shorter wavelengths (higher frequency or energy). Both absorption and radiation (emission) of energy are unique characteristics of a particular molecular structure. If a material has a direct bandgap in the range of visible light, the light shining on it is absorbed, causing electrons to become excited to a higher energy state. The electrons remain in the excited state for about 10−8 seconds. This number varies over several orders of magnitude depending on the sample, and is known as the fluorescence lifetime of the sample. After losing a small amount of energy in some way (hence the longer wavelength), the electron returns to the ground state and energy is emitted.