Proton Polarization with Naphthalene Crystals by Integrated Solid Effect on Photoexcited Triplet State(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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We have carried out detailed systematic studies of relaxation effects, which contribute to a significant improvement in proton polarization in a single crystal of naphthalene doped with pentacene. The experiments have been performed in a magnetic field of 3kG at room temperature or at 77K and with a pulsed dye laser or a pulsed N_2 laser. We have found that a relaxation rate in the presence of irradiation with visible light (λ=595nm) is much smaller than that with ultraviolet light (λ=337nm) at room temperature, although the absorption rate of visible light is much larger than that of ultraviolet light. By cooling the crystal, the slow motion of the naphthalene molecules, which is a dominant relaxation process, can be suppressed. Surprisingly, we have found that the relaxation time at 77K in the presence of the dye laser becomes long, but still depends on the laser power. Our investigation has also indicated that both the longer relaxation time and the irradiation with the dye laser lead to a great improvement in the polarization of protons in the bulk of a crystal from 0.5% at room temperature to 32% at 77K.
社団法人日本物理学会の論文
2005-09-15