Two-mode nature of the Raman spectrum of lithium niobate crystals

The ordering of the host and impurity cations in nominally pure (with different values of Li/Nbratio) and doped lithium niobate crystals is studied using Raman spectroscopy. It is shown that depending on the composition-controlled ordering of structural units of the cationic sublattice the crystal may exhibit, in the region of bridge stretching vibrations of the oxygen ions, either single-mode or two-mode behavior. The nominally pure lithium niobate crystals show, within the homogeneity region, single-mode behavior, while the crystals doped with divalent or trivalent cations show single-mode behavior at low concentrations of the dopant and two-mode behavior at higher concentrations.     

Near-diffraction-limited laser beam shaping with diamond-turned aspheric optics

We used a pair of diamond-turned CaF(2) aspheres to convert the pure TEM(00) Gaussian spatial profile output of a diode-pumped Nd:YAG laser oscillator into a super-Gaussian intensity profile with a nearly flat phase front. The resulting super-Gaussian beam was nearly diffraction limited with an M(2) of 1.75; in the near field the 5-mm diameter beam retained a nominally flat-top intensity distribution without significant diffraction peaks for an excellent working distance of more than 50cm. A 10% improvement in amplifier-energy extraction obtained by use of the reshaped beam is demonstrated.     

Temperature dependence of the spin-lattice relaxation time for quadrupole nuclei under conditions of NMR line saturation

The contributions of different mechanisms of nuclear spin-lattice relaxation are experimentally separated for ⁶⁹Ga and ⁷¹Ga nuclei in GaAs crystals (nominally pure and doped with copper and chromium), ²³Na nuclei in a nominally pure NaCl crystal, and ²⁷Al nuclei in nominally pure and lightly chromium-doped Al₂O₃ crystals in the temperature range 80–300 K. The contribution of impurities to spin-lattice relaxation is separated under the condition of additional stationary saturation of the nuclear magnetic resonance (NMR) line in magnetic and electric resonance fields. It is demonstrated that, upon suppression of the impurity mechanism of spin-lattice relaxation, the temperature dependence of the spin-lattice relaxation time T₁ for GaAs and NaCl crystals is described within the model of two-phonon Raman processes in the Debye approximation, whereas the temperature dependence of T₁ for corundum crystals deviates from the theoretical curve for relaxation due to the spin-phonon interaction.     

Bi4Ge3O12晶体及其掺杂晶体的拉曼光谱研究

利用拉曼光谱分别对Bi4 Ge3O12(BGO)晶体以及BGO:Pb(0.02 wt%),BGO:Al(0.02 wt%)进行了分析研究.测得的拉曼光谱显示,掺杂晶体对比纯的BGO晶体,在某些特征峰处,相对强度发生改变.此外,对于掺杂的晶体,部分拉曼特征峰会有偏移.因此,可以通过测定拉曼光谱来判定样品是否含有杂质.     

化学计量比LiNbO3晶体的激光显微拉曼光谱研究

对用助熔剂提拉法生长的近化学计量比LiNbO3晶体进行了激光显微拉曼光谱测试分析,与同成分LiNbO3晶体相比较,A1(TO)与E(TO)模的谱线数目、频率基本不变,验证了LiNbO3晶体属置换式固溶体的结论.738cm-1处拉曼振动峰（A1(LO)模）的相对强度随晶体中Li2O含量的增加发生了明显的变化,在两种掺杂晶体中,此振动峰已经消失.根据Li空位模型,从占位和结构上进行了分析讨论.在152和872cm-1处拉曼振动峰半高宽随晶体中Li/Nb的增大而变窄,对二者关系进行了线性拟合,利用拟合公式可根据拉曼振动峰半高宽计算晶体中的Li/Nb值. 关键词： 化学计量比 拉曼光谱 线性拟合 半高宽     

金刚石压腔结合拉曼光谱技术进行Pb掺杂对二氧化锡高压结构性能的影响研究

因稳定的分子结构和物理化学性质,近年来SnO2在光、电、磁等方面应用日益广泛。为拓宽SnO2应用范围,对高压条件下纯SnO2和Pb掺杂SnO2结构的相变行为和拉曼光谱活性振动模的变化进行了探究。实验采用水热法制备了纯SnO2和Pb掺杂量为10%的SnO2样品。扫描电子显微镜(SEM)图表明,上述制备样品由多个纳米棒从中心发散排列而成,整体成类花状。X射线衍射图谱表明,样品在常温常压下晶体结构为四方金红石型SnO2(空间群P 42)。采用Mao-Bell型金刚石压腔结合原位拉曼光谱探究了金红石型SnO2和Pb掺杂SnO2两种材料的高压相变过程。研究结果显示,两种材料加压至26 GPa过程中,纯SnO2和Pb掺杂的SnO2的活性拉曼振动模(B 1g,E g,A2g,B2g)均向高频移动。在14 GPa时,纯SnO2的E g峰分裂,563 cm-1处出现新峰,表明SnO2从常压四方金红石型结构向CaCl2型结构相变。Pb掺杂SnO2在常压拉曼谱图中出现了577 cm-1的拉曼峰。当加压至13 GPa时,B1g振动模向A g模转变,材料发生一级相变。上述对比表明Pb掺杂的SnO2具有更低的一级相变压力点13 GPa,结果归因于SnO2晶胞中Pb离子代替Sn离子,原子之间间距变小,离子大小不同造成掺杂后价态差异表面缺陷,导致SnO2结构稳定性降低,进而降低了相变压力。此外Pb掺杂SnO2在压力12 GPa时,晶体的对称性降低,577cm-1和639cm-1处特征峰宽化开始合并成包状峰,表明有部分晶体表面原子无序性程度增加,出现晶体向非晶的转变过程。继续加压至26 GPa,两种材料特征峰渐渐消失,并未观测到其他特征峰的出现。非静水压对相变压力也存在一定程度影响。非静水压条件下部分晶体更易趋向于非晶,晶界处存在较大的应力使纳米晶体在晶界处极易形成高压相成核点,导致相变发生,进而降低相变压力。本文研究不同条件下SnO2的相变行为,丰富了极端条件下SnO2的物理化学性质的多样性研究。     

化学计量比LiNbO_3晶体的激光显微拉曼光谱研究

对用助熔剂提拉法生长的近化学计量比LiNbO3晶体进行了激光显微拉曼光谱测试分析 ,与同成分LiNbO3晶体相比较 ,A1 (TO)与E(TO)模的谱线数目、频率基本不变 ,验证了LiNbO3晶体属置换式固溶体的结论 .738cm- 1 处拉曼振动峰 (A1 (LO)模 )的相对强度随晶体中Li2 O含量的增加发生了明显的变化 ,在两种掺杂晶体中 ,此振动峰已经消失 .根据Li空位模型 ,从占位和结构上进行了分析讨论 .在 15 2和 872cm- 1 处拉曼振动峰半高宽随晶体中Li Nb的增大而变窄 ,对二者关系进行了线性拟合 ,利用拟合公式可根据拉曼振动峰半高宽计算晶体中的Li Nb值 .     

Raman scattering investigation of selenomethionine replacement in protein SOUL crystals

The vibrational properties of both wild‐type and selenomethionine (SeMet)‐substituted protein SOUL crystals have been investigated here by Raman spectroscopy. Several Raman peaks observed in the spectra of methionine and SeMet were identified as specific markers. The unambiguous assignment of these peaks has been inferred by comparing the experimental Raman spectra of the pure amino acids, recorded in solid state and in aqueous solution, and the Raman intensities computed using quantum chemical calculations. Moreover, a quantitative evaluation of the relative amount of SeMet replacement in the crystals of protein SOUL labelled with SeMet has been estimated through the ratio between the Raman intensities of marker peaks. These results offer evidence of the potential of Raman microscopy as a reliable and non‐invasive tool for novel in‐depth structural investigations in biocrystallography. Copyright © 2009 John Wiley & Sons, Ltd.     

Manifestation of the specific structural features of lithium niobate single crystals of different composition in their Raman spectra

The Raman spectra of nominally pure lithium niobate single crystals of congruent, close to stoichiometric, and stoichiometric compositions and congruent lithium niobate single crystals doped with Gd³⁺, Y³⁺, and Mg²⁺ ions have been investigated. Weak lines whose widths anomalously decrease with an increase in cation sublattice disordering at a change in the single crystal composition were found for the first time. These lines may be indicative of fine ordering processes involving structural units of the cation sublattice, as a result of which this sublattice is disordered as a whole.     

Photoelectric fields in lithium niobate crystals

Photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown in the presence of 6 wt% K₂O flux (LiNbO₃ stoich. K₂O) in nominally pure single crystals of complementary composition (LiNbO₃), complementary single crystals doped with Zn²⁺, Er³⁺ at wavelength of 476, 514.5, 530 nm are defined according to parameters of photo induced light scattering indicatrix. Photo induced changes of crystals’ refractive index are defined.     

The use of photoinduced light scattering for the evaluation of photoelectric fields in Lithium Niobate Crystals

The photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown from the melt with 58.6 mol % of Li₂O (LiNbO₃ stoich), in the nominally pure single crystals of congruent composition (LiNbO₃), and in congruent single crystals doped with Cu²⁺, Zn²⁺, and Gd³⁺ are found from the parameters of the photoinduced light scattering indicatrix obtained with the use of a 60-mW He-Ne laser.     

Acoustic properties of glycine phosphite crystals with an admixture of glycine phosphate

Acoustic and dielectric anomalies in the region of the ferroelectric phase transition in crystals of glycine phosphite (GPI) with a 2 mol % admixture of glycine phosphate (GP) are studied. The acoustic anomalies were found to differ strongly from those observed in nominally pure glycine phosphite crystals. A theoretical analysis of the acoustic and dielectric properties of the crystals was carried out within the model of a pseudoproper ferroelectric phase transition. It is shown that the acoustic anomalies, as well as the temperature dependences of the dielectric constant (for various external electric fields) and pyroelectric current observed in the vicinity of the phase transition in GPI-GP crystals, can be adequately described when the macroscopic polarization present in these crystals above the phase transition temperature is taken into account. The thermodynamic-potential parameters describing electrostriction and the biquadratic relation between the polarization and strain turned out to be close to those characterizing a nominally pure GPI crystal. An irreversible phase transition was observed to occur in GPI-GP crystals at T = 240 K, i.e., above the ferroelectric phase transition temperature.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

Ybx:KY1-x(WO4)2晶体生长及振动光谱研究

采用TSSG法生长出Ybx:KY1-xW(x=0.05)和KYbW晶体,并对两者的结构和光谱性能进行了比较。工艺参数为,转速10～15r.min-1,拉速1～2mm.d-1,生长周期10～15d,降温生长速率0.05～0.1℃.h-1,降温速率20℃.h-1。XRD分析表明两者均为低温相的β-KYW结构,两种晶体的晶格常数分别为a1=1.063nm,b1=1.034nm,c1=0.755nm,β1=130.75°,Z1=4和a2=1.061nm,b2=1.029nm,c2=0.749nm,β2=130.65°,Z2=4。测试了红外及拉曼光谱,Ybx:KY1-xW(x=0.05)样品在925,891,840,777,749cm-1具有较强的红外吸收峰,是由WO4原子基团伸缩振动引起的;KYbW样品在484和437cm-1处具有较强的红外吸收峰,反映了WO4原子基团的弯曲振动。分析了晶体的振动模式,认为两种晶体有较强的拉曼活性,钨氧双桥键WOOW和单桥键WOW基团的振动在200～1000cm-1范围内,对峰值与相应的振动进行了指认。     

物质动态结构的非弹性散射研究

在静态结构的基础上，考虑原子的振动，分子键的振动、转动和振－振运动的结构称为动态结构，它是用非弹性散射方法来测定的。本文评述研究动态结构的实验方法：中子非弹性散射，非弹性X射线散射、核非弹性散射和Raman散射以及红外吸收谱。简单介绍了声子散射理论基础，继后，分三节描述了用这些方法来研究动态结构的若干结果。1）结晶物质，包括晶内，表面和界面，高纯近完整晶体中杂质引起的，多晶中、薄膜和纳米晶体中的点阵动力学研究；2）非晶物质，包括非晶固体，高聚合物，生物大分子，准晶和液体的动态结构研究；3）高温超导体的点阵动力学研究，文末给出了小结和最后评论。     

Thermoluminescence of nominally pure KTaO 3 crystals

After an exposure to ultraviolet light ( u <350 v nm) at 12 v K, weak thermoluminescence of nominally pure KTaO 3 crystals was observed within the temperature region from 13 to 65 v K for the first time. An analysis of the glow curves of integral thermoluminescence revealed five glow peaks with markedly sample-dependent intensities. Three glow peaks near 26, 31, and 58 v K at the heating rate of 0.155 v K/s correspond to thermoluminescence spectrally very similar to broad-band visible photoluminescence. The glow peaks near 26 and 31 v K were assigned to the electron release from photoinduced Ta 4+ -OH m and Ta 4+ - V O centers and the glow peak near 58 v K to the hole release from photoinduced O m centers. The glow peaks near 34 and 41 v K are connected with the structureless emission band peaking near 714 v nm at 15 v K that was observed in the emission spectra of KTaO 3 crystals for the first time.     

Ion diffusion-controlled thermally stimulated processes in X-ray irradiated halide crystals

The ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF 2 , BaF 2 , LiBaF 3 and KBr crystals were investigated above 290 v K by means of the ionic conductivity, ionic thermally stimulated depolarisation current (TSDC) and thermal bleaching techniques. Under a DC field the halide crystals store large ionic space charge. We were able to detect in CaF 2 , BaF 2 , LiBaF 3 and KBr in the extrinsic ionic conductivity region a series of the ionic defect (the interstitial anion and/or anion vacancies - in fluorides; the cation vacancies - in KBr) release stages: 3-6 wide and overlapping ionic TSDC peaks. The correlated data of the ionic TSDC and the F band thermal evidence that above 290 v K the TSR processes are initiated and controlled by the ionic defect thermal detrapping, migration and interaction with the localised electronic and ionic charges and colour centres. The ion diffusion-controlled TSR processes take place in the above halide crystals.     

Polarization analysis of the Raman spectrum of As2S3 crystals

We present the first complete series of polarized Raman spectra of orpiment crystals and the corresponding possible symmetry assignments of the phonon peaks within the layer model structure. We observe new peaks and a low frequency mode which could be a rigid layer vibration. We discuss briefly on the possible implications of some inconsistencies between the expected and the observed results.     

RNA碱基的太赫兹光谱和拉曼光谱特征研究

应用傅里叶红外光谱仪和激光拉曼光谱仪测试了RNA碱基在太赫兹波段(1～10 THz)的红外和拉曼光谱,同时结合Guassian09软件和周期性边界条件下基于能量的分块方法(PBC—GEBF),分析了RNA碱基晶体的红外和拉曼光谱特征,得到了所有特征峰位置及其对应的振动模式,且计算光谱与测试光谱一致吻合,表明碱基粉末样品为无定形晶体结构。通过对红外光谱的分析可知,在太赫兹波段,腺嘌呤和鸟嘌呤都有6个红外活性振动模式,胞嘧啶和尿嘧啶分别为6个和3个红外活性振动模式,与实验结果相比,除了鸟嘌呤6.35 THz处的弱吸收峰没能重现,4.83和5.39 THz处的吸收峰简并;胞嘧啶4.3和4.79 THz处吸收峰简并;尿嘧啶3.32和3.82 THz处的吸收峰简并外,其他吸收峰的位置和强度均被准确地模拟重现。通过对拉曼光谱的分析可知,理论和实验光谱基本一致,除了尿嘧啶3.52和4.48 THz处特征峰简并;鸟嘌呤7.26和8.03 THz,3.57,4.02,4.49,4.89和5.98 THz处特征峰简并外,其他特征峰的位置和强度均被准确的模拟重现。通过对特征峰的分析和辨认,可知在1～10 THz,RNA碱基的振动模式均来源于晶格内分子的集体振动,分子间的氢键和弱相互作用力对振动模式的贡献很大,进一步分析可知,在1～5.5 THz,其振动模式来自所有原子参与的集体振动,在5.5～10 THz,振动模式来自于部分原子参与的集体振动。此项研究对揭示RNA碱基在构成生物大分子结构、生物大分子鉴定以及太赫兹波段光谱的形成机制等方面,具有重要的理论和实际参考价值。     

广西大化墨玉的矿物学及谱学特征研究

近年来大量的墨玉在国内外玉石市场上陆续出现,广西大化墨玉是最新发现的墨玉新品种。为了探究广西大化墨玉的矿物学及谱学特征,针对产自广西大化瑶族自治县的墨玉样品进行了常规检测,以及采用Ｘ射线粉末衍射仪、激光拉曼光谱仪、傅里叶红外变换光谱仪和激光剥蚀等离子体质谱仪等现代谱学仪器测试分析,从矿物组成、拉曼光谱和红外光谱以及化学元素组成进行了研究分析。常规宝石学特征测试显示广西大化墨玉的折射率为1.64(点测),比重为3.12。偏光显微镜观察显示广西大化墨玉的主要矿物为阳起石,含量大于98%,结构为显微毛毡状结构。XRD测试明确样品主要成分为阳起石,其特征面网间距为8.498 3和3.145 9 。傅里叶红外变换光谱仪测试结果显示样品的红外光谱与透闪石理论值接近,主要的特征峰为1 078,1 026,925,765,703,659,584,485,436 cm-1,其中1 078,1 026,925 cm-1为O-Si-O和Si-O-Si的反对称伸缩振动及O-Si-O对称伸缩振动,765,703,659 cm-1为Si-O-Si对称伸缩振动,584,485,436 cm-1为Si-O弯曲振动。激光拉曼光谱测试测试结果显示样品的图谱基本集中在3 500～3 800和119～1 054 cm-1这两个区域内,样品的拉曼光谱119～1 054 cm-1的特征峰中1 055,1 029和930 cm-1为闪石类矿物特征的Si-O伸缩振动,744和671 cm-1为Si-O-Si伸缩振动,且在671 cm-1是强度最大的特征峰位,代表硅氧四面体结构单元中桥氧的对称伸缩振动;在3 800～3 500 cm-1区间为M-OH伸缩振动区域,反映了M₁和M₃位置的阳离子与结构中的OH-成键的振动信息,位于3 628,3647,3 664,3 678 cm-1,这是由于OH-伸缩振动导致。通过激光剥蚀质谱仪测试分析发现样品的主要化学成分为SiO₂(52.4%),FeO(21.95%),CaO(12.5%)和MgO(12.4%)。此外还含有少量Al₂O₃,MnO,Na₂O,P₂O₅,K₂O和TiO₂,由于样品富含Fe元素,计算Mg/(Mg+Fe)=0.504,因此大化墨玉为软玉中的阳起石玉,并由此推断大化墨玉的黑色由含铁量较高所致。