Electroluminescence in Pentacene Doped Anthracene Crystals

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The recombination radiation spectrum and its transient behavior were measured on a pentacene doped anthracene crystal. The recombination radiation spectrum was more sensitive to chemical or physical impurities than optically sensitized fluorescence spectrum. The intensity of both anthracene and pentacene emission was approximately proportional to the current. Anthracene or pentacene emission was found to consist of three components differing by their decay times; component 1 (decay time <10−5s), components 2,3 (decay times in the millisecond region, τ2<τ3). The component 1 was due to singlet excitons generated directly by carrier recombination. The component 2, the decay time of which was 2–3 ms, was due to triplet exciton annihilation, for its decay time was not affected by a reverse bias voltage and was equal to one half of the observed phosphorescence lifetime. The component 3, which was removed by a reverse bias voltage, was due to detrapped-trapped carrier recombination. Pentacene chemical impurity works as carrier traps or tirplet exciton traps. Anthracene lattice defects work as carrier traps. The SCLC measurement showed the existence of an electron discrete trap introduced by pentacene and electron and hole exponential traps. The present experimental results showed het importance of traps in the recombination process in a mixed crystal.
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