Abstract
Under illumination with Ar+-, Kr+-laser or UV light, SrxBa1−xNb2O6 (SBN):Ce, SBN:Cr and pure SBN crystals show a light-induced absorption band around 2.1eV (600nm) with a considerable dichroism. This light-induced VIS-absorption exhibits nonlinear intensity dependence with saturation at high illumination strength. The temperature dependence of the light-induced absorption of the VIS-center for a specific illumination intensity shows for temperatures T<200K a nearly constant value, which however decreases rapidly at higher temperatures T>200K. The decay of the light-induced VIS-centers after the illumination is switched off is non-monoexponential and strongly depends on temperature. The decay rate of the VIS-centers is nearly zero at low temperatures T<100K, increasing rapidly above T>140K. The absorption and therefore the concentration of Ce3+- or Cr3+-centers in SBN crystals have been found to decrease with increasing illumination intensity at T=2K. At low temperatures T<140K under illumination (with Ar+-, Kr+-laser, UV light), in addition to the VIS-center absorption, a strong absorption band because of Nb4+ polarons [1], similar to absorption bands observed in reduced SBN crystals [2], appears in the NIR spectral region (λmax about 1.6μm). The bandshape of this Nb4+ polaron absorption extends with its tail into the visible region, overlapping with the absorption of the VIS centers. The Nb4+ polaron absorption decays rapidly even at low temperatures, and above T>140K no NIR absorption of these centers could be detected any more. A light-induced charge transfer model is proposed to explain the experimental results of the light-induced NIR and VIS absorption and the possible origin of the light-induced VIS-centers.
Published Version
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