A study on the photorefractive effect in relaxor ferroelectric crystals

1.晶体生长和样品制备(a)我们生长出了弛豫铁电晶体0.91Pb(Zn_<1/3>Nb_<2/3>)O_3-0.09PbTiO_3。(b)晶体被切割、抛光和极点。首次在铅基弛豫铁电晶体中观察到光折变效应。(c)以不同浓度掺杂Fe， Mn和Rh的相同晶体生长，并评估其光折变特性。(d)这些晶体中的光散射显著减少[110]。这也是我们在这个项目中的最初发现。(a)测量所有样品的电光系数为200 pm/V。(b)测量了未掺杂和掺杂晶体的光折变响应速度和双波混频增益。最大双波混频增益为20cm^<-1>，是块体铁电晶体中最大的增益之一。(c)通过ICP测量未掺杂晶体，未检测到杂质。根据这一结果，一些缺陷水平被认为是光折变中心。(d)从两波混频中能量传递的方向和电光系数的符号，确定了主要载流子为空穴。(e) Fe和Rh掺杂增强了光折变效应。双光束耦合增益加倍。(f) Fe掺杂和Rh掺杂晶体的光致变色。这说明了双色书写非易失性全息记录方法的可行性。(g)在大于600 nm的波长范围内，铑掺杂晶体的光折变效应增强。(h)检测到晶体电闭时的体光伏效应，并观察到衍射效率的提高。

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.