The Photoconductivity of the Titanium Dioxide Crystal

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Abstract
The photoconductivity of titanium dioxide (rutile type) synthesized by the flame-fusion method was studied. The photoconductivity spectra showed three peaks. The first is the maximum response around the edge of the fundamental absorption of rutile; the second is the peak at 630 mμ (1.98 eV), and the third is the broad-band spectra in the near infrared region of 1.0–1.9 μ. From the facts that Fe is found by chemical analysis to be a major impurity in rutile, that the peak at 630 mμ is enhanced by the increase in Fe concentration from 0.006 mol% to 0.02 mol%, and that the infrared quenching band of photoconductivity is observed at 1.23 μ (1.01 eV) in Fedoped rutile, it is concluded that this peak at 630 mμ results from the excitation of the electron from the Fe3+ level. The broad-band spectra at 1.0–1.9 μ are enhanced by the reduction and are decreased by the oxidation of the crystal, so these excitation spectra are ascribed to lattice defects originating from the non-stoichiometry of TiO2. These defects have much influence on the photoconductivity of rutile, i. e., on the relation between the photocurrent and the electrical applied field, and on the change the photocurrent versus the time.

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