A study on the photorefractive effect in relaxor ferroelectric crystals

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1.Crystal growth and sample preparation(a)We have grown relaxor ferroelectric crystals, 0.91Pb(Zn_<1/3>Nb_<2/3>)O_3-0.09PbTiO_3. (b)The crystals are cut, polished, and poled. The photorefractive effect is observed in Pb based relaxor ferroelectric crystals at the first time. (c)Same crystals, doped with Fe, Mn, and Rh were grown with various concentrations, and their photorefractive properties were evaluated. (d)Light scattering in these crystals were dramatically reduced by [110]. It is also our original finding in this project.2.Evaluation of the photorefractive properties(a)Electro-optic coefficient was measured as 200 pm/V for all the samples. (b)Photorefractive response speed and the two-wave mixing gain were measured for undoped and doped crystals. The maximum two-wave mixing gain was 20cm^<-1>, which was one of the largest value in the bulk ferroelectric crystals. (c)Through the ICP measurement of undoped crystals, no impurities are detected. Some defect levels supposed to acting as photorefractive centers from this result. (d)From the direction of the energy transfer in two-wave mixing and the sign of the electro-optic coefficient, the main carrier was determined to be the holes. (e)Photorefractive effects were enhanced by Fe and Rh doping. Two beam coupling gain was doubled. (f)Photochromisms were observed in Fe doped and Rh doped crystals. This suggest that the feasibility of the non-volatile holographic recording with two color writing method. (g)Photorefractive effects were enhanced in the wavelength range larger than 600 nm in Rh doped crystals. (h)The bulk photovoltaic effect are detected and the enhancement of the diffraction efficiency was observed when the crystal was electrically closed.