Fluorescence
Fluorescence
Fluorescence is a temporary physical phenomenon where the atoms of a substance get energized and excited by the incidence of high-energy electromagnetic radiation and emit light radiation in several transitions to lower energy states.When a fluorescent substance absorbs energy due to the incidence of X-ray, light waves, and electrons, it starts to emit visible light (longer wavelength) and slowly reaches the ground state from the partially excited state. This phenomenon is called fluorescence. The substances that show such activities are called fluorescent substances. As soon as the incident radiation is cut off, fluorescence ceases.
Chlorophyll is a good fluorescent substance occurring naturally in green plants. This pigment is used to trap sun rays and convert them into energy by initiating a biochemical reaction. The reaction stops when the sun rays cease to exist. This pigment only shows such behavior in the presence of a particular range of wavelengths.
Fluorescence has many practical applications, including mineralogy, gemology, medicine, chemical sensors (fluorescence spectroscopy), fluorescent labelling, dyes, biological detectors, cosmic-ray detection, vacuum fluorescent displays, and cathode-ray tubes. Its most common everyday application is in (gas-discharge) fluorescent lamps and LED lamps, in which fluorescent coatings convert UV or blue light into longer-wavelengths resulting in white light which can even appear indistinguishable from that of the traditional but energy- inefficient incandescent lamp.
Fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed.
Quantum Yield (Φ) = Number of photons emitted / Number of photons absorbed
The maximum possible fluorescence quantum yield is 1.0 (100%); each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent.
Fluorescence Quenching
Phosphorescence
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