Singlet-Triplet Interactions in Crystalline Anthracene

A new carrier-generation mechanism is observed in anthracene and is attributed to singlet-triplet annihilation. The rate constant for ionization following this annihilation is estimated to be ${\alpha }_{\mathrm{ST}}\simeq {10}^{-12\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$. The experiments give also a new value for the singlet-singlet annihilation rate constant, ${\alpha }_{\mathrm{SS}}\simeq {2.10}^{-11\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$. The possibility of other interpretations of the data is discussed.