压力和温度对固氘掺锂体系的影响

 利用路径积分蒙特卡罗方法，研究了压力和温度变化对固氘掺锂体系的影响。结果表明，在高压条件下（0.9~2.4 GPa），锂原子掺入固体氘后，要占据五个氘分子空位形成稳定结构。温度变化不能改变这一五空位占据。固氘掺锂体系锂原子吸收谱随压力和温度的变化趋势类似于固氢掺锂体系锂原子吸收谱随压力和温度变化的趋势。但在某一固定压力和温度点，这两种吸收谱却由于氘分子和氢分子零点振动的不同有着明显的差异。随着温度或压力的增加，这两种吸收谱间的差异越来越小。     

钽酸锂、蓝宝石在高压下的光学性质从头算研究

采用量子力学从头算和赝势平面波基组以及非局域广义梯度近似(PP-GGA)方法对两种光学窗口材料(单晶LiTaO3和蓝宝石α-Al2O3)在0~250 GPa静水压力范围内的光学透明性进行了研究.结果表明,随着压力的增加蓝宝石和钽酸锂的最大吸收峰位置均向低波长区移动(蓝移).蓝宝石在0~250 GPa压力下,可见光范围内一直保持其透明性,而LiTaO3则在高压下时就变得不透明了,其原因是钽酸锂的前沿能带闭合而导致其吸收带宽随外界压力的增大变宽所致.     

钽酸锂晶体组分的OH-红外吸收光谱测定方法

研究了钽酸锂晶体Li含量(组分)的OH-红外吸收谱测定方法.利用气相输运平衡的方法制备不同组分的钽酸锂晶体样品,使用三峰结构对钽酸锂晶体的OH-吸收谱进行拟合,考虑了晶体中H 的浓度对拟合参量的影响,并发现位于3 461 cm-1的分解峰L的半高宽不受晶体中H 浓度的影响,具有很好的稳定性,非常适宜用来进行钽酸锂晶体组分的确定,最后给出了该峰的半高宽(ΓL)对组分(CLi)的依赖关系.     

Y型四能级系统中Doppler展宽对VIC相关的双光子吸收的影响

利用数值计算结果讨论了Doppler展宽对Y型四能级原子系统中真空诱导相干 性(VIC)相关的双光子吸收的影响. 研究结果表明: 1)在无Doppler展宽的情况中, 不存在VIC时, 吸收曲线具有双峰结构并产生电磁感应透明(EIT)现象, 存在VIC时吸收曲线具有单峰结构而EIT现象不再发生; 2)在有Doppler展宽的情况中, 不管是否存在VIC, EIT现象都能发生; 不存在VIC时, 不管探测场和驱动场传播方向相同还是相反, 随Doppler展宽宽度D值的增大, 吸收先增大后减小, 吸收曲线逐渐从双峰结构变为单峰结构; 存在VIC时, 若探测场和驱动场传播方向相同, 随D值的增大, 吸收先增大后减小, 吸收曲线逐渐从单峰结构变为双峰结构; 若探测场和驱动场传播方向相反, 随D值的增大, 吸收单调减小, 但吸收曲线仍保持单峰结构.     

掺铁铌酸锂晶体第一性原理研究

利用第一性原理计算方法研究铁掺杂铌酸锂晶体的电子结构和光学性质，所有计算采用广义梯度近似下的平面波超软赝势方法，得到如下结论：掺杂产生的杂质能级，主要由铁的d轨道贡献。掺杂降低了电子跃迁所需能量，同时也降低了各原子的电子轨道能量。掺杂离子在晶体中既是电子的施主又是受主。铁的掺杂使铌酸锂晶体的能量损失函数有较大的增加，对光存储的效率有一定影响。铁的掺杂使晶体的光学性质在可见光低能范围发生变化，吸收谱在可见光区域产生吸收峰，有利于晶体全息存储的应用。     

原子吸收光谱法测定铝锂合金中锂

本文研究了用原子吸收光谱法在笑气－乙炔火焰中测定铝锂合金中锂的最佳条件。其电离干扰可通过加进钾进盐来控制。应用本法测定合金中 锂的含量，获得了满意结果。     

锂原子能量的近似解

本文用屏蔽库仑势模型将锂原子的哈密顿量加以简化，然后用微扰法求解了锂原子一系列能级值，计算简洁，结果也与实验值符合得很好。     

硼酸锂系列晶体的高压拉曼散射研究

本文进行了硼酸锂系列晶体的高压拉曼散射及其压致相变的研究。对于三硼酸锂（ＬｉＢ３Ｏ５），我们发现在５．０ＧＰａ有一可逆的晶态到晶态的相变，在２７．０ＧＰａ有一不可逆的晶态到非晶态的相变。二硼酸锂（Ｌｉ２Ｂ４Ｏ７）不可逆压致非晶相变发生在３２．０ＧＰａ附近。对于一硼酸锂，我们研究了０—５５．８ＧＰａ范围内的高压拉曼光谱，只在２．０ＧＰａ发现了一个晶态到晶态的相变，但未发现不可逆压致非晶化现象。在硼酸锂系列晶体中，不可逆压致非晶化的压力随Ｌｉ２Ｏ的含量的增加而升高。硼酸锂晶体中Ｌｉ２Ｏ的含量越高，压致非晶化越不容易发生，这与熔体急冷法制备硼酸锂玻璃的规律是一致的。     

Fe, S共掺杂SnO2材料第一性原理分析

本文采用基于第一性原理的全电势线性缀加平面波(FP-LAPW)法, 计算了Fe, S两种元素共掺杂SnO₂材料的电子结构和光学性质. 结果表明: 材料仍为直接禁带半导体, 体系呈现半金属性; Fe, S共掺可以窄化带隙, 且随S浓度增加, 态密度向低能方向移动, 带隙减小; 共掺体系电荷密度重新分布, 随S浓度增加, Fe原子极化程度增强, 原子间键合能力增强. 共掺后介电函数虚部谱与光学吸收谱各峰随S浓度增加而发生红移, 光学吸收边减小.     

甲醇锂和乙醇锂拉曼光谱的密度泛函理论研究

前人研究证明在烷氧基锂(ROLi)中锂原子直接和氧原子相连而形成O-Li健,作者依此构造出甲醇锂和乙醇锂的分子构型.目前在实验和理论计算上都尚无对甲醇锂和乙醇锂分子的拉曼光谱的报道.文章用密度泛函珲论中的B3LYP混合泛函联合6-31G(d,p)基函数组进行了这两个分子的结构优化得到其平衡构型.基于此平衡构型计算出甲醇锂和乙醇锂的振动频率和拉曼光谱,对计算所得的振动频率进行了简正坐标分析,根据各频率的势能分布进行了全面的归属指认,旨在为用拉曼光谱技术研究和分析锂离子电池固体电解质膜(SEI膜)组分提供更多的理论依据.     

Pressure effects on the absorption spectra of Na doped in solid Ar

1 Introduction Impelled by the research project for the High Energy Density Matter (HEDM) ofUSA, researchers have achieved fruitful results on the energetic species in cryogenicenvironments[1]. That the chemical performance of solid hydrogen fuel can be greatlyenhanced when being doped with a small amount of light metal is confirmed both theo-retically and experimentally[2]. For understanding the mechanism, similar systems haveattracted much interest. The system of rare gas solid doped w…     

Pressure and temperature induced modification of luminescence from tetracene single crystals

Fluorescence spectra of crystalline tetracene have been recorded in the temperature range 120 to 300 K under hydrostatic pressure up to 600 MPa. From discontinuities in both emission spectra and spectral intensities it is concluded that two phase transitions occur. The room temperature phase is transformed to a low temperature phase/high pressure phase I at T^I_t (p = 0) = 182 K, the temperature coefficient being dT^I_t/dp = 0.395 K/MPa. The phase transition is induced by a decrease of the specific volume under pressure and/or upon cooling. Lack of a significant shift of the origin of the fluorescence band near T^I_t at constant pressure is an artifact resulting from the neglect of reabsorption effects. The Stokes shift is 260 cm^-1, independent of temperature and crystal modification. In accord with previous Raman data a second phase transition occurs at T^II_t (p) = 143 K, the pressure shift being dT^II_t/dp = 0.088 K/MPa.In addition, the shift of the triplet energy as a function of pressure as well as the pressure-dependence of the rate constants governing fission of a singlet exciton into a pair of triplets is discussed utilizing their magnetic field dependences.     

Measurements of high-pressure CO2 absorption near 2.0 μm and implications on tunable diode laser sensor design

A tunable diode laser (TDL) is used to measure the absorption spectra of the R46 through R54 transitions of the 20012←00001 band of CO₂ near 2.0 μm (5000 cm⁻¹) at room temperature and pressures to 10 atm (densities to 9.2 amagat). Spectra are recorded using direct absorption spectroscopy and wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) in a mixture containing 11% CO₂ in air. The direct absorption spectra are influenced by non-Lorentzian effects including finite-duration collisions which perturb far-wing absorption, and an empirical χ-function correction to the Voigt line shape is shown to greatly reduce error in the spectral model. WMS-2f spectra are shown to be at least a factor of four less-influenced by non-Lorentzian effects in this region, making this approach more resistant to errors in the far-wing line shape model and allowing a comparison between the spectral parameters of HITRAN and a new database which includes pressure-induced shift coefficients. The implications of these measurements on practical, high-pressure CO₂ sensor design are discussed.     

Direct measurements of anticrossings of the electron-nuclear energy levels in LiYF4∶Ho3+ with submillimeter EPR spectroscopy

The electron paramagnetic resonance (EPR) spectra of impurity Ho³⁺ ions in monocrystals LiYF₄∶Ho³⁺ (0.1 and 1%) with the natural abundance of⁶Li (7.42%) and⁷Li (92.58%) isotopes, and in the sample⁷LiYF₄∶Ho³⁺ (0.1%) isotopically pure in⁷Li were taken at the temperature 4.2 K in the frequency range of 165–285 GHz. Resonance transitions between crystal field sublevels (the ground non-Kramers doublet and the nearest excited singlet) of the⁵I₈ term were detected. The refined set of crystal field parameters and the effective constant of the magnetic hyperfine interaction were determined from the detailed analysis of the recorded spectra at frequencies varied by 0.05 GHz. The fine structure of EPR lines with intervals of about 300 MHz observed in the sample LiYF₄∶Ho³⁺ (0.1%) can be interpreted as a result of the isotopic disorder in the Li sublattices. Direct information about energy gaps at the anticrossing points of the electron-nuclear sublevels of the ground doublet was obtained. These gaps are induced by the hyperfine interaction that mixes doublet and singlet states and by random crystal fields. Weak EPR signals from distorted single ion and pair centers of impurity Ho³⁺ ions were resolved. From a comparison of the measured and simulated spectra, estimates of spectral parameters of the dimer centers have been obtained.     

Multispectrum analysis of CH4 in the ν4 spectral region: II. Self-broadened half widths, pressure-induced shifts, temperature dependences and line mixing

Accurate values for line positions, absolute line intensities, self-broadened half width and self-pressure-induced shift coefficients have been measured for over 400 allowed and forbidden transitions in the ν₄ band of methane (¹²CH₄). Temperature dependences of half width and pressure-induced shift coefficients were also determined for many of these transitions. The spectra used in this study were recorded at temperatures between 210 and 314 K using the National Solar Observatory's 1 m Fourier transform spectrometer at the McMath-Pierce solar telescope. The complete data set included 60 high-resolution (0.006-0.01 cm⁻¹) absorption spectra of pure methane and methane mixed with dry air. The analysis was performed using a multispectrum nonlinear least squares curve fitting technique where a number of spectra (20 or more) were fit simultaneously in spectral intervals 5-15 cm⁻¹ wide. In addition to the line broadening and shift parameters, line mixing coefficients (using the off-diagonal relaxation matrix element formalism) were determined for more than 50 A-, E-, and F-species transition pairs in J manifolds of the P- and R-branches. The measured self-broadened half width and self-shift coefficients, their temperature dependences and the line mixing parameters are compared to self-broadening results available in the literature and to air-broadened parameters determined for these transitions from the same set of spectra.     

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.     

甲醇作为压标的拉曼研究

 利用立方氧化锆压腔研究了甲醇在温度301 K、压力169.2~713.8 MPa下C—H伸缩振动ν_{2 835}的拉曼特征,实验结果表明：在试验的压力范围内甲醇稳定,其拉曼位移和压力具有很好的线性关系。加上常压下的数据,拟合后得出压力与甲醇2 835 cm^-1拉曼线频率位移的关系为：p= -3.508 9[(Δν_p)_{2 835}]²+135.17 (Δν_p)_{2 835}+54.397(0.1~713.8 MPa)。因此在实验的压力范围内甲醇作为压标非常合适。     

The Unusual Mössbauer Spectrum of Beryl

The Mössbauer spectra of several aquamarine samples have been obtained in the temperature range of 4.2–500 K. A common feature observed in all room-temperature spectra is the presence of an asymmetric Fe²⁺ doublet (ΔE _Q～2.7 mm/s, δ～1.1 mm/s), with a very broad low-velocity peak. This asymmetry is not caused by preferred orientation since the spectrum collected under the magic angle did not show any difference in the line intensities, nor is it caused by the superposition of a Fe³⁺ doublet. At 4.2 K the spectrum of a deep-blue beryl could be well fitted with three symmetrical doublets, with the major Fe²⁺ doublet accounting for 87% of the total spectral area. At 14 K the symmetry remains, but at 30 K the low-velocity peak is again broad. Surprisingly, the spectrum at 500 K also shows a broad, but symmetrical doublet, with a clear splitting of the lines indicating the presence of at least two Fe²⁺ components. The room-temperature spectrum obtained after the 500 K run shows the same features as before the heating. A meaningful fit for the room-temperature spectrum, as well as an explanation for the temperature dependence of the Mössbauer spectra, are discussed.     

Measurements of pressure-induced shifts in the 1-0 and 2-0 bands of HF and in the 2-0 bands of H35Cl and H37Cl

Fourier absorption spectra of HCl and HF measured at room temperature and low pressures were found to show evidence of pressure-induced shifts of the spectral lines at gas pressures of only 10 torr. Self-induced shifts were measured for the HF 2-0 band and for the H³⁵Cl and H³⁷ 2-0 bands. There were also measured in the same spectra shifts in the HF 2-0 band due to HCl and shifts in both HCl bands due to HF, with indications of shift oscillation due to near-resonant dipole-dipole interactions between HCl and HF. Separate measurements were made of pressure-induced shifts in the HF 1-0 and 2-0 bands and in both isotopic HCl bands, using separately argon, neon, nitrogen and carbon dioxide as the perturbing gases.