Luminescence vs Phosphorescence
Light is a form of energy and to generate light another form of energy should be used. Production of light can occur in several mechanisms like below.
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.
Fluorescence is a type of luminescence too. 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. 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.
What is Phosphorescence?
When molecules absorb light and go to the excited state they have two options. They can either release energy and come back to the ground state immediately or can undergo other non-radiative processes. If the excited molecule undergoes a non radiative process, it emits some energy and come to a triplet state where the energy is somewhat lesser than the energy of the exited state, but it is higher than the ground state energy. Molecules can stay a bit longer in this less energy triplet state. This state is known as the metastable state. Then metastable state (triplet state) can slowly decay by emitting photons and can come back to the ground state (singlet state). When this happens, it is known as phosphorescence.
What is the difference between Luminescence and Phosphorescence?
• Luminescence is caused by various things like electric current, chemical reactions, nuclear radiation, electromagnetic radiation, etc. But phosphorescence takes place after a sample is irradiated with light.
• Phosphorescence remains for sometime even after the lighting source is removed. But luminescence is not so.
• Photoluminescence takes place when excited energy is released, and the molecule comes back to the ground state from the singlet-excited stage. Phosphorescence takes place when a molecule is coming back to the ground state form the triplet excited state (metastable state).
• The energy released in the luminescence process is higher than that in the phosphorescence.