La3Ga5SiO14晶体的介电性质、弹性与压电性质

研究了La3Ga5SiO14晶体的介电性质、弹性和压电性质，其中弹性和压电性质是利用高频振动模式通过谐振法测定的. 关键词： 介电性质 弹性 压电性质     

Tm3+掺杂硅酸镓镧(La3Ga5SiO14)晶体的结构与光学性能研究

利用X射线粉末衍射确定了Tm3+掺杂硅酸镓镧(La3Ga5SiO14,LGS)晶体的晶体结构;运用DICVOL91程序计算了该晶体不同部位的晶胞参数;测定了Tm:LGS晶体的室温吸收谱和470 nm光激发下的发射光谱;根据Judd-Ofelt理论拟合了Tm3+的三个晶场调节参数Ωt(t=2,4,6),分别为2.694×10-20 cm2,1.842×10-20 cm2,0.030 × 10-20 cm2;计算了各个能级跃迁的谱线强度、振子强度、吸收截面等,进而计算了3H4和3F4态的自发跃迁概率、辐射寿命、荧光分支比和积分发射截面,并对结果进行了分析.     

La_3Ga_5SiO_(14)声光可调谐滤波器设计

分析了La3Ga5SiO14(简称LGS)既可以做成同向声光可调谐滤波器,又可以做成大孔径非同向声光可调谐滤波器。推导出超声波频率f和光波波长λo的调谐关系;计算出滤波器的光谱分辨率R和集光能力δiθ;光入射角iθ与衍射角θd、声入射角θa之间的关系。为LGS声光可调滤波器的实用化设计提供了充分可靠的理论依据。把LGS与TeO2声光可调滤波器的光谱分辨率和集光能力做了比较,认为LGS设计成同向声光可调谐滤波器既简便又实用。     

硅酸镓镧晶体温度、应力敏感特性及优化切向研究

从叠加偏载的运动方程出发,借助微扰理论推导了压电晶片上声表面波波速的温度、应力敏感模型,提出了应力敏感系数的概念。分析了硅酸镓镧晶体在双旋转平面内的温度和应力敏感特性,并以等高线的形式给出了理论计算结果。结合机电耦合系数及束偏向等其它特性,提出了一些具有潜在应用价值的优化切向。对欧拉角为(0,150°,22°)切向基片的温度和应力敏感特性进行了实验研究。通过对石英和硅酸镓镧两种晶体的理论计算和实验比较,验证了本文理论方法和计算结果的正确性。     

Low-temperature elastic constants and piezoelectric coefficients of langasite (La3Ga5SiO14)

A complete set of elastic constants C _ij and piezoelectric coefficients e _ij of a La₃Ga₅SiO₁₄ (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C _ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C ₄₄ and C ₁₄); (ii) monotonic elastic softening (C ₆₆); and (iii) a stiffening-to-softening transition below 150?K (C ₁₁, C ₁₂, C ₁₃ and C ₃₃). In addition, a strong correlation between C ₆₆ and the piezoelectric coefficient e ₁₁ was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A ₁ and doubly degenerated E symmetries in the point group D ₃.     

Excited state dynamics of Eu3+ in the partially disordered crystals La3Ga5SiO14 and La3Ga5.5Ta0.5O14

The spectroscopic properties of two partially disordered crystals, langasite (LGS) and langatate (LGT), doped with Eu³⁺ were investigated. The fluorescence lifetimes of the ⁵D₀ and ⁵D₁ excited levels are measured. The spectral overlapping between the luminescence from the ⁵D₀ and ⁵D₁ levels was eliminated using pulsed excitation at 532 nm and suitable delays in order to improve the precision of the calculation of the spectroscopic figures of merit R₀, R₂ (the areas of the electric-dipole transitions ⁵D₀→⁷F₀ and ⁵D₀→⁷F₂, respectively, divided by the area of the magnetic-dipole one—⁵D₀→⁷F₁). The maximum splitting of the ⁷F₁ level (ΔE) is calculated from the luminescence spectra and the B₂₀ crystal field parameter is determined. We obtain R₀(LGS)>R₀(LGT), R₂(LGS)<R₂(LGT), and ΔE(LGS)>ΔE(LGT), and we discuss these results taking into account structural data, covalency and J-mixing effects.     

Direct growth of graphene film on piezoelectric La3Ga5.5Ta0.5O14 crystal

For the first time, a few layer graphene was grown on the surface of the polar X ‐cut (110) of a piezoelectric La₃Ga_5.5Ta_0.5O₁₄ crystal by the CVD method. This polar X ‐cut is characterized by a good matching of the crystal lattice parameters of La₃Ga_5.5Ta_0.5O₁₄ and two‐dimensional graphene crystal, as well as the presence of piezoelectric fields on the surface of the substrate, which could affect the graphene growth process. Raman spectroscopy investigation has shown the ability for direct growth of graphene on the piezoelectric crystal. The NEXAFS spectroscopy studies of the film grown on the surface of the X ‐cut of an La₃Ga5_.5Ta_0.5O₁₄ crystal also confirmed that the grown film is graphene. Moreover, the NEXAFS spectra enable the conclusion that additional electron states are formed as a result of chemical bonding between the atoms of graphene and the substrate which proceeds through hybridization of the valence electron states of the substrate and graphene atoms. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

La3Ga5SiO14电光调Q的Nd:LiYF激光器研究

报道了以Nd：LiYF(Nd：LYF)为增益介质、用硅酸镓镧(La3Ga5SiO14,LGS)晶体进行电光调Q的非稳腔调Q激光器的脉冲特性。Nd：LiYF的两端按σ偏振1、053μm光的布儒斯特角切割,不需另加起偏镜．实现了单一偏振光振荡。LGS晶体电光Q开关插入损耗小(2％),抗光伤阈值高(950MW／cm^2),与DKDP相比,具有不潮解等优点。当抽运能量为120J、重复率3Hz时,单脉冲输出能量为275mJ,脉冲宽度为8ns．动静比为76％．输出能量不稳定度小于3％,偏振度大于99％,光束发散角为0．7mrad。文中还对本激光器偏振特性、非稳腔设计、LiYF导热性能和热透镜效应补偿进行了分析．对LGS电光调Q开关工作性能、工作方式以及存在的问题也进行了分析。     

Rearrangement of the Ultrasmooth Surface of La3Ga5SiO14 Crystals at Heating

The morphology and phase composition of the surface of La₃Ga₅SiO₁₄ (langasite) crystals at annealing in a temperature range 1000–1200°C have been studied using electron and atomic force microscopy. It has been shown that trigonal lanthanum oxide (La₂O₃) crystals with sizes to 3–4 μm, as well as a microstructure with sizes to 50 μm with gallium excess, with the approximate composition of 15 mol % La₂O₃, 65 mol % Ga₂O₃, and 20 mol % SiO₂ are formed on the surface of langasite crystals annealed in air at temperatures above 1100°C. Possible reasons for thermal destruction of the compound can be a significant rearrangement of the disordered crystal structure of langasite caused by the interaction with air oxygen and under the intense surface diffusion of atoms of the crystal, as well as the incongruent character of melting of the La₃Ga₅SiO₁₄ compound. The revealed thermal destruction of the surface of langasite crystals should be taken into account when using this material to fabricate piezoelectric elements for operation at high temperatures.

     

Crystal growth and optical properties of Tm:La3Ga5SiO14 single crystals

High optical quality Tm:La₃Ga₅SiO₁₄ single crystals with dopant concentration of 1 at. % Tm³⁺ ions were grown by the Czochralski method. The structure was studied by the X-ray powder diffraction method. The absorption spectrum and fluorescence spectrum of Tm³⁺:La₃Ga₅SiO₁₄ crystals were measured at room temperature. PACS 42.70.-a; 42.70.Hj; 61.10.Nz; 61.66.Fn; 78.20.-e; 78.90.+t; 81.10.-h     

Crystal growth and thermal and optical properties of La3Ga5SiO14 single crystals

We have grown an almost colorless La₃Ga₅SiO₁₄ single crystal with a dimension of 26 mm using the Czochralski technique. X-ray powder diffraction of sintered material and the single crystal were performed at room temperature. The thermal expansion coefficients along Y and Z directions have been measured to be 5×10^-6 K^{- 1} and 3.8×10^-6 K^-1, respectively. The specific heat of the crystal has been measured to be 0.90 J/gK at 453.15 K. The transmittance spectra from 200 to 800 nm were measured. PACS 61.10.N; 78.70.E; 65.40.D; 65.60; 78.20.C     

LD-pumped high repetition rate Q-switched Nd:YVO4 laser by using La3Ga5SiO14 single crystal electro-optic modulator

A diode-end-pumped electro-optic (EO) Q-switched Nd:YVO4 laser operating at repetition rate of 10 kpps (pulses per second) was reported. A block of La3Ga5SiO14 (LGS) single crystal was used as a Q-switch and the driver was a metal oxide semiconductor field effect transistor (MOS-FET) pulser of high repetition rate and high voltage. At continuous wave (CW) operation, the slope efficiency of the laser was 46%, and maximum optical-to-optical efficiency was 38.5%. Using an output coupler with transmission of 70%, a 10-kpps Q-switched pulse train with 0.4-mJ monopulse energy and 8.2-ns pulse width was achieved, the optical conversion efficiency was around 15%, and the beam quality M2 factor was less than 1.2.     

ESR spectroscopy of La2Ga5SiO14:Cr single crystals

The ESR spectrum of La₃Ga₅SiO₁₄ single crystals activated by chromium ions is investigated. It is shown that chromium ions are incorporated into the La₃Ga₅SiO₁₄ crystal lattice in the trivalent state at laoctahedric positions. Orientations of the principal magnetic axes are determined, and parameters of the spin Hamiltonian are estimated. The effect of disorder of the crystal structure of the matrix on line widths and shapes of the ESR spectrum of impurity Cr³⁺ ions is discussed. I. Franko L’vov State University, 50, Dragomilov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 942–946, November–December, 1998.     

Low-temperature thermal fixing of holograms in photorefractive La(3)Ga(5)SiO(14):Pr(3+) crystal

Thermal fixing in a La(3)Ga (5)SiO (14):Pr (3+) photorefractive crystal is demonstrated all the way down to room temperature. This, to our knowledge, is the first report of such an effect in any photorefractive material. From the temperature dependence of the process the activation energy of the carriers involved in the fixing process is measured to be E(A)=0.89 eV . Further, an effective photorefractive charge density of (1.4+/-0.2)x10(16) cm (-3) and Debye screening length of (6.8+/-0.7)x10(-6) cm is measured.     

退压式La3Ga5SiO14晶体电光调Q Nd:YAG激光器激光性能研究

通过对硅酸镓镧(LGS)晶体旋光性与电光效应的交互作用的理论研究,推导出晶体旋光性和电光效应共同作用下的光强表示式I=1-4B2(Asin 2ω-Ccos 2ω)2.利用此表示式设计计算了旋光晶体LGS尺寸为8 mm×8 mm× 25 mm电光Q开关在1064 nm波长使用时的开关电压和偏振角分别为4995 V和27.3°.将理论研究得到的结论应用于LGS晶体电光调Q的Nd:YAG晶体激光器的实验研究中,实验结果与理论计算结果基本一致.得到输出能量为361 mJ,脉冲宽度为7.8 ns的脉冲激光输出.     

Piezoelectric La3Ga5.3Ta0.5Al0.2O14 crystal: growth,crystal structure perfection,piezoelectric, and acoustic properties

A five-component crystal of lanthanum–gallium silicate group La₃Ga_5.3Ta_0.5Al_0.2O₁₄ (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. The independent piezoelectric constants d ₁₁ and d ₁₄ were measured by X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves were studied by the double-crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal.     

Optical study of erbium-doped La3Ga5.5Ta0.5O14 single crystal

Single crystals of erbium-doped La₃Ga_5.5 Ta_0.5O₁₄, grown by the Czochralski method, have been investigated using methods of optical spectroscopy. Room-temperature absorption spectra were analysed in the framework of the Judd-Ofelt theory. Radiative transition rates, radiative lifetimes and luminescence branching ratios for luminescent levels of Er³⁺ have been evaluated and compared to measured luminescence intensities and lifetimes. The laser potential associated with the ⁴I_13/2-⁴I_15/2 transition near 1.55 μm has been assessed. It has been concluded that La₃Ga_5.5 Ta_0.5,O₁₄:Er crystal is an intermediate gain laser material exhibiting strong inhomogeneous broadening of absorption bands, advantageous for optical pumping with laser diodes.     

Easy-axis kagome antiferromagnet: local-probe study of Nd3Ga5SiO14

We report a local-probe investigation of the magnetically anisotropic kagome compound Nd3Ga5SiO14. Our zero-field muon spin relaxation (muSR) results provide direct evidence of a fluctuating collective paramagnetic state down to 60 mK, supported by a wipeout of the Ga nuclear magnetic resonance (NMR) signal below 25 K. At 60 mK a dynamics crossover to a much more static state is observed by muSR in magnetic fields above 0.5 T. Accordingly, the NMR signal is recovered at low T above a threshold field, revealing a rapid temperature and field variation of the magnetic fluctuations.