Photoluminescence Spectral Change in Self-Assembled Layered Titanate Oxide Intercalated with Eu 3+
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0988-QQ03-07
Photoluminescence Spectral Change in Self-Assembled Layered Titanate Oxide Intercalated with Eu3+ Shintaro Ida, Ugur Unal, Kazuyoshi Izawa, Chikako Ogata, and Yasumichi Matsumoto Department of Nano Science and Technology, Graduate School and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan
ABSTRACT Titanate layered oxide intercalated with hydrated Eu3+ was synthesized by the electrostatic self-assembly deposition (ESD) method. The emission intensity of Eu3+ decreased rapidly with time during irradiation by UV light having energy higher than the band gap energy of the host Ti1.81O4 (TiO) layer. This is presumably due to the decrease in energy transfer from the host TiO layer to Eu3+ as a result of the change in the hydration state of water molecules surrounding Eu3+, which is caused by the hole produced in the TiO valence band. When irradiation was discontinued, the emission intensity gradually recovered. The recovery time increased when the water in the interlayer is removed by heat treatment. This indicates that the state of interlayer water changes during irradiation and returns to its initial state after discontinuation of irradiation. The excitation spectra changed drastically at any given wavelength upon irradiation with UV light. A comparison of the excitation spectra before and after irradiation reveals that only the excitation peak at around the irradiation wavelength decreased upon irradiation, as in the case of spectral hole burning. The hydration state of water molecules surrounding Eu3+ presumably changes depending on the irradiation wavelength.
INTRODUCTION Several types of layered oxides and TiO2 nanoparticles doped with Eu3+ ions show strong emission by an energy transfer process from the host matrix to the in-matrix Eu3+ ions [1-5]. In our previous study [6], it was discovered that the interlayer water molecules in the titanate layered oxide intercalated with Eu3+ ions strongly promote the emission of Eu3+ based on energy transfer from the titanate nanosheet layer to the Eu3+ ions, in contrast to the generally accepted view that the presence of water suppresses the emission of Eu3+ ions. In that case, the unique and special bonding state of water, as in hydrogen bonding in ice, seems to favor energy transfer for Eu3+ emission [6]. The water molecules in the interlayer are expected to impart other interesting properties in Eu3+ emission because of their unique bonding state. Thus, the present study examined in detail the photoluminescence properties of Eu3+ ions intercalated in the interlayer of titanate layered oxides during UV irradiation. It was found that the emission intensity of Eu3+ ions immediately decreases upon UV irradiation and that the excitation spectrum changes dramatically, as in the case of persistent spectral hole burning (PSHB) [7-9]. To the best of our knowledge, this is the first report on spectral change similar to PSHB for Eu3+ ions intercalated in layered oxides. In this paper, unique and interesting emission properties of the titanate
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