Investigations of photochromic centers and impurities in nominally pure monocrystals of KTaO3 and K1-xLixTaO3 (where x was equal to 0.016, 0.02 or 0.03) were carried out by using electron spin resonance methods. In all of the investigated K1-xLixTaO3 samples, the axial symmetry spectrum of Fe3+ which substituted for K+ [Feax3+(K)], the cubic symmetry spectrum of Fe3+ which substituted for K+ [Fec3+(K)], and of Ni3+ which substituted for Ta5+ [Nic3+(Ta)] were observed at temperatures below 60K. After illumination with light with a wavelength of between 365 and 436nm, several electron spin resonance spectra appeared. Each one had a characteristic annealing temperature between 25 and 120K. In K1-xLixTaO3 samples, the Feax3+(K) spectrum disappeared and the intensities of the Fec3+(K) and Nic3+(Ta) spectra decreased. In the case of nominally pure KTaO3, the Feax3+(K) and Feax+(K) spectra which were observed before illumination, disappeared after illumination. A gradual restoration of these spectra in both materials was observed at temperatures above 25K when some of the photo-induced spectra disappeared. One of the photo-induced spectra was shown to be due to O- in both materials.

V.V.Laguta, M.D.Glinchuk, I.P.Bykov, J.Rosa, L.Jastrabík, R.S.Klein, G.E.Kugel: Physical Review B, 1995, 52[10], 7102-7