A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam in a cathode-ray tube.
Example of phosphorescence
Monochrome monitor
Aperture grille CRT phosphors
Luminescence is the "spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment". A luminescent object is emitting "cold light", in contrast to "incandescence", where an object only emits light after heating. Generally, the emission of light is due to the movement of electrons between different energy levels within an atom after excitation by external factors. However, the exact mechanism of light emission in vibrationally excited species is unknown.
Luminol and haemoglobin, an example of chemiluminescence
UV-photoluminescence in microbiological diagnostics