Triplet exciton fusion and singlet excition fission have been observed in tetracene crystals, and the magnetic field dependence and the rate constants for these processes have been measured. At 0°C the singlet fission rate constant and the triplet-triplet fusion rate constant (leading to excited singlets) are (6.3±0.7) ×${10}^8$ ${\sec }^{-1\mathrm{}}$ and 9×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^3$ sec-1 (within an order of magnitude), respectively.

• Received 1 July 1969

DOI:https://doi.org/10.1103/PhysRevB.1.815