What is the difference between Biofluorescence and Phosphorescence?

Biofluorescence is the absorption of light at one wavelength followed by its reemission at a lower energy and longer wavelength. It usually happens when molecules take in high-energy light, like Ultraviolet (UV) or blue light and then release some of that energy again as lower energy visible light. It appears to our eyes that fluorescent subjects and objects often seem to be actively glowing with an intense light under sunlight or a UV torch. They aren’t creating new energy, but rather they’re transforming invisible light into light that we can see. If we look at biofluorescence from a purely physical point of view, we can see that just like heat, sound or motion, it is one of the many ways living systems transform and release absorbed energy back into their surroundings.

Zooming in for a more detailed look at what’s going on we find that it all begins with an electron. When a photon, or particle of light, hits a fluorescent molecule it causes one of its electrons to become ‘excited’, or to jump up to a higher energy level. This excited state lasts only a tiny fraction of a second. The electron quickly falls back down to its normal position, and when it does it releases the excess energy as a new photon of light. During the process some of the energy is lost as heat or vibration which means the emitted light has less energy than the absorbed light. This is why the emitted light shifts from a shorter wavelength to a longer wavelength. It’s this re-emitted glow that we call fluorescence. Depending on the molecule, fluorescence can technically be excited by light of many different wavelengths. The reason it is normally triggered by short wavelengths is because they have a high enough amount of energy to excite the electrons and make the process possible. Longer, lower-energy wavelengths simply don’t have enough energy to excite most fluorescent molecules.