A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness (>1ms), and fluorescent materials, where the emission decay takes place over tens of nanoseconds. Phosphorescent materials are known for their use in radar screens and glow-in-the-dark toys, whereas fluorescent materials are common in CRT and plasma video display screens, sensors, and white LEDs.
Phosphors are often transition metal compounds or rare earth compounds of various types. The most common uses of phosphors are in CRT displays and fluorescent lights. CRT phosphors were standardized beginning around World War II and designated by the letter "P" followed by a number.
Phosphorus, the chemical element named for its light-emitting behavior, emits light due to chemiluminescence, not phosphorescence.
An aperture grille (tension mask) is one of two major technologies used to manufacture color cathode ray tube (CRT) televisions and computer displays; the other is shadow mask.
Fine vertical wires behind the front glass of the display screen separate the different colors of phosphors into strips. These wires are positioned such that an electron beam from one of three guns at the rear of the tube is only able to strike phosphors of the appropriate color. That is, the blue electron gun will strike blue phosphors, but will find a wire blocks the path to red and green phosphors.
The fine wires allow for a finer dot pitch as they can be spaced much closer together than the perforations of a shadow mask, and there need be no gap between adjacent horizontal pixels.
During the display of bright images, a shadow mask warms, and expand outward in all directions (sometimes called blooming). Aperture grilles do not exhibit this behavior; when the wires heat up, they expand vertically. Because there are no defined holes, this expansion does not affect the image, and the wires do not move horizontally.
The vertical wires of the aperture grille have a resonant frequency and will vibrate in sympathetic resonance with loud sounds near the display, resulting in fluttering and shimmering of colors on the display. To reduce these resonant effects, one or two horizontal stabilizing wires, called "damping wires", are welded across the grille wires, and may be visible as fine dark lines across the face of the screen. These stabilizing wires provide the easiest way to distinguish aperture grille and shadow mask displays at a glance. The stabilized grille can still vibrate but the sounds need to be loud and close to the display.