Stokes Shift
Instrumental Project: Finding the Stokes Shift
The Stokes shift is a phenomenon that occurs in fluorescence, where the absorbed photons have a higher energy than the emitted photons. This results in a shift in the wavelength of the emitted light towards longer wavelengths (i.e. towards the red end of the spectrum). In fluorescence, a molecule absorbs a photon of light and becomes excited to a higher energy state. This excited state is unstable, and the molecule will quickly relax back to its ground state by emitting a photon of light. Because the energy of the emitted photon is lower than the absorbed photon, the light is shifted towards longer wavelengths. This shift is illustrated in the image above. The magnitude of the Stokes shift depends on the specific molecules involved, but it is typically on the order of tens to hundreds of nanometers
UV/Vis Spectroscopy
Ultraviolet-visible spectroscopy is an analytical technique used to gather the absorbance spectra of a sample. These photons of light excite electrons from the ground state to the first singlet excited state, this is the energy absorbed. This then can become a measurement of how much light the sample has absorbed as opposed to how much light was able to pass through the sample.
Fluorimetry
Fluorescence is simply the light that molecules give off when they've been excited or when they've gone to an excited electronic state. Molecules don't stay in these excited states very long, they will lose their energy to return to the ground state. There are various ways to do this. One way way is through the emission of photons.