LIGHT-INDUCED DARK DECAY AND SUBLINEAR INTENSITY DEPENDENCE OF THE RESPONSE-TIME IN COBALT-DOPED BARIUM-TITANATE

We report how the photorefractive propel-ties of cobalt-doped barium t itanate (BaTiO3) are influenced by deep and shallow traps. The light-i nduced dark decay of the space-charge field has two distinct time cons tants. The faster decay is due to the thermalization of charges from s hallow traps, whereas the longer decay is that from deep traps formed when BaTiO3 is doped with cobalt. This dopant substantially decreases the dark conductivity of BaTiO3 and thus increases the dark storage ti me. The power coefficient of the sublinear intensity dependence of the photorefractive response time progressively increases with the cobalt -dopant concentration. Apparently cobalt doping of the deep level elim inates the effect from the shallow level in BaTiO3. Although cobalt-do ped BaTiO3 has an increased effective trap density and thus an increas ed electrooptic gain, the response time and absorption are also increa sed, which thus decreases the photorefractive sensitivity.