Light-induced VIS and NIR absorption in SBN : Ce and SBN : Cr crystals

Abstract

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