Electroluminescence
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Electroluminescence (EL) is an
Mechanism
Electroluminescence is the result of
It has been recently shown that as a solar cell improves its light-to-electricity efficiency (improved open-circuit voltage), it will also improve its electricity-to-light (EL) efficiency.[1]
Characteristics
Electroluminescent technologies have low power consumption compared to competing lighting technologies, such as neon or fluorescent lamps. This, together with the thinness of the material, has made EL technology valuable to the advertising industry. Relevant advertising applications include electroluminescent billboards and signs. EL manufacturers can control precisely which areas of an electroluminescent sheet illuminate, and when. This has given advertisers the ability to create more dynamic advertising that is still compatible with traditional advertising spaces.
An EL film is a so-called Lambertian radiator: unlike with neon lamps, filament lamps, or LEDs, the brightness of the surface appears the same from all angles of view; electroluminescent light is not directional. The light emitted from the surface is perfectly homogeneous and is well-perceived by the eye. EL film produces single-frequency (monochromatic) light that has a very narrow bandwidth, is uniform and visible from a great distance.
In principle, EL lamps can be made in any color. However, the commonly used greenish color closely matches the peak sensitivity of human vision, producing the greatest apparent light output for the least electrical power input. Unlike neon and fluorescent lamps, EL lamps are not negative resistance devices so no extra circuitry is needed to regulate the amount of current flowing through them. A new technology now being used is based on multispectral phosphors that emit light from 600 to 400 nm depending on the drive frequency; this is similar to the color-changing effect seen with aqua EL sheet but on a larger scale.
Examples of electroluminescent materials
Electroluminescent devices are fabricated using either organic or inorganic electroluminescent materials. The active materials are generally semiconductors of wide enough bandwidth to allow the exit of the light.
The most typical inorganic thin-film EL (TFEL) is ZnS:Mn with yellow-orange emission. Examples of the range of EL material include:
- Powdered zinc sulfide doped with copper (producing greenish light) or silver (producing bright blue light)
- Thin-film zinc sulfide doped with manganese (producing orange-red color)
- Naturally blue diamond, which includes a trace of boron that acts as a dopant.
- Semiconductors containing Group III and Group V elements, such as indium phosphide (InP), gallium arsenide (GaAs), and gallium nitride (GaN) (Light-emitting diodes.)
- Certain organic semiconductors, such as [Ru(bpy)3]2+(PF6−)2, where bpy is 2,2'-bipyridine
Practical implementations
The most common electroluminescent (EL) devices are composed of either powder (primarily used in lighting applications) or thin films (for information displays.)
Light-emitting capacitor (LEC)
Light-emitting capacitor, or LEC, is a term used since at least 1961
Electroluminescent automotive instrument panel backlighting, with each gauge pointer also an individual light source, entered production on 1960 Chrysler and Imperial passenger cars, and was continued successfully on several Chrysler vehicles through 1967 and marketed as "Panelescent Lighting".
Night lights
The Sylvania Lighting Division in Salem and Danvers, Massachusetts, produced and marketed an EL night light, under the trade name Panelescent at roughly the same time that the Chrysler instrument panels entered production. These lamps have proven extremely reliable, with some samples known to be still functional after nearly 50 years of continuous operation.[when?]
Later in the 1960s, Sylvania's Electronic Systems Division in
Display backlighting
Powder phosphor-based electroluminescent panels are frequently used as backlights for
EL backlights require relatively high voltage (between 60 and 600 volts).[4] For battery-operated devices, this voltage must be generated by a boost converter circuit within the device. This converter often makes a faintly audible whine or siren sound while the backlight is activated. Line-voltage-operated devices may be activated directly from the power line; some electroluminescent nightlights operate in this fashion. Brightness per unit area increases with increased voltage and frequency.[4]
Thin-film phosphor electroluminescence was first commercialized during the 1980s by Sharp Corporation in Japan, Finlux (Oy Lohja Ab) in Finland, and Planar Systems in the US. In these devices, bright, long-life light emission is achieved in thin-film yellow-emitting manganese-doped zinc sulfide material. Displays using this technology were manufactured for medical and vehicle applications where ruggedness and wide viewing angles were crucial, and liquid crystal displays were not well developed. In 1992, Timex introduced its Indiglo EL display on some watches.
Recently,[when?] blue-, red-, and green-emitting thin film electroluminescent materials that offer the potential for long life and full-color electroluminescent displays have been developed.
The EL material must be enclosed between two electrodes and at least one electrode must be transparent to allow the escape of the produced light. Glass coated with
The display applications are primarily passive (i.e., voltages are driven from the edge of the display cf. driven from a transistor on the display). Similar to LCD trends, there have also been Active Matrix EL (AMEL) displays demonstrated, where the circuitry is added to prolong voltages at each pixel. The solid-state nature of TFEL allows for a very rugged and high-resolution display fabricated even on silicon substrates. AMEL displays of 1280×1024 at over 1000 lines per inch (LPI) have been demonstrated by a consortium including Planar Systems.[5][6]
Thick-film dielectric electroluminescent technology
Thick-film dielectric electroluminescent technology (TDEL) is a
Color By Blue
Color By Blue (CBB) was developed in 2003.[8] The Color By Blue process achieves higher luminance and better performance than the previous triple pattern process, with increased contrast, grayscale rendition, and color uniformity across the panel. Color By Blue is based on the physics of photoluminescence. High luminance inorganic blue phosphor is used in combination with specialized color conversion materials, which absorb the blue light and re-emit red or green light, to generate the other colors.
New applications
Electroluminescent lighting is now used as an application for public safety identification involving alphanumeric characters on the roof of vehicles for clear visibility from an aerial perspective.[9]
Electroluminescent lighting, especially electroluminescent wire (EL wire), has also made its way into clothing as many designers have brought this technology to the entertainment and nightlife industry.[10] From 2006, t-shirts with an electroluminescent panel stylized as an audio equalizer, the T-Qualizer, saw a brief period of popularity.[11]
Engineers have developed an electroluminescent "skin" that can stretch more than six times its original size while still emitting light. This hyper-elastic light-emitting capacitor (HLEC) can endure more than twice the strain of previously tested stretchable displays. It consists of layers of transparent hydrogel electrodes sandwiching an insulating elastomer sheet. The elastomer changes luminance and capacitance when stretched, rolled, and otherwise deformed. In addition to its ability to emit light under a strain of greater than 480% of its original size, the group's HLEC was shown to be capable of being integrated into a soft robotic system. Three six-layer HLEC panels were bound together to form a crawling soft robot, with the top four layers making up the light-up skin and the bottom two the pneumatic actuators. The discovery could lead to significant advances in health care, transportation, electronic communication and other areas.[12]
See also
References
- .
- ^ Proceedings of the National Electronics Conference, Volume 17, National Engineering Conference, Inc., 1961; page 328
- ISBN 0881733784, pages 122–124
- ^ ISBN 0-07-020974-Xpp 22-28
- ^ Ron Khormaei, et al., "High-Resolution Active Matrix Electroluminescent Display", Society for Information Display Digest, p. 137, 1994.
- ^ "Active Matrix Electroluminescence (AMEL)" (PDF). Archived from the original (PDF) on 2012-07-22.
- ^ Akkad, Omar El (17 March 2006). "The next big (flat) thing". The Globe and Mail.
- ^ "iFire: Sparking a New Revolution in Flat Panel Technology". www.ifire.com.
- ^ "air-el". Federal Signal. Retrieved July 23, 2016.
- ^ Diana Eng. "Fashion Geek: Clothes Accessories Tech". 2009.
- ^ Jain, Bupesh. "T-Qualizer: The beat goes on". CNET. Retrieved 2022-12-08.
- ^ Cornell University (March 3, 2016). "Super elastic electroluminescent 'skin' will soon create mood robots". Science Daily. Retrieved March 4, 2016.
External links
- Overview of electroluminescent display technology, and thediscovery of electroluminescence Archived 2012-04-30 at the Wayback Machine
- Chrysler Corporation press release introducing Panelescent (EL) Lighting on Archived 2006-11-12 at the Wayback Machine
- 8 September, 1959. Archived 2006-11-12 at the Wayback Machine