Ruby‐Laser‐Excited Delayed Fluorescence of Crystalline Tetracene. Combined Effects of Trap Saturation and Bimolecular Processes

The temporal decay of ruby‐laser‐excited delayed fluorescence of tetracene crystals is discussed. It is shown to be sensitive to minute amounts (≪ 1 ppm) of trapping centers, probably pentacene, whose lifetime may have been mistaken for the free triplet lifetime. General equations for the decay of the host delayed fluorescence in the presence of traps, trap saturation, and bimolecular processes, are given; their application to tetracene yields trap parameters and a lower limit of the free triplet lifetime, in the crystals studied. The two‐photon generation rate constant of singlets at 6943 Å is about 1.5 × 10−27cm s, a value comparable to those found in naphthalene and anthracene at corresponding energies.