Temperature and Excitation Energy Dependence of the Photoionization of the F2 Center in 伪-Al2O3

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• 作者：Shogo Ikeda ; Takashi Uchino
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：February 27, 2014
• 年：2014
• 卷：118
• 期：8
• 页码：4346-4353
• 全文大小：493K
• 年卷期：v.118,no.8(February 27, 2014)
• ISSN：1932-7455

文摘

Photoionization spectra of the F₂ center in 伪-Al₂O₃ have been determined in the temperature region from 77 to 400 K by using reversible photoinduced interconversion phenomena of the F- and F₂-type centers. It has been shown that photoionization of the F₂ center is most effectively initiated by resonant photoexcitation of the F₂ center or by excitation with a 4.1 eV photon. The efficiency of photoionization increases with increasing temperature, demonstrating that a thermal process is involved for the electron to be promoted from the F₂-center excited states to the conduction band under the resonant (or near-resonant) excitation condition. Under excitation in the energy region higher than 4.8 eV, however, the photoionization efficiency of the F₂ center is hardly dependent on temperature, indicating that the direct photoionization of the F₂ center is possible in this excitation energy region. It has also been demonstrated that the temperature has a substantial effect on lowering the photoionization onset energy, which can be varied from 3.85 eV at 77 K to 3.60 eV at 400 K. This temperature dependence of the photoionization onset energy can be interpreted in terms of the strong coupling between the photoexited electron and the phonon modes of the crystal.