Fluorescent
Solid substances that show luminescence are generally referred to as phosphor . Excitation with light , electron bombardment or other mechanisms generate light (in the context of fluorescent material in the visible range). The term phosphorus (plural) is derived from the English word phosphor for fluorescent material . The term luminescent “phosphor” is misleading, however, since luminescent materials do not contain any elemental phosphor . The correct name for phosphors is the word luminophore used in the Russian and French-speaking countries .
Basics
The luminous phenomena are based on fluorescence (immediate light emission with short-wave lighting), phosphorescence (time-delayed light emission after short-wave lighting) and cathodoluminescence (light emission when electron bombardment), sometimes electroluminescence in electrical fields.
Phosphors are often inorganic crystalline substances by selective introduction of impurities into the crystal structure provide a technically usable light output. This requires a purity of the raw materials of up to 99.9999%. The phosphors are mostly based on oxides or sulfides such as zinc oxide , zinc sulfide , zinc cadmium sulfide and zinc sulfide selenide as well as silicates such as willemite and zinc beryllium silicate. Zinc sulfide is also used in self-luminous radioactive luminous paints .
The doping element determines the luminous color, for example
- ZnS: Mn → orange-red
- ZnS: Ag → blue
- ZnS: Cu → green
- ZnS: Ln → red to blue-green depending on the lanthanoid
Important doping and basic elements are the lanthanoids europium (Eu), terbium (Tb) and cerium : Europium (III) -doped Y 2 O 2 S is used in color picture tubes as a red phosphor, Eu 3+ doped Y 2 O 3 is produced in Energy-saving lamps and other fluorescent gas discharge lamps show the red part of the spectrum. Terbium-doped gadolinium oxide sulfide Gd 2 O 2 S was used as a green phosphor in radar screens.
Cerium doped yttrium / gadolinium aluminum garnet powder is used in white light emitting diodes to convert blue light into yellow.
Parameters such as light color of fluorescence and phosphorescence, afterglow time and efficiency of energy reproduction are not only dependent on the substances used, but also on their processing such as annealing, grinding, quenching, and atmospheric influences during these processes.
Applications
- Screen coating of the cathode ray tube (CRT) in televisions, oscilloscopes, monitors (cathodoluminescence)
- Internal coating of fluorescent lamps and fluorescent tubes for the colors white and other colors (fluorescence)
- Coating of UV and blue LEDs to get white glowing LEDs.
- Daylight colors (safety clothing , highlighter ): these glow using (fluorescence) the blue component in daylight
- Security features on banknotes and securities through excited fluorescence.
- Safety signs and decorative objects that glow in the dark (phosphorescence with long afterglow period)
- Fluorescent markers for the investigation of biological processes by means of excitation by ultraviolet, for example with fluorescein
Other solid substances that emit light are generally not referred to as luminescent material, for the principles of light emission see under luminescence and luminous color .
literature
- Werner Espe: Materials science of high vacuum technology . 3: auxiliary materials. VEB Deutscher Verlag der Wissenschaften, Berlin 1961.
Web links
Individual evidence
- ↑ uni-freiburg.de: Chemistry of Metals, Chap. 7.1.
- ↑ Optimal phosphors for LED applications Thomas Jüstel Lecture at the 9th conference: LED in lighting technology, Essen 12.-13. March 2013. Retrieved December 24, 2017