LIGHT-INDUCED VIS AND NIR ABSORPTION IN SBN, CE AND SBN, CR CRYSTALS

Congruent Sr0.61Ba0.39Nb2O6 crystals doped with Ce or Cr are investiga ted under immersion techniques with Fourier spectroscopy in a wide spe ctral range from UV to FIR. for enhanced light-induced absorption effe cts leading to photorefractive properties. Spectroscopic evidence is f ound for the 3+ majority state (FIR Ce3+ spin-orbit and crystal field split 4f transitions and Cr3+ R-lines). The broad polaronic Nb4+ absor ption (at 0.78 eV/1.6 mu m), known from reduced SBN, appears also unde r Ar+-laser illumination at low temperatures (T<140 K). With red Kr+-l aser (647 nm) illumination the polaronic Nb4+ absorption for SBN doped with Cc is found to be several orders of magnitude larger than for SB N:Ce, indicating the enhanced red sensitivity of this material. The in tervalence transition model Ce3++Nb5+ --> Ce4++Nb4+ must be extended t o accomodate new experimental features like nonlinear intensify depend ence, non-monoexponential decay kinetics and complicated temperature d ependence of the light-induced absorption in the NIR and of new light- induced broad absorption bands in the uv-visible region.