Phosphors

Phosphors are materials that emit light when excited by energy such as ultraviolet light or electron beams. The emission results from radiative relaxation of excited states within the material. Most commonly, phosphors are inorganic crystalline hosts doped with luminescent activator ions. The host lattice provides a framework and transfers energy to dopant ions (for example Eu2+, Ce3+, Tb3+, Mn2+ in various hosts), which then emit light at characteristic wavelengths. Common host matrices include oxides and sulfides such as yttrium aluminum garnet (YAG), zinc sulfide (ZnS), and silicates; activators determine the emission color.

Phosphors are often categorized by their emission timing. Fluorescent phosphors emit light promptly during excitation, whereas phosphorescent or persistent phosphors store energy in defects or traps and release it after the excitation ceases, producing afterglow that can last from seconds to hours. The duration and color depend on the dopant, its concentration, and the host lattice. Persistent phosphors frequently rely on co-dopants to create traps (for example Dy3+ or other dopants) that store charge.

Synthesis methods include solid-state reactions, sol-gel processes, and hydrothermal growth to produce powders, single crystals, or thin films. Doping levels are optimized to balance absorption, energy transfer, and nonradiative losses, with goals of high quantum yield and photostability for display, lighting, and imaging applications.

Applications span lighting and displays (LED and CRT phosphors), scintillators in radiation detectors, X-ray screens, medical imaging, security inks, and various detector technologies. Research efforts focus on higher efficiency, broader color tunability, and improved thermal and chemical stability.