Previous observations of delayed fluorescence quenching by carricrs in anthracene crystals are reanalyzed. It had been observed that this quenching was caused by two different mechanisms, namely the well-known triplet annihilation by carriers together with a hitherto unobserved annihilation process that is linear in the carrier concentration but quadratic in the concentration of triplet excitons. Two kinetic models for the latter process are considered and compared : (i) annihilation of triplet pairs by carriers and (ii) triplet-carrier interaction leading to quartet-excited carriers which are assumed to interact more strongly than unexcited carriers with triplet excitons. Triplet pairs have been observed in magnetic field experiments but their lifetime is much too short to explain the observed quenching. Quartet states are expected to have the required long lifetime, since their decay is spinforbidden, although no independent evidence for their participation has been obtained so far.
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Slchwob et al. (1973) studied this question.
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