Anisotropic photoionization as alignment mechanism of axial iron centers in KTaO3

Photorecharging and optical alignment of FeTa4+--VO tetragonal complexes in KTaO3 crystal were detected by means of EPR technique. One detected the presence of mutual recharging of those two centers: FeK2+--Oi centre photoionization produced electron that was later captures by FeTa5+--VO centre. Irradiation by light with photon energy lower than 2.05 eV (FeK2+--Oi ionization threshold) - reverses this process. In both cases the absorption cross section depends on the mutual orientation of the centre axis and light polarization vector. As a result, FeTa4+--VO and FeK3+--Oi tetragonal centers in KTaO3 under the effect of polarized light exhibit orientation-sensitive photorecharging and for the defects with the given charge state the equal probability of distribution of their axes along three <100> directions is violated. This mechanism leads to the effect of alignment of the centers along (or transverse) the vector of light polarization