The Raman effect in crystals

A review is given of progress in the theoretical and experimental study of the Raman effect in crystals during the past ten years. Attention is given to the theory of those properties of long-wavelength lattice vibrations in both cubic and uniaxial crystals which can be studied by Raman scattering. In particular the phenomena observed in the Raman scattering from crystals which lack a centre of inversion are related to the theory. The angular variations of the scattering by any type of lattice vibration in a crystal having any symmetry can be easily calculated using a complete tabulation of the Raman tensor. Recent measurements of first-order lattice vibration spectra are listed. A discussion of Brillouin scattering is included. The relation of second-order Raman spectra to critical points in the lattice vibration density of states is discussed, and measurements of the second-order spectra of diamond and the alkali halides are reviewed. The theory and experimental results for Raman scattering by electronic levels of ions in crystals are examined, and proposals for Raman scattering by spin waves, electronic excitations across the superconductive gap and by plasmons are collected together. Finally, the prospects for applying lasers as sources for Raman spectroscopy are discussed, and progress in the new technique of stimulated Raman scattering is reviewed.     

Spontaneous Raman scattering spectra of ADP and DADP crystals in different polarization schemes

Spontaneous Raman-scattering spectra of light in ADP and DADP crystals were obtained in four polarization schemes, the widths of some Raman lines were measured. The presence of a strong and sharp Raman line corresponding to the totally symmetric vibration of the phosphate group and a strong diffuse Raman satellite corresponding to the totally symmetric vibration of the ammonium group in the spontaneous scattering spectra of both (ADP and DADP) crystals was observed. According to the theory, such lines are preferable for the stimulated Raman scattering.     

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。     

掺Nd锆石类激光晶体的Raman光谱研究

测量了Nd∶YVO4和Nd∶GdVO4两种激光晶体的高温拉曼光谱.根据空间群理论指认了测定的特征谱线,依据晶格动力学理论导出了晶体热导率与积分拉曼散射强度的关系.计算了不同方向的晶体热导率,得到了与实验符合的结果.把Nd∶GdVO4晶体的高热导率归因于授主离子的质量和半径的增大,以及由此导致的晶体场效应的显著增强. 关键词： Raman光谱 激光晶体 热导率 空间群     

Ce∶BaTiO_3晶体电光和二倍频系数的拉曼散射测量

从极性晶体晶格振动的理论出发 ,推导出正交系以上晶系的晶体的拉曼散射效率与晶体电光系数和二倍频系数的关系 :测量了 Ce∶ Ba TIO3 和 Ba Ti O3 晶体各纵、横模的偏振拉曼谱。在此基础上 ,计算出这两种晶体的电光系数γ3 3 、γ5 1 和二倍频系数 d3 3 、d1 5 。结果表明 :掺微量 Ce元素对 Ba Ti O3 晶体电光系数和二倍频系数影响不大     

Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented.In all crystals, the Raman active T2g vibration mode of CaF2 was observed, whose frequency shift and fullwidth at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice.Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U6+:CaF2crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.     

Second-order Raman scattering in MgO

We have applied our recently formulated deformable-ion model, which encompasses both the shell model and the deformation-dipole model, to compute the lattice dynamics of MgO which is in very good overall agreement with the elastic constant, dielectric constant, and neutron scattering data. We use this lattice dynamics in the second-order Raman spectra calculations where the polarizability tensor constants are fitted to the experimental spectra. Our calculated spectra agree quite well with the experimental data.     

Second-order Raman spectra of CsCl single crystals

The second-order Raman spectra of CsCl single crystals have been measured at room temperature for different Raman polarizations and crystal orientations. With the help of the calculated selection rules for a CsCl-type lattice, observed nineteen peaks and shoulders were assigned by the critical point analysis based on the neutron scattering data. By comparing the observed Raman intensities with the thermally weighted two-phonon density-of-states calculated by using a simple shell model, it has turned out that though the measured spectra are dominantly determined by the two-phonon density-of-states, the effect of the q-dependence of the polarizability cannot entirely be neglected.     

一种基于荧光材料的聚合物白光发光二极管

制备了一种基于荧光聚合物共混的单发光层聚合物白光发光二极管.器件结构为铟锡氧化物/苯磺酸掺杂聚乙烯基二氧噻吩/发光层/ 1,3,5-三(N-苯基-2-苯并咪唑-2)苯41/Ba/Al,蓝光材料芴-氟化喹喔啉共聚物(PF-BPFQ5)、绿光材料苯基取代的聚对苯乙炔(P-PPV)和红光材料聚(2-甲氧基-5-(2′-乙基己氧基)-1,4-对苯乙炔)(MEH-PPV)共混为发光层.当PF-BPFQ5,P-PPV,MEH-PPV的质量比例为100∶06∶06时,获得标准的白光,色坐标为（033 关键词： 聚合物发光二极管 白光 共混     

n-SiC拉曼散射光谱的温度特性

测量了采用离子注入法得到掺N的n-SiC晶体从100—450 K的拉曼光谱. 研究了SiC一级拉曼谱、电子拉曼散射谱及二级拉曼谱的温度效应. 实验结果表明,大部分SiC一级拉曼峰会随温度升高向低波数方向移动,但声学模红移(峰值位置向低频方向移动)的幅度较光学模小. 重掺杂4H-SiC的纵光学声子等离子体激元耦合(LOPC)模频率随温度升高表现出先蓝移(峰值位置向高频方向移动)后红移的变化趋势,表明LOPC模的温度特性不仅会受到非简谐效应的影响,还与实际已离化杂质浓度有关. 电子拉曼散射峰线宽随温度升高而增 关键词： 碳化硅 温度 纵光学声子等离子体激元耦合模 电子拉曼散射     

线性多烯分子的共振拉曼光谱

线性多烯分子是重要的光电材料,它还具有光采集、 光防护、 防癌、 抗癌功能,也是物理学、 化学理论研究的理想分子。 共振拉曼光谱是研究线性多烯分子最有力的工具。 本文总结了线性多烯分子共振拉曼光谱的特征及其与分子结构的关系,包括：电子光谱(紫外-可见吸收光谱)、 拉曼光谱的性质及与外场的关系;电子能隙对碳碳原子振动的调制作用;给出几个实验结果：温度降低、 溶剂密度增加、 溶液浓度降低等会使线性多烯分子结构有序增加,π电子能隙减小,使紫外-可见吸收光谱红移;π电子离域扩展,有效共轭长度增加,拉曼活性提高,拉曼光谱红移,拉曼截面增加。 振幅模型是研究线性多烯分子较理想的模型。     

From high resolution spectroscopy to the modeling of potential energy surfaces

Methods and recipes used to establish potential energy surfaces in condensed molecular phases are discussed. The reliability of calculations is tested by confrontation with spectroscopic measurements in crystals. Optical spectroscopy, in particular, hole burning as a line-narrowing technique, as well as high resolution inelastic neutron scattering (INS), are used to resolve tunneling level structures corresponding to large-amplitude atomic and molecular motions. Rotational tunneling of methyl groups is discussed, and new measurements by INS are presented for crystals that are proposed as suitable candidates for optical studies. Translational tunneling in benzoic acid crystals and the role of promoting modes are reviewed, and new measurements of vibrational spectra by inelastic x-ray scattering are compared with INS and Raman spectra.     

Raman scattering from 2H and 3R–NbS2

Raman scattering experiments have been carried out on 2H-NbS₂ crystals and 3R-NbS₂ crystals. The spectra obtained from both compounds have been found to contain all the Raman active modes predicted by group theory. A nearest-neighbour lattice dynamics model has also been used to analyze the spectra and qualitative agreement with the experimental results is obtained. The results are also discussed in terms of the modifications expected in the Raman spectra obtained from different polytypes of the same layered compound. Some discrepancies with previously reported results are found.     

Evolution of the 128-cm-1 Raman phonon mode with temperature in Ba(Fe1-xCox)2As 2 (x = 0.065 and 0.2)

We report electronic Raman scattering measurements on Ba(Fei_1-xCo_x)₂As₂（x = 0.065 and 0.2） single crystals with Raman shifts from 9 cm^-1 up to 600 cm^-1 in the symmetry of B_lg with respect to 1 Fe unit cell.When the crystals are cooled down,the evident quasielastic peaks of Raman spectra occur only in the crystal with x = 0.065,which is due to the contribution of orbital ordering between xz and yz Fe 3d orbitals,as we reported in another work.Here,we analyze the E_g phonon at 128 cm^-1,which has the same function form of its Raman tensors as those of xz and yz Fe 3d orbitals in these two crystals respectively.Unlike their electronic continuums,no anomalies are found in the E_g phonons of these two samples,which simply follows the expressions corresponding to the anharmonic phonon decay into acoustic phonons with the same frequencies and opposite momenta.Our results indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping and there is not any indication of coupling between charge nematicity and E_g phonon mode from our experimental results,which is consistent with the results in our previous work.     

Observation of electronic Raman scattering in metallic carbon nanotubes

We present experimental measurements of the electronic contribution to the Raman spectra of individual metallic single-walled carbon nanotubes (MSWNTs). Photoexcited carriers are inelastically scattered by a continuum of low-energy electron-hole pairs created across the graphenelike linear electronic subbands of the MSWNTs. The optical resonances in MSWNTs give rise to well-defined electronic Raman peaks. This resonant electronic Raman scattering is a unique feature of the electronic structure of these one-dimensional quasimetals.     

Applications of stimulated Raman scattering

The applications of stimulated Raman scattering reviewed in this paper include: determination of spontaneous Raman parameters and nonlinear susceptibilities by gain measurements and coherent anti-Stokes Raman spectroscopy, excitation of molecular vibrations and lattice waves and measurement of their relaxation times, generation of intense tunable light in the infrared region of the spectrum. The main results of the theory of stimulated Raman scattering relevant to the understanding of these applications are discussed.     

Raman Scattering in Three-Dimensional Photonic Crystals

The optical properties of three-dimensional photonic crystals associated with the form of reflection spectra from their surface (appearance of a forbidden gap in the energy spectrum) and with the specific features of Raman scattering are analyzed. Idealized models of the energy band structure of photonic crystals are studied. Expressions for the group velocity of photons with energy close to the forbidden gap are derived. Experimental results on the Raman scattering in photonic crystals based on artificial opal as well as in fused silica are discussed. Bands due to quantum-size effects (presence of nanoclusters in fused silica and nanoglobules forming the lattice of globular photonic crystals) were manifested in the spectra of inelastic light scattering. It is proposed to use photonic crystals for the creation of sensitive sensors of organic and inorganic substances using modern Raman techniques.     

Raman spectroscopy and polarization: Selected case studies

We show, through several selected case studies, the potential benefits that can be obtained by controlling the polarization states of the exciting and scattered radiations in a Raman scattering experiment. When coupled with polarization control, Raman spectroscopy is thus capable of providing extra information on the structural properties of the materials under investigation. The experimental examples presented in this work are taken from the area of both conventional, i.e., far-field, as well as from near-field Raman spectroscopy. They cover topics such as the stress tensor measurement in strained semiconductor structures, the vibration mode assignment in pentacene thin films and the Raman scattering tensor determination from near-field measurements on azobenzene monolayers. The basic theory necessary for modelling the far- and near-field polarized Raman responses is also given and the model efficiency is illustrated on the experimental data.     

Raman scattering for weakened bonds in the intermediate state: enhancement of low-frequency vibrations

A multimode theory of the Raman scattering in resonance with an electronic transition causing a strong weakening of atomic bonds is proposed. Simple analytical relations between the Fourier transforms of the first- and second-order Raman amplitudes and the absorption are derived. It is predicted that the Raman scattering on low-frequency vibrations will be strongly enhanced. Besides the second-order Raman scattering is also enhanced as compared to the first-order scattering. The Raman excitation profiles show a structure caused by the Airy oscillations. The shapes of the profiles of all vibrations contributing to the weakening bond are the same as a consequence of the strong mode mixing under the virtual vibronic transition.     

DL-丙氨酸晶体粉末的拉曼光谱研究

拉曼光谱可作为研究分子晶体中分子振动和晶格振动的重要手段.DL-丙氨酸晶体和L-丙氨酸晶体晶胞参数相近,结构上同属于正交晶系,但它们的空间群不同,L-丙氨酸晶体的空间群是P212121,而DL-丙氨酸晶体则是Pna21.前人的工作详细研究了L-丙氨酸晶体的拉曼光谱.文章通过对DL-丙氨酸晶体粉末的拉曼光谱研究,和相同条件下D-和L-丙氨酸晶体粉末的拉曼光谱比较,获得了有关DL-丙氨酸晶体中氢键作用和分子构象的信息.