Enhancement of electroluminescence utilizing confined energy transfer for red light emission

Organic light emitting diodes (OLED) have been attracting attention because of their advantages in emission in a wide visible region and for applications to flat-panels or as light sources for optical signal circuits or other applications. In this paper, we report the fabrication and emission characteristics of two kinds of electroluminescence devices for enhanced red light emission utilizing energy transfer and energy confinement. The device consists of two materials systems: one is a co-doped OLED which consists of two different kinds of dye materials doped in an emissive layer, and the other type is a europium (Eu) complex doped in poly(N-vinylcarbazole), which are discussed. The results show that, in both cases, the enhancement of emission can be observed by the energy confinement of carriers. The mechanism of enhancement of emission is discussed, in terms of carrier confinement and by utilizing an energy band diagram of the emissive materials. (C) 2001 Elsevier Science B.V. All rights reserved.