Mg2+对Fe:LiNbO3晶体光折变响应时间的影响

在Fe:LiNbO₃中掺进3mol%和6mol%MgO,生长了Mg:Fe:LiNbO₃晶体.测试了Mg:Fe:LiNbO₃晶体抗光致散射能力、衍射效率、响应时间和光电导.推导响应时间与光电导之间的关系.在Fe:LiNbO₃晶体中掺进6mol%的Mg²⁺,它的抗光致散射能力比Fe:LiNbO₃晶体提高一个数量级,响应速度比Fe:LiNbO₃晶体提高四倍.     

Preparation and holographic storage properties of tri-doped Mg:Mn:Fe:LiNbO3 crystals

Doping MgO, MnO and Fe₂O₃ in LiNbO₃ crystals, tri-doped Mg:Mn:Fe:LiNbO₃ single crystals were prepared by the conventional Czochralski method. The UV-vis absorption spectra were measured and the shift mechanism of absorption edge was also investigated in this paper. In Mg:Mn:Fe:LiNbO₃ crystal, Mn and Fe locate at the deep level and the shallow level, respectively. The two-photon holographic storage is realized in Mg:Mn:Fe:LiNbO₃ crystals by using He-Ne laser as the light source and ultraviolet as the gating light. The results indicated that the recording time can be significantly reduced for introducing Mg²⁺ in the Mg:Mn:Fe:LiNbO₃ crystal.     

Mg:Fe:LiNbO3晶体的生长及光学性能研究

在Fe:LiNbO₃中掺进MgO和Fe₂O₃以提拉技术生长Mg:Fe:LiNbO₃晶体.对晶体进行极化和还原处理.测试晶体的吸收光谱,Mg:Fe:LiNbO₃晶体吸收边相对Fe:LiNbO₃晶体发生紫移.测试晶体的红外光谱,Mg:(5 mol%)Fe:LiNbO₃晶体OH^-吸收峰由Fe:LiNbO₃晶体的3482 cm^-1移到3534 cm^-1.采用锂空位模型阐述Mg:Fe:LiNbO₃晶体,吸收边和OH-吸收峰移动的机理.测试晶体的抗光致散射能力.Mg:(5 mol%)Fe:LiNbO₃晶体抗光致散射能力比Fe:LiNbO₃晶体提高一个数量级以上.测试晶体的衍射效率和响应时间.Mg:Fe:LiNbO₃晶体响应速度比Fe:LiNbO₃晶体提高四倍.     

The effect of In doping on optical properties of Fe:LiNBO3 crystals

Fe:LiNbO₃ and In:Fe:LiNbO₃ crystals were grown by Czochralski method. The absorption spectra were measured to investigate their defect structure. The photo damage resistance and photorefractive properties were measured. The photo damage resistance of the In:Fe:LiNbO₃ crystal in which the In concentration is above the threshold value is one order of magnitude higher than that of the Fe:LiNbO₃ crystal. The mechanisms of the violet shift of the absorption edge and the enhancement of the photorefractive effect of In:Fe:LiNbO₃ crystals were investigated.     

Defect structure and optical damage resistance of Hf:Fe:LiNbO3 crystals

A series of Hf:Fe:LiNbO₃ crystals were grown by the Czochralski technique with various doping concentrations of HfO₂. Their defect structures were analyzed by the UV-visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO₃ crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals enhances remarkably with the HfO₂ concentration increasing when the HfO₂ concentration is lower than its threshold concentration (4 mol%). However, when the HfO₂ concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.     

Structure and optical damage resistance of Zn:Mn:Fe:LiNbO3 crystals

The new non-volatile holographic storage materials, Zn:Mn:Fe:LiNbO₃ crystals, were prepared by Czochralski technique. Their microstructure was measured and analyzed by infrared (IR) transmission spectra. The optical damage resistance of Zn:Mn:Fe:LiNbO₃ crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of ZnO is over a threshold concentration. Its value in Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is about three orders of magnitude higher that in Mn:Fe:LiNbO₃ crystal. The photoinduced birefringence change was measured by the Sénarmont's method. It decreased with ZnO concentration increasing. The dependence of the defects on the optical damage resistance was discussed.     

Nonvolatile holographic recording in Ti, Fe Co-doped LiTaO3 crystal

Ti, Fe Co-doped LiTaO₃ (LT) crystals have been grown by the Czochralski method from the congruent melts. The absorption spectra of crystal were measured before and after ultraviolet illumination. Holograms have been recorded in doubly doped crystals with continuous-wave laser light by use of two-color method. The maximum value of refractive-index changes 7×10⁻⁵ is achieved.     

Defect structure and nonvolatile hologram storage properties in Hf:Fe:Mn:LiNbO3 crystals

A series of Hf:Fe:Mn:LiNbO₃ crystals with various levels of HfO₂ doping were grown by Czochralski technique. The infrared spectra and ultraviolet spectra were measured and discussed to investigate their structure and defects. The optical damage resistance was characterized by the transmitted beam pattern distortion method. The nonvolatile two-color holographic recording experimental results showed that the recording speed was faster with the increase of HfO₂ doping concentration and at the same time little loss of nonvolatile diffraction efficiencies could be achieved.     

Investigation of optical photorefractive properties of Zr:Fe:LiNbO3 crystals

A series of Zr:Fe:LiNbO₃ crystals with various levels of ZrO₂ doping were grown by Czochraski technique. The optical damage resistance and photorefractive properties were deeply explored. The results showed that the ability optical damage resistance increased remarkably when the concentration of ZrO₂ is over threshold concentration, but which is lower than that of traditional damage resistant additive MgO. While, the holographic storage properties can be greatly enhanced by proper level of ZrO₂ doping in Fe:LiNbO₃. In terms of ions' site occupation model, the photo-damage resistant ability enhancement and the change of the photorefractive properties were discussed.     

LiTaO3 as holographic storage material

The optical storage properties of LiTaO₃:Fe are investigated and compared with those of the isomorphous compound LiNbO₃:Fe. Absorption, photocurrent, photoconductivity and holographic measurements are reported. In the case of photovoltaic writing similar results for LiTaO₃- and LiNbO₃-crystals are obtained. However, in the case of photoconductive writing using external electric fields LiTaO₃:Fe-crystals yield much better results due to large photoconductivity values. Considering the recording sensitivity and the extremely large storage time LiTaO₃:Fe turns out to be one of the most promising materials for photorefractive storage of volume phase holograms.     

Metastable phases in HxLi1-xTaO3 waveguide layers and pure LiTaO3

The formation of high-temperature phases in low-doped H:LiTaO₃ waveguide layers in Z-cut LiTaO₃ has been observed both by refractive-index and IR-spectra measurements. This permits us to correlate the index jumps to the changes of the OH bonds in the crystal lattice. Reversible phase transitions were detected in the temperature interval T=50–200 °C over a wide range of hydrogen content including as-grown LiTaO₃. The high-temperature phases are metastable close to room temperature. This was demonstrated by tracing the time evolution of the refractive-index change. It was shown that the high-temperature phases are responsible for the long-term refractive-index instabilities in both H:LiTaO₃ waveguides and virgin LiTaO₃. Received: 7 May 2001 / Revised version: 10 August 2001 / Published online: 30 October 2001     

锂铌比对铪铁铌酸锂晶体全息存储性能的影响

以掺杂4 mol%Hf⁴⁺的LiNbO₃:Fe:Hf系列晶体（[Li]/[Nb]比变化）为研究对象,研究了系列晶体的可见吸收光谱,在632.8nm的写入光下晶体的衍射效率、灵敏度和抗光散射能力在不同[Li]/[Nb]下的变化规律.研究发现Hf⁴⁺的浓度达到阈值浓度后,随着[Li]/[Nb]比的增大,晶体的可见吸收边会发生红移,而且晶格中[Fe²⁺]/[Fe³⁺]也会增加,这就导致随着[Li]/[Nb]比的增加,样品的衍射效率逐渐减小,写入时间缩短,灵敏度增大.同时,在晶体中,随着[Li]/[Nb]的增大,陷阱中心Fe²⁺Li数量增大会使得晶体抗光散射能力减弱.     

An optical spectroscopy study of defects in lithium tantalate single crystals

The congruent, stoichiometric, and Mg doped stoichiometric LiTaO₃ single crystals have been successfully grown by the Czochralski technique. The evolution of defect structures caused by varying composition and post-growth processing has been evaluated from the optical absorption and photoluminescence measurements. Optical absorption studies showed that the UV absorption edge is very sensitive to the composition of LiTaO₃ crystals. Photoluminescence of various LiTaO₃ single crystals at room temperature was observed. The emission bands centered at 360, 430, and 530 nm were assigned to different defects, which can well show the defect information in LiTaO₃ crystals.     

Influence of post-growth treatment on the holographic storage properties of In:Fe:LiNbO3

The congruent In (3 mol%):Fe (0.03 wt%): LiNbO₃ crystal has been grown by Czochralski method in air. Some crystal samples were reduced in Li₂CO₃ powder, and others were oxidized in Nb₂O₅ powder. The defects and ions location in crystal were investigated by infrared (IR) transmission spectrum. The photorefractive properties were measured by two-wave coupling and light-induced scattering resistance experiments. In the oxidized sample, the photovoltaic effect was the dominant process during recording. However, for the as-grown sample as well as the reduced, the photorefractive effect was governed by the diffuse field and the photovoltaic field, together. In addition, the reduction treatment made the photoconductivity increase, which resulted in shorter erasure time and lower diffraction efficiency, but higher light-induced scattering resistance ability. The oxidation treatment caused the inverse effect.     

Growth and photorefractive properties of near-stoichiometric In:Fe:Cu:LiNbO3 crystals

The near-stoichiometric LiNbO₃ crystal co-doped with In₂O₃, Fe₂O₃, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH⁻ absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm⁻¹ absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO₃ crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO₃ crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO₃ crystal is a promising candidate for blue photorefractive holographic recording.     

m线法研究掺杂LiNbO3晶体波导基片的光损伤

采用m线法研究了掺杂LiNbO₃晶体波导基片的光损伤,发现抗光损伤能力依次为Mg:LiNbO₃、LiNbO₃、Fe:LiNbO₃(氧化),Fe:LiNbO₃(还原).对于同样材料,质子交换光波导的抗光损伤能力高于钛扩散光波导。     

Luminescence properties of Eu- and Mg-doped LiTaO3 obtained via the polymeric precursor method

This work reports the pure lithium tantalate (LiTaO₃), europium (III)-doped LiTaO₃ and magnesium (II)-europium (III)-doped LiTaO₃ preparation by the polymeric precursor method, using four different powered samples of Eu³⁺ ion concentrations 0.1 and 1 at%, observing their effect on the luminescent property of the material. Results indicated LiTaO₃ phase free of secondary phases at 650 °C and the photoluminescence (PL) emission spectra showed the characteristic sharp emission bands given by Eu³⁺ ions when they are excited at a wavelength of 399 nm. An increase of dopants led us to a non-homogeneous broadening and showed a slightly larger one when Mg was added. A displacement of the transition ⁵D₀→⁷F₀ to shorter wavelengths as function of Eu³⁺concentration was also noticed.     

Defect structure and optical damage resistance of Zn:Fe:LiNbO<Subscript>3</Subscript> crystals

A series of Zn:Fe:LiNbO₃ crystals were prepared by the Czochralski technique with 0.015 wt. % Fe₂O₃ content and various concentrations of ZnO. The ultraviolet-visible absorption spectra and the infrared absorption spectra of the Zn:Fe:LiNbO₃ crystals were detected in order to investigate their defect structure. Their optical damage resistance was characterized by the photoinduced birefringence change and transmission facula distortion method. The optical damage resistance of the Zn:Fe:LiNbO₃ crystals increases remarkably when the concentration of ZnO is over its threshold concentration (more than 6.0 mol. %). The effects of defects on the optical damage resistance of the Zn:Fe:LiNbO₃ crystals are discussed in detail. Received: 25 October 2002 / Revised version: 6 January 2003 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +86-451/2300-926, E-mail: zzxxhhdoctor@sina.com     

DFT - based study of electronic structures and mechanical properties of LiTaO3: ferroelectric and paraelectric phases

Abstract

By applying ab initio calculation within density functional theory (DFT), we study the structure parameters, electronic band structure, elastic coefficients, polycrystalline elastic properties, anisotropy factors and Debye temperature of ferroelectric and paraelectric phases of LiTaO₃ within the generalised gradient approximation at ambient pressure. The atomic structure in both phases is fully relaxed and the lattice constant, angle and atomic positions are well consistent with experimental values. The computed single-crystal elastic coefficients indicate that mechanical stability of LiTaO₃ in both phases is confirmed using the generalised Born criteria. The shear, bulk and Young’s modulus, Poisson’s ratio, and Vickers hardness were computed according to theoretical elastic constants by Voight–Reuss–Hill method. Several anisotropy factors and indexes are computed to illustrate mechanical anisotropy. Both phases are shown to be weakly anisotropic. The Debye temperature is estimated using the longitude and transverse elastic wave velocity of the ideal polycrystalline LiTaO₃ aggregates. We have found that LiTaO₃ in both phases has an indirect energy band gap. The differences in the electronic structure and density of states for both phases are quite small. Our results indicate that the mechanical and bonding properties of both phases are very similar. The obtained results were compared with the available experimental and theoretical values.     

强冲击压缩下LiF，Al2O3和LiTaO3单晶的透光性

在二级轻气炮上，用高速电子相机扫描照相技术和改进的Mallory实验装置，对z切LiF，Al₂O₃(蓝宝石)和LiTaO₃单晶材料的冲击透光性进行了对比测量，并用黑密度计提取出动态图像定量化的光强对比度变化曲线.结果表明，LiF单晶在102 GPa压强下能够保持长时间的初始透光性不变，与公认的LiF具有优良的高压下透明性的认识一致.LiTaO₃单晶在实验压力(139GPa)下变成基本不透明.而Al_{关键词： 2}O₃')" href="#">Al₂O₃ LiF 3')" href="#">LiTaO₃ 光学透明性