Stokes shift

Stokes shift is a phenomenon that occurs when light is emitted from some atoms or molecules. It happens because the light particles (called photons) get energy when they are released, and this energy is different from the energy that the atoms or molecules had before the light was released. Technically, the energy of the light particles is higher than the energy of the atoms or molecules that released them! So, when the light is emitted, the energy of the light particles is a bit higher then the energy of the atoms or molecules. That difference in energy is called a Stokes shift.