phosphor

Phosphor, from the Greek phos "light" and phoros "bearing," refers to two related concepts: a chemical element and luminescent materials that emit light when excited.

Phosphorus is a non-metal in group 15 (the pnictogens) with the symbol P and atomic number 15. It occurs in white, red, and black allotropes. White phosphorus is a waxy, highly reactive substance that ignites in air and must be stored under water; red phosphorus is more stable; black phosphorus is the most thermodynamically stable allotrope. Phosphorus is ubiquitous in minerals as phosphate and is essential for life, participating in energy transfer, nucleic acids, and cell membranes.

Most often, the term "phosphor" refers to luminescent materials that absorb energy and re-emit it as light. Phosphors are used in fluorescent lamps, cathode-ray tubes, light-emitting diodes, and glow-in-the-dark products. They are typically inorganic compounds doped with activator ions to tailor color and persistence. Common systems include europium-doped strontium aluminate, known for long afterglow; cerium-doped yttrium aluminum garnet, used in white LEDs; and zinc sulfide activated with silver, found in earlier display technologies.

Industrially, phosphorus compounds are produced from phosphate rock, typically via high-temperature reduction, and are used to manufacture fertilizers, phosphoric acids, and various chemicals. Phosphorus also forms compounds involved in flame retardants and detergents, though environmental and health concerns have influenced some applications.

Safety and storage considerations center on white phosphorus, which is toxic and highly reactive; it is stored under water to prevent spontaneous ignition and oxidation.