A research team from 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 percent, compared to the conventional ones, by applying retro-reflection electrodes that adapt the principle of nocturnal animal eyes.
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 phosphor powder have advantages like excellent durability in a deformed state due to flexibility, elasticity and high efficiency, even though they are low cost. But it was difficult to put into practical use due to their low brightness.
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 runs 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 in 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.
The team also discovered that when the light source has a transmittance higher than a certain value, there is no loss of reflected light. It enables it 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 percent compared to conventional technology by blending luminescent particle-polymer binder complexes at specific ratios.
Unlike conventional electroluminescent lights, which are made of glass or plastic and typically used for lighting or light source for advertisement, the highly bright electroluminescent film is flexible and bendable. Moreover, it is expected to replace the existing electroluminescent lighting as it is able to produce at room temperature.
"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," Dr. Byeongdae Choi said. "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."
A paper on this research was published in Advanced Materials.