Spatial Distribution of the Distribution of the Electroluminescence and the Recombination Process in Tetracene Single Crystals

The spectral dependence of the recombination electroluminescence (REL) to photoluminescence (PH) ratio has been used as an experimental probe for studying the physical characteristics of the recombination in tetracene. A method is developed for determination of REL spatial distribution. In allcrystals studied, under conditions where two injecting contacts are used, the light emission is concentrated in front of the electrodes. At a sufficiently high voltage applied, a splitting up of the light emission zone in two layers is found in front of the anode. These experimental results can be explained qualitatively assuming appropriate gradients of charge densities, charge-quenching of the delayed component of the REL and charge densitydependence of the probability of a recombining electron-hole pair to yield a singlet exciton.