Near‐stoichiometric LiNbO3:ZrO2 single crystal growth by micro pulling down method

Crack‐free, rod‐shaped single crystals of undoped and 0.5, 0.7 and 1.0 mol% ZrO₂‐doped LiNbO₃ with a near‐stoichiometric composition were grown by the micro‐pulling down (μ‐PD) method. The structural properties of the grown crystals were examined by powder X‐ray diffraction (XRD). Electron probe micro analysis (EPMA) of the near‐stoichiometric LiNbO₃ single crystals revealed the homogeneous incorporation of Zr ions. The change in the refractive index and IR transmission spectra of the grown crystals were examined as a function of the Zr concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical properties of near stoichiometric Ce:LiNbO3 crystals

The near sotichiometric Ce:LiNbO₃ (Ce:SLN) crystals were grown by the top seeded solution growth (TSSG) method by adding K₂O flux to Li₂O‐Nb₂O₅ melt. Their UV‐vis absorption spectra and IR spectra were measured and discussed to investigate their defect structure. The results showed that the grown crystals were near stoichiometric and Ce ions in the crystals located the Li site. Photorefractive properties of Ce:SLN crystals were studied by two‐wave coupling experiment. The results of the two‐wave coupling experiments of the crystals showed that as the CeO₂ doping concentrations increased, the diffraction efficiency increased, photoconductivity decreased and the writing time and erasure time increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved blue photorefractive properties of near‐stoichiometric LiNbO3:Mn:Fe:Zr crystal

Near‐stoichiometric LiNbO₃ single crystal tri‐doped with ZrO₂, MnO and Fe₂O₃ was grown from Li‐riched melt by Czochralski method. The defect structures and composition of these crystals were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of 3466 cm^‐1 peak in infrared spectra showed that the crystal grown from Li‐riched melt was near stoichiometric. The photorefractive properties at the wavelength of 488 nm and 633 nm were investigated with two‐beam coupling experiment, respectively. The experimental results showed that the response speed and sensitivity were enhanced significantly and the high diffraction efficiency was obtained at 488 nm wavelength. This manifested that near‐stoichiometric LiNbO₃:Mn:Fe:Zr crystal was an excellent candidate for holographic storage. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of near‐stoichiometric LiNbO3 crystals and Li2O contents determination

Two kinds of near‐stoichiometric LiNbO₃ crystals (SLN11 and SLN19) were grown by a flux pulling method from stoichiometric melt with addition of 11mol%K₂O and 19mol%K₂O, respectively. Compared with the congruent melting LiNbO₃, the ultraviolet absorption edges of two crystals shift towards shorter wavelengths, and the locations of the OH^‐ infrared absorption band have obvious change and the bandwidths become greatly narrower. From these experimental results, the Li₂O contents are determined indirectly to be about 49.6mol% for SLN11 and 49.9mol% for SLN19, respectively. The Li₂O content in SLN19 is very close to the ideal value of 50mol%. The coercive fields of two crystals were measured by the poling method at room temperature. A linear relationship between the Li₂O content and the coercive field was fitted. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Inhomogeneity of composition in near‐stoichiometric LiNbO3 single crystal grown from Li rich melt

A near‐stoichiometric LiNbO₃ single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li₂O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO₃ crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure characteristics in near‐stoichiometric In:LiNbO3 single crystals grown by K2O‐flux method

With K₂O as flux, near‐stoichiometric In:LiNbO₃ (In:SLN) crystals with different indium contents were grown by the top seed solution growth (TSSG) method. Defect structure characteristics and the replacement principle of extrinsic ions were derived from X‐ray powder diffraction, differential thermal analysis (DTA), ultraviolet‐visible (UV) absorption and infrared (IR) spectrum measurement. Further analysis indicated that the threshold concentration of In₂O₃ in near‐stoichiometric LiNbO₃ crystals were about 1.1 mol%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

化学计量比LiNbO3晶体宏观生长缺陷的观察

本文对采用双坩埚提拉法(DCCZ)生长的化学计量比LiNbO3晶体中出现的机械双晶、组分过冷、包裹体等宏观生长缺陷进行了观察和分析.结果表明机械双晶通常以{102}和{104}面族为双晶面,而不是以前文献报道的{102}和{012}面族;化学计量比LiNbO3晶体双坩埚提拉法生长与同成份晶体生长不同,前者是助熔剂生长体系,生长速度稍快或温度较小的波动就会导致组分过冷,而后者属于纯熔体生长体系,不容易产生组分过冷;包裹体是由于组分过冷生长时界面失稳夹入熔体所造成的.由于这些缺陷的存在都会严重影响单晶的获得率和质量,为此,我们通过大量实验研究后提出了可以减少和避免这些生长缺陷提高晶体质量的方法.     

Fluorescence properties of Nd3+ doped stoichiometric LiNbO3 fiber single crystals by micro‐pulling down method

Using the micro‐pulling down (μ‐PD) method, 1 and 3 mol% Nd₂O₃ doped near stoichiometric lithium niobate (LiNbO₃) single crystal fibers were grown in 1 mm diameter and 35∼40 mm length. The grown crystal fibers were free of cracks and the homogeneous distribution of Nd³⁺ ion concentrations were confirmed by the electron probe micro analysis. The changes of fluorescence spectra were measured with respect to the Nd³⁺ ion doping concentration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical Properties of Er Doped Congruent and Stoichiometric LiNbO3 Single Crystals

Erbium doped LiNbO₃ (Er:LiNbO₃) single crystal fibers were grown free of cracks along c‐axis by the micro‐pulling down (μ‐PD) method. We have investigated the up‐conversion property with the change of doped Er₂O₃ concentration and the starting melt composition. An enhancement of green upconversion according host matrix is also observed the stoichiometric LiNbO₃. And, the dependence of the green emission according to Er³⁺ concentration is analyzed. The possible application of the Er³⁺ doped stoichiometric LiNbO₃ single crystal fiber for up‐conversion based optical devices is discussed.     

K2O助溶剂提拉法和富锂提拉法生长的近化学计量比LiNbO3晶体性质的比较

分别采用K2O助溶剂提拉法和富锂提拉法生长了近化学计量比LiNbO3晶体.比较了两种方法生长的晶体紫外吸收边和红外吸收谱的差别,光谱结果表明,K2O助溶剂提拉法生长的晶体组成非常均匀,而富锂提拉法生长的晶体组成不均匀,沿晶体生长方向,Li2O含量逐渐增加.另外,两种生长方法中,籽晶表面均看到螺旋状环,分析了其产生原因.     

Zn,Co双掺杂近化学计量比LiNbO_3晶体的生长及性能

以K_2O为助熔剂,应用坩埚下降法生长出了Co~(2+) 初始浓度为0.5 mol;,以及ZnO分别为3 mol;与6 mol;的单掺与双掺杂SLN晶体(分别用SLN0, SLN3, SLN6表示).测定了晶体上下部位的吸收与发射光谱.在晶体的吸收光谱中均可观察到520 nm,549 nm,612 nm,1447 nm四个吸收峰,表明Co~(2+)处于晶体的八面体场中.ZnO的掺入明显地改变了吸收峰的相对强度.在520 nm光的激发下,观察到776 nm的荧光发射,其荧光强度的相对强弱也与ZnO的掺杂量有明显的联系.从吸收边带估算出SLN0, SLN3, SLN6晶体中Li2O的含量分别为49.06 mol;,49.28 mol;, 49.10 mol;.ZnO的掺杂量对Co~(2+)在铌酸锂晶体中的浓度分布有很大的影响作用,当ZnO的掺入量为3 mol;时,明显地抑制了Co~(2+)在LiNbO_3晶体中的掺入,当ZnO掺杂量达到6 mol;时,抑制作用减弱.本文从Zn~(2+)在LiNbO_3中随浓度变化的分凝情况以及对Co~(2+)的排斥作用解释了Co~(2+)在晶体中的分布特性以及光谱的变化情况.     

Growth and photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals grown by Czochralski method

In this paper, photorefractive properties of Mg:Ce:Cu:LiNbO₃ crystals were studied. The crystals doped with different concentration of Mg ions have been grown by the Czochralski method. Mg concentrations in grown crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP‐OE/MS). The crystal structures were analyzed by the X‐ray powder diffraction (XRD), ultraviolet‐visible (UV‐Vis) absorption spectra and infrared (IR) transmitatance spectra. The photorefractive properties of crystals were experimentally studied by using two‐beam coupling. In this experiment we determined the writing time, maximum diffraction efficiency and the erasure time of crystals samples with He‐Ne laser. The results showed that the dynamic range (M/#), sensitivity (S) and diffraction efficiency (η) were dependent on the Mg doping concentration, and the Mg(4.58mol%):Ce:Cu:LiNbO₃ crystal was the most proper holographic recording media material among the six crystals studied in the paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and light‐induced scattering of Zr‐doped near‐stoichiometric Mn:Fe:LiNbO3 crystals grown by TSSG method

Near‐stoichiometric Mn:Fe:LiNbO₃ crystals doped with various concentration of ZrO₂ were grown by top seed solution growth (TSSG) method in the air atmosphere. The Zr concentration in the crystal was determined by inductively coupled plasma optical emission spectrometer. The defect structures were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of vibration peak at 3466 cm^‐1 in infrared spectra manifested that Li/Nb ratio in crystals approached to stoichiometric proportion. The fundamental absorption edge represented continuous red‐shift which was discrepancy with congruent doped LiNbO₃ crystals showed that doping ions possessed different location mechanism. The light‐induced scattering of the doped stoichiometric LiNbO₃crystals were quantitatively scaled via incident exposure energy. The results demonstrated that Zr(2 mol%):Mn:Fe:LiNbO₃ crystal had the weakest light‐induced scattering and the mechanism related to their defect structures was discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and optical damage properties of In:Zn:LiNbO3 waveguide substrate

In:Zn:LiNbO₃ crystals doped with different indium concentrations were grown by Czochralski technique. The optical damage threshold value and ultraviolet‐visible absorption spectra of the In:Zn:LiNbO₃ crystals were measured. The In:Zn:LiNbO₃ crystals were made into optical waveguide substrates using hexanedioic acid as proton exchange agent. The optical damage resistant ability of those optical waveguide substrates was investigated by the m‐line method. The optical damage threshold values of In(2mol.%):Zn(3mol.%):LiNbO₃ crystal and optical waveguide substrate are two orders of magnitude higher than those of pure LiNbO₃. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of stoichiometric LiNbO3 nanopowder through a wet chemical method

Stoichiometric lithium niobate powder which are used as feeding material in near stoichometric LiNbO₃ crystal growth have been successfully prepared from commercial niobium hydroxide [Nb(OH)₅] and nontoxic DL‐malic acid by a wet chemical method. The synthesis temperature was pre‐determined by the results from thermogravimetric and differential thermal analysis. The structure and morphology of the as‐prepared samples were observed by using the infrared spectroscopy and the scanning electron microscopy. The X‐ray diffraction experiment showed that lithium niobate powder had an ilmenite structure, and its unit cell parameters were calculated to be a = b = 0.5140 nm, c = 1.3738 nm, and V = 0.3144 nm³. The melting point of the synthesized powder is 1239 °C and Curie temperature T_c is 1122 °C. This synthesis method would be helpful to grow the near‐stoichiometric LiNbO₃ crystal with double crucible techniques. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

近化学计量比7LiNbO3晶体的生长和基本性能

为利用中子散射技术更好地研究铌酸锂晶体的结构缺陷,以Nb2O5和同位素的7LiOH为原料,采用提拉法从58.5;的7Li熔体中成功生长了近化学计量比的同位素7LiNbO3晶体.晶体质量约为35 g,室温下晶体密度为4.634g/cm3,采用差热热重(DTA/TG)分析仪测得晶体熔点为1223℃,在室温至1250℃范围内晶体重量未发生变化.室温下晶体在500～3200 nm波段平均透过率达74;,OH-吸收峰位置在2877 nm,利用紫外吸收边法测得晶体中7Li含量为49.46;.在633 nm波长下,利用c切晶片,测得晶体的折射率为No=2.2872,ne=2.1909.     

Fe:LiNbO3单晶的坩埚下降法生长及其成分不均匀性研究

本文报道了用坩埚下降法生长Fe:LiNbO3晶体的新工艺.通过选择合适的原料配比、控制固液界面的温度梯度为20～40℃/cm及晶体生长速度0.8～1.5mm/h,生长出掺杂0.04mol;Fe2O3的无宏观缺陷LiNbO3单晶.XRD图谱和DTA曲线用来表征所得晶体,并且测定了从晶体下部到上部的紫外可见吸收光谱.结果表明:沿生长方向,晶胞参数a、c增大,熔点降低,晶体中的Fe2+浓度呈增加趋势,作者分析了造成成分不均匀分布的原因.     

Growth and characterization of La3Ga5.5Ta0.5O14 crystal

La₃Ga_5.5Ta_0.5O₁₄ (LGT) crystal was grown by using the Czochralski method. The as‐grown crystal is transparent, free from inclusions and with no cracks. Specific heat, thermal expansion, dielectric constants, transmission spectrum and optical damage threshold of LGT have been measured, and the results show general properties of LGT are similar to that of La₃Ga₅SiO₁₄ (LGS) crystal. The experiment to research the Q‐switch properties of LGT has been performed and the results show LGT possesses smaller electrooptic coefficients than that of LGS and may not be an ideal material used as a Q‐switch. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

助熔剂坩埚下降法生长近化学计量比Co:LiNbO3晶体

以K2O为助熔剂,在较大的温度梯度(90～100℃/cm)条件下进行引种和晶体生长,应用坩埚下降法成功地生长出了初始CO2+掺杂浓度为0.5mol;的近化学计量比的铌酸锂晶体.测定了该晶体的红外光谱与吸收光谱,与同成份的LiNbO3晶体相比,其紫外吸收边向短波方向移动,OH-红外吸收峰的位置发生变化.观测到520,549,612nm三个分裂的尖吸收峰以及1400nm左右为发光中心的吸收带.从吸收特性可以判断,Co离子在铌酸锂晶体中呈现+2价.比较上部与下部晶体的吸收强度,可以推测出沿着晶体生长方向Co2+离子浓度逐渐降低,Co2+离子在晶体中有效的分凝系数大于1.     

Numerical and experimental studies on crack formation in LiNbO3 single crystal

A global analysis of heat transfer was carried out in an inductively heated Czochralski (CZ) furnace which was actually used to grow LiNbO₃ single crystals, and then the temperature profiles obtained were used to calculate the three-dimensional thermal stress field in the crystal. By comparing the numerical results with the experimental ones, it was found that controlling the thermal environment in the CZ furnace so that the thermal stresses at the crystal surface might not exceed a certain value is important to realize the cracking free growth operation. In this study, this was accomplished through some modifications in the furnace design such as insertion of an after-heater into the furnace. These findings were verified by additional numerical simulations and crystal growth experiments for some growth conditions.