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The fluorescent spectra of crystals of naphthalene and anthracene with added "impurities" of naphthacene and 1,2,5,6-dibenzanthracene, under x-ray excitation Lipsett, Frederick Roy


When a crystal of anthracene with a small added "impurity" of naphthacene is excited by X-radiation or ultraviolet light the fluorescent spectrum includes or consists almost totally of naphthacene bands. The energy absorbed by the anthracene is said to have been transferred to the naphthacene. The same result is obtained with certain other "impurities" and matrix compounds. Although this process had been known to exist for some time, no detailed quantitative experiments had been performed. The author used an arrangement including a Beckman Model DU Quartz Spectrophotometer used as a mono-chrometer and a 931-A photomultiplier tube as a detector to obtain fluorescent spectra. This arrangement combined very great sensitivity with great convenience of operation. The spectra of crystals of anthracene with naphthacene, naphthalene with naphthacene, and naphthalene with 1,2,5,6-dibenzanthracene were obtained. The maximum intensity of fluorescence of the impurity bands occurred at 2.93 x 10ˉ⁴ moles naphthacene per mole anthracene in the crystals of anthracene plus naphthacene: at 3.38 x 10ˉ⁵ moles naphthacene per mole naphthalene in the crystals of naphthalene plus naphthacene: and at 1.01 x 10ˉ⁴ moles 1,2,5,6-dibenzanthracene per mole naphthalene in the crystals of naphthalene plus 1,2,5,6-dibenzanthracene. The fluorescent spectrum of a crystal of anthracene was obtained using first X-ray excitation and then ultra-violet excitation. The two sources of excitation gave rise to different spectra. A theory of the mechanism of energy transfer and a hypothetical set of energy levels for the crystals with added impurities are given. The method used to grow some of the crystals used in this research is given in an Appendix.

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