EPR on anatase titanium dioxide under uv-light irradiation
T. Sekiyaa*, H. Takedaa, N. Kamiyaa S. Kuritaa, T. Kodairab
a
Dept. Physics, Yokohama National University, Tokowadai 79-5,Hodogaya, Yokohama, 240-8501, Japan
b
Nanoarchitechtonics Research Center, AIST, Higashi 1-1-1, Tsukuba, Ibaragi, 305-8565, Japan
dI/dH
Titanium dioxide occurs naturally as the minerals rutile, anatase, and brookite. The
former two have been extensively investigated for photochemical applications because of
the photo-induced redox reactions of adsorbed substances and the photo-induced
hydrophilic conversion on its surface. Rutile has an indirect band-gap at 3.06 eV [1]
while anatase has a direct gap at about 3.3 eV [2]. Those photochemical functions are
active under ultra-violet (uv) light irradiation. Then, the difference in crystalline structure
has some effect on that in response under uv-light irradiation. We have grown anatase
single crystals by chemical vapor transport method [3]. Annealing the as-grown crystal
with pale-blue color under oxygen pressure results in conversion to a colorless crystal.
The colorless crystal has little defect because of the wide band gap energy and its high
resistivity [4]. In this study, we report EPR on the colorless anatase single crystal.
Figure 1 shows the temperature dependence of
RT
H//a
EPR signals of anatase under the irradiation of
uv-light at 3.40 eV. The weak signal observed
200K
at room temperatures can be also observed
150K
without uv-light irradiation, so that it
120K
originates from perpetual species. Two pairs
100K
of sextuplets can be observed at temperatures
90K
of 110-40 K under the uv-light irradiation.
80K
They show complex angular-dependence on
70K
the crystalline configuration with the external
60K
magnetic field. With a decrease in temperature,
50K
the sextuplets gradually decrease in their
intensities, while a new signal appears at
40K
about 60 K and increase in intensity.
30K
This work was financially supported in part by
20K
the Murata Science Foundation.
10K
* corresponding author e-mail: sekiya@ynu.ac.jp
3300
3320
3340
3360
3380
3400
3420
Magnetic Field (Gauss)
3440
References
1. J. Pascual, J. Camassel, H. Mathieu, Phys. Rev. B
Fig.1 Temperature dependence of EPR spectra
18, 5606 (1978).
of colorless anatase under uv-irradiation.
2. H. Tang, F. Lévy, H. Berger, P.E. Schmid., Phys.
Rev. B 52, 7771 (1995).
3. T. Sekiya, M. Igarashi, K. Ichimura, S. Kurita, J. Phys. Chem. Solids, 61, 1237 (2000).
4. T. Sekiya, T. Yagisawa, N. Kamiya, D.D. Mulmi, S. Kurita, Y. Murakami, T. Kodaira, J. Phys. Soc.
Jpn. 73, 703 (2004).