Eiji Shikoh, an assistant professor at the Japan Advanced Institute of Science and Technology, developed an OLED device that emits circularly polarized light in the visible light range.
It is a basic technology to enable 3D representation on OLED and electronic paper displays. To produce the circularly polarized light in the visible light range, the spin state during the light emission process is controlled by injecting a spin-polarized carrier from the ferromagnetic negative electrode into the emission layer.
For the future, Shikoh intends to increase the degree of circular polarization so that two components, the right and left circularly polarized light, may be clearly differentiated. Through this method, he aims to realize 3D display by producing parallax images that have different information in each component.
In general, OLED devices use a nonmagnetic material such as aluminum (Al) for their negative electrodes. But the new technology uses a ferromagnetic material such as iron (Fe) for the negative electrode in order to inject spin-polarized electrons from the ferromagnetic negative electrode into the emission layer.
As a result, light emission with a circular polarization degree of about 0.5% was observed when a magnetic field intensity of 3,000Oe is applied at room temperature, Shikoh said.
It has been known that GaAs-based inorganic LEDs produce circularly polarized light by the spin injection into the emission layer. However, those LEDs cannot be used for displays, etc because they emit light in the infrared range. Moreover, the base material has to be changed in order to precisely control the colors of light emitted by inorganic light emitting devices.
With organic molecules, it is possible to precisely control the emission color by changing the functional group, Shikoh said.
The research was conducted as part of the Industrial Technology Research Grant Program promoted by Japan's New Energy and Industrial Technology Development Organization (NEDO).