A new luminescence component was observed when anthracene crystals were excited by visible light under β-ray irradiation. It originates from the light-excitation of some excited state generated by β-ray irradiation. Though the spectrum agrees with that of fluorescence and the lifetime is about 7 ms, it is not the normal delayed fluorescence resulting from triplet-triplet annihilation. A remarkable difference from the luminescence which has ever been observed is the existence of a threshold in the intensity of excitation light.
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