Difference Between Fluorescence and Luminescence

Fluorescence vs Luminescence
 

Luminescence is a process of emitting light. This can occur by various means. In this article, we will discuss those methods and types of light emitting process.

What is Fluorescence?

Electrons in an atom or a molecule can absorb the energy in the electromagnetic radiation and thereby excite to an upper energy state. This upper energy state is unstable; therefore, electron likes to come back to the ground state. When coming back, it emits the absorbed wavelength. In this relaxation process, they emit excess energy as photons. This relaxation process is known as fluorescence. Fluorescence takes place much more rapidly and generally complete in about 10-5 s or less time from the time of excitation. In atomic fluorescence, gaseous atoms fluoresce when they are exposed to radiation with a wavelength that exactly matches one of the absorption lines of the element. For example, gaseous sodium atoms absorb and excite by absorbing 589 nm radiations. Relaxation takes place after this by reemission of fluorescent radiation of the identical wavelength. Because of this, we can use fluorescence to identify different elements. When excitation and reemission wavelengths are the same, the resulting emission is called resonance fluorescence. Other than fluorescence, there are other mechanisms by which an excited atom or molecule can give up its excess energy and relax to its ground state. Nonradiative relaxation and fluorescence emissions are two such important mechanisms. Because of many mechanisms, the lifetime of an excited state is brief. The relative number of molecules that fluoresce is small because fluorescence requires structural features that slow the rate of the nonradiative relaxation and enhance the rate of fluorescence. In most molecules, these features are not there; therefore, they undergo nonradiative relaxation, and fluorescence does not occur. Molecular fluorescence bands are made up of a large number of closely spaced lines; therefore, usually it is hard to resolve.

What is Luminescence?

Luminescence is the process of emitting light from a substance. This emission is not due to heat; therefore, it is a form of cold body radiation. There are few types of luminescence as bioluminescence, chemiluminescence, electrochemiluminescence, electroluminescence, photoluminescence, etc. Bioluminescence is the emission of light by living organisms. For example, fireflies can be considered. This is a natural process. Light is released as a result of a chemical reaction taking place inside the organism. In fireflies, when the chemical called luciferin reacts with oxygen, the light is produced. This reaction is catalyzed by the enzyme luciferase. Chemiluminescence is a result of a chemical reaction. In fact, bioluminescence is a type of chemiluminescence. For example, the catalyzed reaction between luminal and hydrogen peroxide produces light. Electrochemiluminescence is a type of luminescence produced during an electrochemical reaction.