Influence of nonstoichiometry and iron doping on optical absorption in   KNbO3 single crystal
  Single crystals of KNbO3 and KNbO3 : Fe have been grown using the flux method at various technological conditions. The investigations of optical absorption of these crystals were carried out. Marked influence of technological conditions and doping with iron on optical absorption has been found. Observed changes of the absorption spectra are associated with lattice defects arising due to nonstoichiometry and/or doping. 
M. Milata, K. Wojcik, and K. Zieleniec (Institute of Physics,   University of Silesia)