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The formation of the photo-polaronic excitons in ABO_{3} perovskite typeoxides has been detected experimentally by means of the photoinduced electronparamagnetic resonance studies of KTa_{0.998}Nb_{0.012}O_{3} crystals. Thecorresponding microwave X-band spectrum at T < 10 K consists of a narrow,nearly isotropic signal located at g ~ 2 and a strongly anisotropic component.The first signal, which has a rich structure due to hyperfine interactions withthe lattice nuclei, is attributed to the single trapped charge carriers: theelectrons and/or the holes. The anisotropic spectrum is caused by the axialcenters oriented along the C_{4} pseudo-cubic principal crystalline axes. Thespectrum angular dependence can be described well by an axial center with S =1, g_{\parallel) = 0.82, g_{\perp} = 0.52 and D = 0.44 cm^{-1}. The anisotropicspectrum is attributed to the Nb^{4+}-O^{-} polaronic excitons. The temperaturedependence of the anisotropic component is characterized by two activationenergies: the internal dynamics activation E_{a1} = 3.7\pm0.5 meV, which makesthe EPR spectrum unobservable above 10 K, and the destruction energy E_{a2} =52\pm4 meV. By comparing the anisotropic photo-EPR spectrum and thephotoinduced optical absorption temperature dependencies, we found that theNb^{4+}-O^{-} polaronic excitons also manifested themselves via the ~0.7 eVwide absorption band arising under UV light excitation in the weaklyconcentrated KTaO_{3}:Nb crystals.

Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}