Different temperature dependences of photorefractive parameters of Ce-doped and Rh-doped BaTiO3

Temperature dependences of the total effective trap density N-eff and the e lectro-optic coefficient r(33) in Ce-doped and Rh-doped BaTiO3 were determi ned by two-beam coupling measurements. It was found that the effective trap density N-eff of BaTiO3:Ce increases whereas that of BaTiO3:Rh decreases w ith increasing temperature. The electro-optic coefficient r(33) Of both cry stals increases with temperature. The photorefractive response times were a lso measured and found to decrease with different rates as temperature incr eases in the two crystals. The results were discussed by using the two-cent re model for BaTiO3:Ce and three-charge-state model for BaTiO3:Rh. We found that the different temperature dependence of N-eff in the two crystals was due to the fact that the deep- and shallow-trap levels in BaTiO3:Ce are ca used by different impurity centres whereas those in BaTiO3:Rh are caused by different charge states of the same impurity centre.