Temperature dependences of β-ray-excited radioluminescence and uv-light-excited photoluminescence were measured in anthracene crystals. They depend on crystals, but their ratio shows the same characteristic in all of the crystals. Large temperature dependence of the ratio cannot be explained by the three relaxation processes of highly excited states, i.e. internal conversion and vibrational relaxation, autoionization (preionization) and exciton fission. It is expected by analyzing the data that there must exist a radiationless decay with an activation energy 0.048 eV in the relaxation manifolds. Predissociation to a geminate radical pair, which is followed by radiationless geminate recombination to an anthracene molecule or fission to isolated radicals, is considered as a competing process with the above three physical processes.
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