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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
Fluorescence is different from phosphorescence, in that in case of fluorescence the absorbed light radiation is re-emitted instantaneously in one or more steps and ceases with removal of light source, while in the case of phosphorescence the absorbed light is still given out slowly, long after the removal of source light.
Fluorescence is a particular form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region, which gives the fluorescent substance a distinct color that can be seen only when exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.
Fluorescence can be made stronger by chemical reaction or by lowering the temperature.
Materials known for fluorescence
- Ethacridine lactate (Rivanol)
- Peanut butter
- Quinine (like in tonic water)
- Riboflavin (Vitamin B2)
- Security signs on most banknotes