Ca2+掺杂铌酸锶钡晶体的光折射变化特性研究

基于Ca2+掺杂铌酸锶钡晶体的透射特性,探讨了Ca2+在晶体中的电子行为机制,分析了Ca2+掺杂而引起的光致折射率变化特性.采用Michelson干涉装置测得了样品折射率随时间变化的特性曲线.实验结果分析表明,适当的ca2+掺杂可以有效改善铌酸锶钡晶体的光折射特性.     

铁电钾钠铌酸锶钡薄膜电光性能的研究

采用溶胶-凝胶法在氧化镁单晶衬底上制备了符合化学计量比的完全填充型铁电钾钠铌酸锶钡(KNSBN)薄膜，通过X射线衍射，摇摆曲线，X射线Φ扫描，扫描电子显微镜等方法研究了薄膜的微结构，采用Adachi法研究了薄膜的电光特性. 实验发现，KNSBN薄膜在氧化镁(001)单晶衬底上沿c轴外延生长，K⁺，Na⁺的引入有效地提高了薄膜的横向电光系数r₅₁. 成分为K_0.2Na_0.2Sr_0.24Ba_0.56Nb₂O₆, K_0.2Na_0.2Sr_0.6Ba_0.2Nb₂O₆, K_0.2Na_0.2Sr_0.72Ba_0.08Nb₂O₆的三种KNSBN薄膜的r₅₁值分别为108.52pm/V, 119.98pm/V, 126.96pm/V，r₅₁的数值随Sr²⁺含量增加而增大. 关键词： 横向电光系数 钾钠铌酸锶钡 外延生长     

掺铜钾钠铌酸锶钡晶体自泵浦相位共轭研究

用掺铜钾钠铌酸锶钡晶体制成猫式(cat)自泵浦相位共轭器,共轭光反射率高达63%.增加掺铜量,晶体在红光波段效应增强.本文研究了掺杂浓度、激光波段与该器件性能的关系.     

利用光衍射效应探测周期极化微结构晶体

以光栅衍射理论为基础，从理论上分析研究了微结构晶体衍射效率与占空比和折射率的关系.采用波长为532nm，最大功率为80mW 的连续激光为光源，分别对周期极化掺镁铌酸锂微结构晶体和周期极化同成分铌酸锂微结构晶体的占空比及极化反转引起的折射率变化进行了测试.测试结果表明，掺镁铌酸锂晶体周期极化反转所引起的折射率改变量大于同成分铌酸锂晶体极化反转所引起的折射率变化. 关键词： 光栅衍射 占空比 折射率变化     

Ca2+掺杂对NaYF4:Yb,Er微米晶上转换发光性能的影响

采用柠檬酸钠辅助的水热方法制备了一系列不同Ca²⁺含量的Ca²⁺/Yb³⁺/Er³⁺共掺的NaYF₄微米片。利用透射电子显微镜(TEM)、X射线衍射分析(XRD)、发光光谱等测量手段对样品进行了形貌、晶相、发光性质的表征。样品在980 nm激光泵浦下,可以观察到强的上转换绿色荧光。在Ca²⁺的摩尔分数从0增加到8%的过程中,紫外到可见的上转换发光随着Ca²⁺浓度的增加而显著增强。这是由于Ca²⁺的掺杂导致了晶体内部的不对称性,同时也提高了晶体的结晶性。     

Er3+/Yb3+共掺NaYF4/LiYF4微米晶体的上转换荧光特性

采用水热法成功制备了Er³⁺/Yb³⁺共掺杂的NaYF₄和LiYF₄微米晶体. 通过X射线衍射仪和环境扫描电子显微镜对样品的晶体结构及形貌进行表征. 实验结果表明: 六方相NaYF₄微米晶体为棒状结构, 而四方相LiYF₄微米晶体则为八面体结构. 在近红外光980 nm激发下, NaYF₄:Yb³⁺/Er³⁺和LiYF₄:Yb³⁺/Er³⁺ 微米晶体均展现出很强上转换荧光发射. 且NaYF₄:Yb³⁺/Er³⁺微米晶体的荧光发射强度大约是LiYF₄:Yb³⁺/Er³⁺微米晶体的2倍, 但红绿比明显较低. 根据荧光光谱, 并借助激光光谱学及发光动力学深入探讨基质变化及表面修饰剂乙二胺四乙二酸(EDTA)对荧光特性的影响. 实验结果发现: 影响荧光强度的主要因素是基质环境的局域对称性, 而导致不同红绿比则是由于样品表面较多的EDTA分子所引起. Er³⁺掺杂的NaYF₄和LiYF₄ 微米晶体呈现出很强的绿光发射可被应用于全色显示, 荧光粉和微光电子器件中.     

Mn^4＋在钾钠铌酸锶钡晶体中的能态

测得了光折变材料锰掺杂的钾钠铌酸锶钡晶体（ＫＮＳＢＮ：Ｍｎ）的透过率，给出了晶体的能态结构，按配位场理论讨论了Ｍｎ＾４＋的作用机制，从微观结构上解释了ＫＮＳＢＮ：Ｍｎ的光学二极管效应。     

准位相匹配铌酸锂波导倍频特性分析与优化设计

用标量有限元方法计算了周期性极化的铌酸锂光波导中模折射率和模场分布,并在计算中引入铌酸锂晶体折射率与温度变化的关系,分析了准位相匹配铌酸锂波导倍频效率与极化反转光栅周期、基频光波长、波导器件温度等关系.理论分析与实验结果符合得很好.在此基础上,分析了波导制作参数与倍频效率、光栅周期与晶体温度,以及温度带宽与光栅通光方向长度等关系,进而对铌酸锂波导倍频器件进行优化设计. 关键词： 铌酸锂 光波导 准位相匹配 有限元     

铌酸锶钡光折变表面电磁波实验

在实验中观察到扩散和漂移机理下在光折变晶体铌酸锶钡（SBN）与空气的界面形成的光折变表面电磁波. 这种表面电磁波形成的条件是：入射光束与界面成55°角入射，信号光与背景光比值越大越有利于形成表面电磁波，外加电场越大表面电磁波就越强. 关键词： 表面电磁波 扩散和漂移机制 SBN     

用正电子湮没研究钙钛矿结构压电陶瓷中的点缺陷

用正电子湮没寿命谱技术对有意掺杂的或被杂质替代的钙钛矿结构压电陶瓷中的点缺陷进行了研究.掺杂了La³⁺的PbTiO₃，掺杂了Sr²⁺，Cd²⁺和La³⁺的Pb(Mg_1/3Nb_2/3)_0.375Ti_0.375Zr_0.25O₃，掺杂了Ca²⁺的BaT 关键词：     

Optical homogeneity,defects, and photorefractive properties of stoichiometric,congruent, and zinc-doped lithium niobate crystals

Using the laser-conoscopy method, the photorefractive light-scattering method, and the Raman light-scattering method, we have studied the structural and optical homogeneities and photorefractive properties of (i) stoichiometric lithium niobate crystals (LiNbO₃(stoich)), which were grown from a melt with 58.6 mol % of Li₂O; (ii) congruent crystals (LiNbO₃(congr)); and (iii) congruent crystals that were doped with Zn²⁺ cations (LiNbO₃:Zn; [Zn] = 0.03–1.59 mol %). We have shown that the speckle-structure of the photorefractive light scattering in all the crystals is three-layer. The shapes of the second and third layers repeat in general the shape of the first layer. We have shown that the differences that are observed between the Raman spectra, the photorefractive light scattering, and the conoscopic patterns of the examined crystals are caused by the fact that defects are distributed inhomogeneously over the volume of these crystals and that Zn²⁺ cations are incorporated inhomogeneously into the lattice. This leads to the appearance of local changes in the elastic characteristics of the crystal and to the appearance of mechanical stresses, which locally change the optical indicatrix and, correspondingly, the conoscopic pattern and the Raman spectrum.     

Effect of rhodium doping on the photorefractive properties of BCT crystals at 850 nm

We present an experimental investigation of the photorefractive properties of rhodium-doped barium calcium titanate (BCT) crystals of the congruent melting composition Ba_0.77Ca_0.23TiO₃. Considering the results previously obtained on this crystal in the visible region, it should be a good alternative to BaTiO₃. Nevertheless, many applications use infrared light. Therefore we present here a study of rhodium-doped BCT crystals at 850 nm. This wavelength is of special interest as it is in the spectral range of laser diodes. Rhodium doping is expected to enhance the sensitivity of the crystal in the infrared as is the case for BaTiO₃.We first noticed that BCT:Rh crystals are sensitive at this wavelength as expected. Furthermore, the photorefractive properties are interesting in terms of photorefractive gain, with a gain as high as 3 cm^-1 with ordinary polarization. This study has also put forward the fact that rhodium is not the only defect that participates in the photorefractive effect. Indeed, a large quantity of iron seems to be present in the BCT crystals and to participate in the photorefractive effect.An Erratum to this article can be found at     

Photorefractive light scattering in lithium niobate crystals doped with Mg2+, B3+, Y3+, and Ta5+

We have investigated the photorefractive (photoinduced) light scattering in lithium niobate single crystals: LiNbO₃, LiNbO₃:B, LiNbO₃:Y(0.46 mas %), LiNbO₃:Y(0.24):Mg(0.63 mas %), and LiNbO₃:Ta(1.13):Mg(0.0109 mas %) that were grown from congruent melts. We have found that the shape of the speckle structure of this scattering and the kinetics of the development of its indicatrix depend substantially on the type of the impurity dopant in the lithium niobate crystal. We have observed that, upon laser irradiation of crystals doped with Y³⁺, Ta⁵⁺:Mg²⁺, and Y³⁺:Mg²⁺, the shape of their scattering indicatrix changes with time. At the same time, the LiNbO₃:B crystal is characterized by a complete absence of time changes in its speckle structure, which indicates that the photorefractive effect in this crystal is substantially lowered.     

Spatiotemporal dynamics of Ca2+ signaling and its physiological roles

Changes in the intracellular Ca²⁺ concentration regulate numerous cell functions and display diverse spatiotemporal dynamics, which underlie the versatility of Ca²⁺ in cell signaling. In many cell types, an increase in the intracellular Ca²⁺ concentration starts locally, propagates within the cell (Ca²⁺ wave) and makes oscillatory changes (Ca²⁺ oscillation). Studies of the intracellular Ca²⁺ release mechanism from the endoplasmic reticulum (ER) showed that the Ca²⁺ release mechanism has inherent regenerative properties, which is essential for the generation of Ca²⁺ waves and oscillations. Ca²⁺ may shuttle between the ER and mitochondria, and this appears to be important for pacemaking of Ca²⁺ oscillations. Importantly, Ca²⁺ oscillations are an efficient mechanism in regulating cell functions, having effects supra-proportional to the sum of duration of Ca²⁺ increase. Furthermore, Ca²⁺ signaling mechanism studies have led to the development of a method for specific inhibition of Ca²⁺ signaling, which has been used to identify hitherto unrecognized functions of Ca²⁺ signals.     

Manifestation of a Photorefractive Effect in the Raman Scattering Spectra of Lithium Niobate Crystals of Variable Composition

Using the Raman scattering spectra, we investigated the ordering of the structural units in the cation sublattice and the photorefractive properties of lithium niobate single crystals of variable composition, i.e., nominally pure ones with different Li/Nb ratios and those doped with the nonphotorefractive cations Mg²⁺, Gd³⁺, and Y³⁺. It is shown that at low concentrations of Mg²⁺, Gd³⁺, and Y³⁺ the magnitude of the photorefractive effect is substantially determined by the ordering of the structural units of the cation sublattice. It has been found for the first time that the intensity of the line corresponding to the bridge valence vibrations of oxygen atoms in the octahedrons of NbO₆ is sensitive to the dipole ordering of the cation sublattice of the crystal. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 611–614, September–October, 2005.     

Charge transport in highly iron-doped oxidized lithium niobate single crystals

The photorefractive properties of highly iron-doped lithium niobate crystals in as-grown and completely oxidized states are investigated. Iron concentrations range from 0.5 to 3 wt. %. Measurements of light-induced refractive-index changes, two-beam coupling gain, bulk-photovoltaic current densities, and conductivities are performed with visible light. Absorption spectra and the bulk photovoltaic currents are used to determine the Fe²⁺ concentration. The dark conductivity confirms the tunneling model for charge-carrier migration. Beam-coupling experiments as well as photocurrent measurements with highly oxidized samples indicate that the one-center model is valid in such highly doped crystals, but that hole conductivity dominates the charge transport. PACS 72.20.Jv; 72.40.+w; 81.40.Tv     

Photorefractive properties of iron-doped lithium tantalate crystals

Iron-doped lithium tantalate crystals are grown by the Czochralski method and their photorefractive properties are examined with holographic methods. Dynamic range, holographic sensitivity, photoconductivity, and dark storage time are measured in dependence on the iron concentration and light intensity. The largest refractive-index change for ordinarily polarized light is 3.5×10^-4, in comparison with 6.2×10^-4 for iron-doped lithium niobate. Due to a small mobility of protons the dark storage time of holograms in lithium tantalate is larger than that in lithium niobate. PACS 42.40.Pa; 42.70.Ln     

Origin of dark holographic scattering patterns in photorefractive crystals

We explain the origin of recently reported dark parametric holographic scattering patterns observed in photorefractive strontium–barium niobate (SBN) and barium–calcium titanate (BCT) crystals. Taking into account the model for parametric four-wave-mixing processes in photorefractive crystals, exponential gain factors are presented for the scattering patterns and compared with the gain for the scattering background. We interpret the dark scattering patterns as a result of counteracting energy-transfer processes. PACS 42.65.Hw; 42.70.Nq     

Nonlinear response of photorefractive lithium tantalate and niobate at acoustic frequencies

An amplification of the intensity of pump oscillations is observed experimentally at frequencies from 100 Hz to 1 kHz during photoinduced light scattering and holographic-type parametric scattering in photorefractive lithium tantalate and niobate. Possible ways are analyzed for explaining the existence of a photorefractive response in these crystals over times of 10⁻²–10⁻³ s, which are five orders of magnitude shorter than the Maxwell time. Zh. éksp. Teor. Fiz. 112, 1490–1498 (October 1997)     

Optical properties of LiNbO3:Mg(5.21 mol %) and LiNbO3:Fe(0.009 mol %):Mg(5.04 mol %) crystals

Using methods of electronic spectroscopy, laser conoscopy, photoinduced (photoreactive) light scattering, and Raman light-scattering spectroscopy, we have studied the optical homogeneity, optical transmission, and photorefractive properties of single crystals LiNbO₃:Mg(5.21 mol %) and LiNbO₃:Fe(0.009 mol %):Mg(5.04 mol %) that were grown from congruent melts. We have ascertained that doping with “nonphotorefractive” Mg²⁺ cations causes suppression of the photorefractive effect in a lithium-niobate crystal. Upon double doping (Fe:Mg), if the concentration of Mg²⁺ cations exceeds the threshold concentration, the photorefractive effect is almost not observed and the presence of “photorefractive” Fe cations does not affect the photorefractive effect as strongly as in congruent crystals doped with Fe.