Luminescence is the emission of light from a cool object, in contrast to incandescence which is the emission of light from a hot object. There are three main types of luminescence: phosphorescence involves the absorption and slow re-emission of light, fluorescence involves fast absorption and re-emission of light, and chemiluminescence is the emission of light driven by a chemical reaction. Phosphorescent minerals will glow after exposure to UV light. Fluorescence is seen in scorpion exoskeletons and deep sea organisms. Chemiluminescence, the most common form in living organisms, is used by fireflies, deep sea fish, and microorganisms.

1. MOHAMMAD IMRAN AZIZ Assistant Professor PHYSICS DEPARTMENT SHIBLI NATIONAL COLLEGE, AZAMGARH(India). Introduction to Luminescence

2. What is luminescence? Luminescence is a general term for the emission of light from a cool object. (In contrast to, e.g., incandescence – the emission of light from a hot piece of metals such as the filament in a light bulb.) There are many examples of naturally occurring luminescence. Most of these fall into one of 3 categories: Phosphorescence : Absorption and slow re-emission of light. Most commonly observed in minerals. Fluorescence : Absorption and fast re-emission of light. Seen in deep sea organisms and some insects and plants. Chemiluminescence : Emission of light driven by a chemical reaction. The most common form of natural luminescence (often called “bioluminescence”). Seen in aquatic organisms, insects and plants.

3. Phosphorescence Certain minerals will glow in the dark when exposed to ultraviolet (UV) light. Some of them continue to glow even after the ultraviolet light is turned off. This “slow” re-emission of light is known as phosphorescence. The first phosphorescent mineral was reported in the early 1600s. These minerals, or “inorganic phosphors” have many interesting uses – for example, they are used in making the cathode ray tubes still used in older color televisions.

4. Fluorescence Like phosphorescence, fluorescence involves absorbing and re-emitting light. However, fluorescence is very fast, and is disappears as soon as there is no more light to absorb. While some minerals are reported to fluoresce, this is usually phosphorescence that has been given the wrong name. An interesting example of natural fluorescence is the exoskeleton of scorpions – scorpions glow under UV light! People are still arguing about whether this fluorescence has a biological role, or if it is just a coincidence. For people who like to collect scorpions, it makes them easy to find at night with a portable UV lamp.

5. Chemiluminescence Chemiluminescence is the generation of light by a chemical reaction. This is the most common form of luminescence in living organisms. Insects like fireflies use chemiluminescence to attract their mates, deep sea fish like the Anglerfish use it to lure prey close to their mouth and microorganisms use it to signal distress. Recent studies suggest that humans may give off light too, although this is controversial.