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Posted: Nov 06, 2017
Brighter flexible electroluminescent film by adopting eye structure of nocturnal animals
(Nanowerk News) A research team of DGIST's Intelligent Devices and Systems Research Group has developed an electroluminescent film that is four times brighter than the existing one. The research team led by Dr. Byeong-dae Choi has developed a technology which can improve the luminance of electroluminescent devices by 422% compared to the conventional ones by applying retro-reflection electrodes that adapt the principle of nocturnal animal eyes (Advanced Materials Technologies, "Highly Bright Flexible Electroluminescent Devices with Retroreflective Electrodes").
Electroluminescent (EL) refers to an optical and electrical phenomenon in which a material emits light in response to the passage of an electric current. Electroluminescent films using the phosphor powder have advantages such as excellent durability in a deformed state due to flexibility and elasticity, and high efficiency despite low cost. However, it was difficult to put into practical use due to their low brightness.
This is a structure and characteristics of electroluminescent device using recursive reflection structure. Structures (a~e) and viewing angle characteristics (f) of an electroluminescent device using a retroreflective structure. It exhibits a wide light reflection characteristic (Reflected EL) of -60° and 60° when viewing angle characteristics are evaluate. (Image: DGIST) (click on image to enlarge)
In order to increase the brightness of electroluminescent devices, the research team paid attention to the eyes of nocturnal animals with high utilization efficiency of light. The researchers used the retro-reflection characteristics that the light returns to the light source without being dispersed in the retroreflective structure of the nocturnal animal eye while it is scattered in the normal reflection structure.
The researchers fabricated an electroluminescent film coated with a light-transmitting luminescent film on a retroreflective electrode and have found that a light source composed of phosphor particles of several micrometers (µm) in size can have a wide viewing angle of reflected light on the prismatic retroreflective electrode surface.
In addition, the team has discovered that when the light source has a transmittance higher than a certain value, there is no loss of reflected light and it enables to fabricate high luminance electroluminescent light source by controlling the concentration of luminescent particles. The team also developed a film that improved brightness by 442% (1017cd/m-2, 6.67V/µm-1 at 10kHz) compared to conventional technology by blending luminescent particle-polymer binder complexes at specific ratios.
Unlike conventional electroluminescent lights, that are made of glass or plastic and used for lighting or light source for advertisement, highly bright electroluminescent film is flexible and bendable. Moreover, it is expected to replace the existing electroluminescent lighting as it is able to be produced at room temperature.
Dr. Byeongdae Choi stated "This study is significant as it has applied the light reflection principle of nocturnal animal eyes, which have high light utilization efficiency, to light emitting devices." He added "Since this technology can also be applied to self-luminous displays, it is expected to contribute to strengthening Korea's competitiveness in the global lighting market, which is estimated to reach more than 120 trillion won per year in the future, as well as the next generation display market."
Source: DGIST (Daegu Gyeongbuk Institute of Science and Technology)