EPR of anatase titanium dioxide under uv light irradiation

Abstract

EPR spectra on a colorless single crystal of anatase titanium dioxide have sextuplet signals under irradiation of ultra violet (uv) light at temperatures of 100-40 K. The sextuplet is assigned to a paramagnetic species of S = 1/2 interacting with I = 5/2. The angular dependence of the sextuplet signals reveals anisotropic g-values of g xx = 2.026, g yy = 2.002 and g zz = 2.015. The intensities of the sextuplets reduce gradually with decrease in temperature. Only one signal can be observed at temperatures lower than 30K. This signal will originate from Ti 3+ in bulk.

Electron Paramagnetic Resonance and Optical Absorption of Yellow Anatase TiO2 Single Crystal

“…However, this signal suddenly disappears below 60 K. The temperature dependence of this weak signal is completely in accordance with that of the EPR signal observed on UV-irradiated colorless anatase crystals studied previously. 21) It was revealed that this signal is enhanced by UV light irradiation and has an anisotropic g-tensor. This signal must have a close relation to some defects that are introduced into the crystals on crystal growth and activated by UV light irradiation, or that are produced simply by UV light irradiation on the crystal surface.…”

UV irradiation effect on Al‐doped anatase titanium dioxide

“…These temperature dependences of signals A, B and C strongly resemble those of a nondoped anatase single crystal [2]. However, in the nondoped anatase single crystal, signal C is absent in the case without uv irradiation [2]. Figure 2 shows the orientation dependence of the EPR spectra of an Al-doped anatase single crystal under uv irradiation, measured at 90 K. A rotation of 90 degrees around the crystalline c-axis results in an interchange of sextuplets B and B', whereas in the rotation around the crystalline baxis, the relatively large splitting of the sextuplet seen at the lower magnetic field is observed.…”

“…The behaviour of signal C below 40 K under uv irradiation strongly resembles that in the case without uv irradiation with only a slight difference in intensity. These temperature dependences of signals A, B and C strongly resemble those of a nondoped anatase single crystal [2]. However, in the nondoped anatase single crystal, signal C is absent in the case without uv irradiation [2].…”

“…A small signal A is observed at about 3390 G in the spectra measured at RT and it shifts to a higher magnetic field with decreasing temperature. Signal A can be consistently observed regardless of uv irradiation, so this signal originates from a perpetual defect with paramagnetic spin [2]. At 100-60 K, a pair of sextuplets named signals B and B' can be observed in the range of 3315−3385 G under uv irradiation.…”

“…Interactions of photogenerated charge carriers with impurities and defects in titanium dioxide are of interest. Recently, our electron paramagnetic resonance (EPR) measurement (X-band) under uv light irradiation has revealed that a pair of sextuplets can be observed in the range of 3315-3385 G at 110-40 K for a nondoped colorless anatase single crystal [2]. Since the irradiation of uv light is indispensable for the observation of sextuplets, the photoinduced carriers are thought to participate in the generation of sextuplets.…”