SPIN EFFECTS ON THE LUMINESCENCE YIELD OF ORGANIC LIGHT-EMITTING-DIODES

The influence of the excitation spectrum on the quantum yield is inves tigated for organic molecules used in Light emitting diodes (LEDs). Th e significance of the competition between radiative and nonradiative r ecombination channels is pointed out. A system of master equations is proposed to describe the relaxation of lower levels of the excited mol ecule, and the solution for the fluorescence yield is obtained assumin g relatively weak vibronic coupling. The results are used to interpret the experimental data in oligothiophenes, and general approaches are proposed to increase the relative weight of the radiative decay channe l and correspondingly enhance the working properties of organic Light emitting diodes. In particular, the fluorescence quantum yield tan exc eed the simple estimate of 0.25. (C) 1998 American Institute of Physic s.