ultraviolet light emitting diode (UV-LED)
UV light-emitting diodes(UV- LED) emit ultraviolet light. According to DIN 5031, the UV range is divided into the wavelength ranges UV-A with wavelengths between 315 nm and 380 nm, UV-B between 280 nm and 315 nm, and UV-C with wavelengths between 100 nm and 280 nm. UV LEDs are available for wavelengths between about 380 nm and 240 nm.
The efficiency of UV LEDs decreases rapidly with shorter wavelengths and is 2 % to 3 % at wavelengths below 280 nm. The achievable UV outputs are correspondingly low, namely a few milliwatts.
Like conventional light-emitting diodes, UV LEDs use gallium nitride( GaN) as a base material, which is enriched by other metals, but also aluminum nitride ( AIN) and aluminum gallium nitride (AlGaN). The enrichment can shift the emission wavelengths. UV LEDs have a much shorter lifetime compared to normal light emitting diodes and a much lower efficiency, which is especially low for UV-C LEDs at wavelengths between 200 nm and 280 nm. These wavelengths are not perceptible by humans. They are used for killing viruses, bacteria and other germs. The low efficiency has physical, optical and also material reasons, which show up in crystalline defects. The optical problems show up in the radiation decoupling.
UV-LEDs are also used for the production of white light emitting diodes, the White LED(WLED). For this purpose, the UV LED is equipped with an RGB converter, which emits the UV light in the primary colorsred, green, blue (RGB). The color emission of each color is more broadband, resulting in a higher color rendering index. However, the conversion of the UV light into the individual colors involves a loss of energy, which is dissipated as heat.
UV LEDs in the form of UV lamps are used in surface treatment, in medical laboratories for the disinfection and sterilization of water and air treatment, as well as for checking banknotes and curing adhesives.