Becquerel, Antoine Henri (1852-1908), French physicist and Nobel laureate, who discovered radioactivity in uranium. He was the son of Alexandre Becquerel, who studied light and phosphorescence and invented the phosphoroscope, and grandson of Antoine César Becquerel, one of the founders of electrochemistry.
Born in Paris, Becquerel became professor of physics at the Museum of Natural History in 1892 and at the Polytechnical School in 1895. In 1896 he accidentally discovered the phenomenon of radioactivity in the course of his research on fluorescence. After placing uranium salts on a photographic plate in a dark area, Becquerel found that the plate had become blackened. This proved that uranium must give off its own energy, which later became known as radiation.
Becquerel also conducted important research on phosphorescence, spectrum analysis, and the absorption of light. In 1903 Becquerel shared the Nobel Prize in physics with the French physicists Pierre Curie and Marie Curie for their work on radioactivity, a term Marie Curie coined. His works include Recherches sur la phosphorescence (Research on Phosphorescence, 1882-1897) and Decouverte des radiations invisibles émises par l'uranium (Discovery of the Invisible Radiation Emitted by Uranium, 1896-1897).


Luminescence, emission of light by means other than combustion and therefore occurring at lower temperatures than are required for combustion. Examples of luminescence are the light, or glow, emitted by a luminous watch dial. Luminescence contrasts with incandescence, which is the production of light by heated materials.
When certain materials absorb various kinds of energy, some of the energy may be emitted as light. This process involves two steps: (1) the incidental energy causes the electrons of the atoms of the absorbing material to become excited and jump from the inner orbits of the atoms to the outer orbits; (2) when the electrons fall back to their original state, a photon of light is emitted. The interval between the two steps may be short (less than 1/100,000 of a sec) or long (many hours). If the interval is short, the process is called fluorescence; if the interval is long, the process is called phosphorescence. In either case the light produced is almost always of lesser energy, that is, of longer wavelength, than the exciting light. Fluorescence and phosphorescence have a number of practical applications.