LUMINESCENCE AND ESR SPECTROSCOPY OF KTAO3 CRYSTALS

Nominally pure KTaO3 single crystals and crystals slightly doped with iron were investigated by luminescence and ESR methods. In the doped s amples two different zero-phonon lines were found in the luminescence spectra at 14567 and 15149 cm(-1) under excitation at 470 and 395 nm, respectively. The latter was observed for the first time. The second e mission was ascribed to Fe+ impurities substituted for K+ with an off- center shift along the [100] directions, revealed by ESR measurements. The interpretation of phonon frequencies appearing in the vibronic sp ectra of KTaO3 is performed for both emissions. Analysis of ESR. and l uminescence spectra of all the samples has shown the existence of anot her symmetry breaking defect-axial Fe3+ substituted for K+.