ИСТИНА

We have studied nitrogen doped microspheres (TiO2/MoO3, TiO2/WO3, TiO2/V2O5, TiO2/MoO3/V2O5, TiO2/WO3/V2O5, TiO2/MoO3/WO3, TiO2/MoO3/V2O5/WO3) using our new method based on EPR spectroscopy for constructing the band diagram of nanostructured semiconductors. Different paramagnetic centers (Ti3+, Mo5+,V4+, N•) were found in the microspheres depending on their composition. The EPR signal intensity of the revealed rad-icals was changing under illumination. We have measured the dependence of the EPR signal intensity of different paramagnetic centers on the photon energy (hν). Let us discuss as ex-ample the results obtained for the TiO2/MoO3/V2O5/WO3 samples. It was found that at values of the photon energy hν = 2.7 eV, an increase in the intensity of the EPR signal from Ti3+ centers occurs, and at hν = 1.55 eV, the EPR signal from N• radi-cals increases (TiO2 nanocrystals, Eg=3.2 eV). We suppose, taking into account the data of [2], that the defects are recharged under illumination due to impurity absorption: N- + hν → N• + e (in the conduction band); Ti4+ + hν →Ti3+ + h (in the valence band). It was found that at values of the photon energy hν = 2.8 eV, an increase in the intensity of the EPR signal from Mo5+ centers occurs (MoO3 nanocrystals, Eg=3.1 eV), and at hν = 2.1 eV, the EPR signal from V4+ radicals increases (V2O5 nanocrystals, Eg=2.5 eV). No paramagnetic centers were detected in WO3. Using the obtained values, we can estimate the position of the energy levels of these defects in the band gap [2]. This result is shown in Fig. 1.