同成分铌酸锂晶体中反位铌的扩散研究

通常商业使用的同成分铌酸锂晶体(CLN)是固液同成分共熔点配比,其Li2O含量约为48.6mol;,晶体中存在大量的锂空位和反位铌等本征缺陷,进而影响了晶体的电光系数、折射率、光折变等性能.研究表明,将缺锂的晶体在高温、富锂气氛下进行扩散处理可获得接近化学计量配比的铌酸锂晶体(nSLN),这种方法获得的nSLN晶体光学质量高,且技术简便、成本低,具有实际应用价值.本文分析了富锂气氛下CLN晶体扩散过程中反位铌的扩散机制和扩散路径,认为反位铌在扩散过程中将迁移到晶体外部,并通过CLN晶片的单边扩散进行了验证.     

系列铌酸锂晶体在电光调Q激光系统中的激光损伤性能研究

搭建了一套1064 nm波段的电光调Q激光系统,并对其能量、脉宽、光斑质量等进行了表征.在该激光系统环境中分别测试了扩散法制备的掺杂1 mol;氧化镁的近化学计量比铌酸锂(Mg1 SLN)晶体、名义纯同成分铌酸锂晶体(CLN)及掺杂5mol; MgO的铌酸锂(Mg5LN)晶体的激光损伤性能.结果 表明,在该调Q激光工作环境下,当波长1064 nm;脉宽为9.8 ns、频率为1 Hz时,Mg1 SLN晶体、Mg5 LN晶体和CLN晶体多个测试点发生激光损伤时对应的功率密度的平均值分别为1141 MW/cm2、874 MW/cm2和651 MW/cm2.     

高温下锂离子在低掺镁铌酸锂晶体中的扩散（英文）

研究了高温富锂气氛下锂离子在低掺镁铌酸锂晶体中的扩散。采用气相输运平衡法制备了掺杂1mol%MgO的不同锂含量的铌酸锂(Mg1LN)晶体,采用热分析仪测试了晶体的居里温度。制备了一系列不同锂含量的Mg1LN多晶料,拟合了晶体锂含量与居里温度的关系。采用Boltzmann-Matano法求解了扩散方程。结果表明,扩散温度为1100℃时,Mg1LN晶体中锂离子扩散系数为3.2×10~(-9)~13.0×10~(-9)cm~2/s,当扩散温度为1145℃时锂离子扩散系数约是1100℃时扩散系数的三倍。因此,适当提高扩散温度是提高气相输运平衡法制备近化学计量比低掺镁铌酸锂晶体效率的有效办法.     

高温下锂离子在低掺镁铌酸锂晶体中的扩散

研究了高温富锂气氛下锂离子在低掺镁铌酸锂晶体中的扩散.采用气相输运平衡法制备了掺杂1mol; MgO的不同锂含量的铌酸锂(Mg1LN)晶体,采用热分析仪测试了晶体的居里温度.制备了一系列不同锂含量的Mg1LN多晶料,拟合了晶体锂含量与居里温度的关系.采用Boltzmann-Matano法求解了扩散方程.结果表明,扩散温度为1100 ℃时,Mg1LN晶体中锂离子扩散系数为3.2×10-9~13.0×10-9 cm2/s,当扩散温度为1145 ℃时锂离子扩散系数约是1100 ℃时扩散系数的三倍.因此,适当提高扩散温度是提高气相输运平衡法制备近化学计量比低掺镁铌酸锂晶体效率的有效办法.     

四价掺杂铌酸锂晶体抗光折变性能研究

我们在同成份铌酸锂晶体中掺入四价离子铪,生长了掺杂浓度分别为2、4、6mol;的掺铪铌酸锂系列晶体.掺铪浓度达到4mol;时,晶体的抗光损伤能力为5×105W/cm2,比同成份纯铌酸锂晶体提高了4个数量级.应用全息法测得掺4、6mol;铪的铌酸锂晶体最大折射率变化为8.7×10-6,与高掺镁(6.5mol;)铌酸锂晶体的类似.晶体的红外吸收谱和紫外-可见光吸收谱也显示,掺杂浓度为4mol;时具有明显的阈值特征.由此可以确定铪离子在铌酸锂晶体中的阈值浓度约为4mol;.     

Cr∶LiNbO_3及Cr,Fe∶LiNbO_3晶体热释电系数提高的研究

生长了掺杂量分别为0.2mol%、0.5mol%的掺铬同成分配比铌酸锂晶体和掺铬0.2mol%、铁0.04mol%的双掺同成分配比铌酸锂晶体。利用动态电流法测试了它们的热释电系数。在同样的测试条件下,与未掺杂的同成分铌酸锂晶体相比较,掺铬铌酸锂(Cr∶LiNbO3)晶体和铬、铁双掺铌酸锂(Cr,Fe∶LiNbO3)晶体的热释电系数明显提高。同时对掺杂提高晶体热释电系数的机理进行了探讨。     

高掺锌/镁铌酸锂薄膜的光电性质

室温下采用射频磁控溅射(RFMS)技术在玻璃与硅基板上分别沉积了纯铌酸锂LN薄膜、高掺锌(6%,摩尔分数,下同)LN∶ZnO薄膜和高掺镁(5%)LN∶MgO薄膜,并在575 ℃条件下退火进一步提高薄膜的结晶度。通过原子力显微镜(AFM)、X射线衍射(XRD)、紫外可见吸收(UV-Vis)和椭偏仪等测试研究了三种铌酸锂薄膜的形貌、结构和光学性质。XRD分析表明掺杂铌酸锂薄膜和纯铌酸锂薄膜具有相同的生长取向,AFM、XRD、UV-Vis测试结果表明,掺杂将增大铌酸锂薄膜的晶粒尺寸,光学带隙的红移现象与晶粒尺寸相关,且掺Mg的影响大于掺Zn。此外利用霍尔效应测试仪研究了LN、LN∶ZnO和LN∶MgO薄膜的电学性质,测试结果表明三种薄膜均为n型半导体,其中LN∶MgO薄膜电导率的变化趋势不同于LN∶ZnO和LN薄膜,且发现温度在18~50 ℃范围内,随着温度的升高,LN∶MgO薄膜的电导率变化微小,而LN∶ZnO和LN薄膜的电导率逐渐增大。     

铌酸锂晶体的光折变效应

铌酸锂(LiNbO₃, LN)是一种多功能多用途的人工晶体,被称为“光学硅”。近期以铌酸锂薄膜(LNOI)为平台的集成光子学发展迅速,有将“光学硅”变为现实的趋势。高集成意味着高局域高光强密度,使铌酸锂晶体的光折变效应变得不容忽视。光折变效应是光致折射率变化的简称,是非线性光学的重要组成部分。本文回顾了铌酸锂晶体光折变效应的发现和机理、不同掺杂及掺杂组合对光折变效应的调控,重点介绍了铋镁双掺铌酸锂晶体的光折变性能及相关理论和实验结果,概述了铌酸锂光折变波导和孤子,及基于LNOI的集成光子学器件中的光折变效应,并对未来的研究趋势进行了展望。期待我国发挥铌酸锂光折变研究及LNOI产业化的优势,在光子学芯片的竞争中占据主导地位。     

三元同成分掺镁铌酸锂晶体的生长与抗光损伤性能研究

以三元同成分为基础配料,生长了掺杂浓度为6.5 mol;、7.5 mol;的掺镁铌酸锂晶体,并与传统的掺镁5.0mol;(Li/Nb=48.38/51.62)铌酸锂晶体作对比.光斑畸变法实验表明所生长的掺镁晶体的抗光损伤能力均达到5×105 W/cm2,与掺镁5.0mol;同成分铌酸锂晶体相近.全息法测得晶体最大折射率变化分别为4.39×10-6、4.61×10-6,而掺镁5.0mol;晶体为5.62×10-6.晶体的红外光谱和紫外-可见吸收谱显示,所生长的掺镁6.5mol;、7.5mol;晶体均已超过掺杂阈值.综上可知,采用三元同成分配比是获得高质量晶体的有效途径.     

适温离子交换掺铒铌酸锂薄膜的制备研究

本文通过制备KNO₃和Er(NO₃)₃熔融混合物,将其与铌酸锂薄膜在高温管式炉中混合进行适温热扩散,并结合退火工艺,发明了一种直接在铌酸锂薄膜上掺杂Er³⁺的方法。通过不断变换热扩散温度、掺杂试剂浓度比例和晶体切向等参数,用控制变量法探究了不同参数对适温离子交换法掺杂Er³⁺效果的影响,在热扩散和退火温度360℃及KNO₃和Er(NO₃)₃质量比25∶1的参数设置下获得了表面形貌较佳的Z切掺铒铌酸锂薄膜。通过飞行时间二次离子质谱仪并利用已知掺杂浓度的薄膜进行定标,检测了所获得的掺铒铌酸锂薄膜中的Er³⁺浓度情况,对所采用适温离子交换法的有效性进行了验证。这一方法大幅简化了铌酸锂薄膜掺杂的工艺,同时节约了成本,有助于后续在铌酸锂薄膜平台上实现分区掺杂的工作,为未来定制化铌酸锂光子集成平台的搭建提供参考。     

Investigation on photorefractive properties of doped lithium niobate

Cu:LiNbO₃ crystal and Fe:Cu:LiNbO₃ crystals were grown by the Czochralski method from congruent melt. The OH^‐ absorption spectrum of doped lithium niobate crystals was measured. The photorefractive properties of doped crystals were studied by the two‐wave coupling method. The results of the two‐wave coupling experiments showed that as the concentration of doping ions increased, the diffraction efficiency and the dynamic range enhanced, the holographic response time shortened. The recording time of Fe(0.10wt%): Cu(0.10wt%): LiNbO₃ crystal is only a tenth of that of Cu(0.05wt%): LiNbO₃ crystal. Among all samples, the dynamic range of the Fe(0.10wt%): Cu(0.10wt%): LiNbO₃ crystal was the most largest (up to 40.78). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the electro-optic effect in magnesium-doped LiNbO3 crystals

Specific features of constructing indicatory surfaces of the electro-optic effect (EOE) are described. The generalized case for the symmetry class 3m and all three possible indicatory surfaces under orthogonal experimental conditions, when the directions of light propagation and electric field are orthogonal, is considered. The EOE surfaces are constructed for magnesium-doped lithium niobate crystals. The specific features of anisotropy of these surfaces are discussed and their extreme values and corresponding angular coordinates are found. To construct the indicatory surfaces, all absolute coefficients of the linear electro-optic effect are determined by the interferometric method. The difference in the electro-optic coefficients of pure and magnesiumdoped crystals does not exceed 10%. An advantage of doped crystals is their high durability to high-power laser radiation.

     

信息时代的铌酸锂晶体:进展与展望

铌酸锂晶体具有非线性效应、电光效应、声光效应、光折变效应、压电效应与热释电效应等多种物理特性,在表面声波器件、光电器件、声光器件等方面获得广泛的应用.经历了六十多年的发展,铌酸锂晶体历久弥新,随着材料特性的不断开发,新功能、新器件、新应用层出不穷,尤其是铌酸锂单晶薄膜在薄膜滤波器、集成光电器件等领域的性能具有明显优势,...     

Angular stability of electric field‐induced effects in crystalline materials

We analyze angular bandwidths of extrema of the indicative surfaces describing spatial anisotropy of piezoelectric (PE) and electrooptic (EO) properties of doped lithium niobate (LiNbO₃:MgO) and langasite (La₃Ga₅SiO₁₄) crystals. A number of highly efficient experimental geometries are suggested, which are promising for PE and EO devices. Our data obtained with both analytical and numerical techniques characterize angular stability of those devices and, in particular, their angular aperture. We show that, besides of a maximal size of the electric field‐induced effects, ‘nondirect crystal cuts’ offer considerably higher angular stability of their characteristics, when compared with that typical for ‘direct crystal cuts’ usually employed in PE and EO devices.     

Lattice vibration and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate

Raman scattering and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate were examined. The A₁(TO) modes appear in E symmetry spectrum of the doped lithium niobate. Their intensities vary with different dopings. In the spectrum of z(yy)x geometry, the properties of the lowest-frequency E(TO) mode of the Cr-doped lithium niobate are different from those of pure, Co- and Fe-doped lithium niobate. The intensity of the A₁(TO) mode at 637cm^-1 I is decreased in doped lithium niobate compared with the pure crystal. We attribute these properties to both the photorefractive effect which is enhanced by dopants and to the different occupation of the doping ions. A light climbing effect was observed in Co- and Cr-doped lithium niobate for the first time. A higher photodamage threshold and quicker light climbing speed were found in Co- and Cr-doped lithium niobate in comparison with the light climbing effect in the Fe-doped lithium niobate. The results from the photoinduced light scattering experiments were compared with those from a Raman spectroscopic study.     

Ionic impurity transport and partitioning at the solid–liquid interface during growth of lithium niobate under an external electric field by electric current injection

Transport of ionic species in the melt and their partitioning at the solid–liquid interface during growth of lithium niobate was studied under the influence of intrinsic and external electric fields. A Mn-doped lithium niobate (Mn:LiNbO₃) single crystal was grown via the micro-pulling-down (μ-PD) method with electric current injection at the interface. Mn ions were accumulated or depleted at the interface, depending on the sign of the injected current. The electric current injection induced an interface electric field as well as a Coulomb force between the interface and Mn ions. The electric field modified the transportation of Mn ions and their partitioning into the crystal, while the Coulomb force led to adsorption or rejection of Mn ions at the interface in addition to Mn concentration change due to the electric field. Effect of the Coulomb force was often observed to be larger on Mn concentration at the interface than that of the induced electric field, and dominated the redistribution of Mn in the solid. It has been experimentally and analytically shown that Mn concentration partitioned into the crystal can be obtained by multiplying Mn concentration at the interface by a field-modified partition coefficient, k_E0, instead of the conventional equilibrium partition coefficient, k₀.     

Reduction of domain wall width in VTE treated near stoichiometric LiNbO3 crystals

LiNbO₃ is a ferroelectric crystal and grows with multi domains. Different domains are separated by boundaries which are known as domain boundaries. Domain walls for congruent and VTE (Vapor Transport Equilibration) treated near stoichiometric lithium niobate samples were visualised in different crystallographic directions using chemical etching technique. The sample is etched in the mixture of HF and HNO₃ (in 1:2 volume ratios) for 10 minutes at boiling temperature. Measured domain wall width was found approximately 15‐20 µm for congruent (CLN) and it reduces to 1‐3 µm for VTE treated near stoichiometric (SLN). Activation energies were also measured by two‐probe method and found to be increasing in stoichiometric sample. This activation energy is related to defect density in the crystals. Activation energy is higher for less defective crystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

近化学计量比铌酸锂晶体组分过冷与临界生长速率研究

本文在用双坩埚提拉法生长近化学计量比LiNbO3晶体的过程中观察到了组分过冷的实验数据,同时根据Tiller-Chalmers稳定性判据公式半定量计算了近化学计量比LiNbO3晶体临界生长速率的理论值,得到一般电阻加热双坩埚提拉法生长近化学计量比LiNbO3晶体的临界生长速率为0.1mm/h数量级.通过临界生长速率解释了一系列晶体生长的实验结果.提出了一些工艺措施来避免组分过冷,根据这些工艺获得了无包裹体的近化学计量比LiNbO3晶体.     

Micro- and nanostructures in lithium niobate single crystals doped with lanthanides

Lithium niobate single crystals doped with lanthanides (Gd, Er) and nominally pure single crystals of congruent and stoichiometric compositions have been grown under time-dependent thermal conditions. Regular growth domain microstructures and periodic nanostructures have been investigated by optical microscopy and atomic force microscopy with a step from 10 to 100 nm. Comparative investigations of the Raman spectra of lithium niobate single crystals of different compositions have been performed.     

Yb3+掺杂稀土钽铌酸盐的晶体场从头计算研究

Yb³⁺掺杂晶体材料是重要的激光材料,在超短脉冲激光、大功率激光等领域有重要应用前景,但长期以来很难通过实验拟合确定Yb3+晶体场参数,尤其是低对称体系,从头计算是解决此问题的重要途经.本文介绍了适合计算稀土离子掺杂晶体的从头计算DV-Xα方法和有效哈密顿量模型,用该方法计算了Yb³⁺掺杂M型和M'型钽铌酸盐的晶场参数和旋轨耦合参数,得到的能级结构和实验能很好地符合,并发现了Yb³⁺掺杂钽铌酸盐的晶场强度参数随稀土原子序数呈现规律变化.表明结合DV-Xα计算和有效哈密顿量方法是计算Yb³⁺掺杂低对称钽铌酸盐晶体场的有效途径,结果显示Yb3+掺杂钽铌酸盐晶体有望成为新型全固态激光工作物质.