| Co-Investigator(Kenkyū-buntansha) |
NARUSE Norio National Institute of Advanced Industrial Science and Technology, Senior Researcher, 関西センター, 主任研究員
HAYAKAWA Tomokatsu Nagoya Institute of Technology, Faculty of Engineering, Research Associate, 工学研究科, 助手 (00293746)
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| Research Abstract |
Persistent spectral hole burning (PSHB) phenomenon of Eu^<3+> and Sm^<2+> ions is one of the most significant optical properties for use in high-density frequency-domain optical data memory. For practical use, high temperature PSHB and stable hole are required. As a host material, glasses are thought to be more favorable than crystals, because of their wide inhomogeneous width, compositional variety and easy mass production. In this work, we studied the preparation of PSHB glasses doped with Eu^<3+> and Sm^<2+> ions using a sol-gel method and the PSHB properties of these glasses treated with different conditions. The conclusions of our research are summarized as follows ;
(1) PSHB was observed on the excitation spectra of the ^7F_0→^5D_0 transition of the Eu^<3+> and Sm^<2+> ions-deped glasses.
(2) The efficiency of hole-burning, burned at low temperature 〜77K, was proportionally increased with the content of OH groups surrounding the rare-earth ions. The proposed mechanism for hole-burn
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ing was the optically activated rearrangement of the OH bonds surrounding the rare-earth ions. The burned-hole was thermally refilled and erased above 〜200K.
(3) The glasses obtained by heating in H_2 gas showed PSHB up to room temperature. When heated in H_2 gas, the H_2 molecules react with oxygen ions to form H_2O. Removal of the generated H_2O causes the number of oxygen ions surrounding rare-earth ions to decrease, resulting into the reduction of the ions. The hole burning in the H_2-treated, glasses was performed by the electron transfer between the rare-earth ions and the trapping centers.
(4) The glasses which were irradiated with x-ray also showed room temperature PSHB. It was found that the rare-earth ions are reduced into the divalent state by electron transfer from the oxygen defect center. The hole defect centers are trapped in oxygen ions bound with Al^<3+> ions. The spectral hole burning of the x-ray irradiated glasses could be burned by the reverse reaction of the reduction of the rare-earth ions. A short distance between the Sm^<2+> and oxygen defect centers brought a high-speed hole burning, that is, 30 times faster than in a similar H_2 gas treated glass. This fast formation of PSHB was contributed to the formation of the Sm^<2+> and hole center in oxygen ions.
(5) PSHB was also observed in the femtosecond laser-irradiated Sm^<2+> ions-doped Al_2O_3-SiO_2 glasses. The hole-burning efficiency was superior to that of Sm^<2+> ions in the H_2-treated glasses and comparable to that in x-ray irradiated glasses. prepared by the sol-gel method.
(6) Two different mechanisms were proposed for the PSHB in the Sm^<2+>-doped Al_2O_3-SiO_2 glasses. In the H_2-gas treated glass, the Sm^<2+> ions are stable to bond with the defect free oxygen ions. PSHB is formed by the ionization of the Sm^<2+> and the capture of the released-electron in the Sm^<3+> ions. On the other hand, in the x-ray or laser irradiated glass, the electrons excited from the Sm^<2+> are trapped in the hole-centers in the neighboring oxygen. A short distance between the Sm^<2+> and the oxygen defect center makes fast hole formation. These fast and high efficient hole burning glass become possible to realize high density memory. Less
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