KCl:Li:Na晶体中的F_A(Ⅱ)—F_B(Ⅱ)心

采用扩散法在KCl:Li:Na晶体中形成了浓度适当、分布均匀的F心.以汞灯进行色心转型,获得了F_A(II)心和F_B(II)心.测量77K时晶体的吸收谱,观察到明显的双峰结构.在相同的温度下测得晶体的荧光谱.F_b(II)心和F_A(II)心的荧光峰分别为2.49μm和2.66μm.采用点离子模型并在离子尺度修正中计入次近邻离子的贡献,计算了KCl晶体F_A(Li)心的非微扰态,然后以微扰法计算了F_A(Li)心的能级位置.计算值与实验值比较,结果令人满意.     

液态温度下Na:KCl晶体中F_B(Ⅱ)色心激光的实验研究

介绍了掺Na的KCl晶体中F_B(Ⅱ)心在液氮温度下的稳定激光运转.Q开关Nd:YAG激光的信频输出泵浦色心晶体.激光发射波长为2.420～2.542μm.对实验结果作了讨论.     

Kcl：Pb^2＋和RbCl：Pb^2＋单晶中HD色心的喇曼研究

本文报道KCl:Pb~(2+)和RbCl:Pb~(2+)单晶在温度77K经大剂量X射线辐照后的喇曼测量结果。根据高精度的偏振喇曼数据和最近发展起来的所谓表现型分析方法,确认频移为284cm~(-1)和270cm~(-1)的信号分别为KCl:Pb~(2+)和RbCl:Pb(2+)单晶中H_D色心的C_(1h)(010):A′动力学模振动引起的非弹性散射。     

斜面上一物体平衡时的力图应怎样画?

根据斜面上一物体的平衡条件可知,力图的正确画法应如图1所示。图1虽然正确无误,但画起来很不方便,有必要将其进行合理的简化。根据力学公理:作用在刚体上任意点A的力与作用在另一点B的同样的力(大小和方向都相同)加上一个矩为r_(BA)·F_A的力偶等效,即作用在A点的力F_A所产生的效果,等于作用在B点的力F_B加上力偶[F_A,F'_B]所产生的效果。其中F_B=F_A,F'_B=-F_B,F_A和F'_B的力偶矩m_B(F_A)=r_(BA)·F_A(如图2)。     

斜面上一物体平衡时的力图应怎样画?

根据斜面上一物体的平衡条件可知,力图的正确画法应如图1所示。图1虽然正确无误,但画起来很不方便,有必要将其进行合理的简化。根据力学公理:作用在刚体上任意点A的力与作用在另一点B的同样的力(大小和方向都相同)加上一个矩为r_(BA)·F_A的力偶等效,即作用在A点的力F_A所产生的效果,等于作用在B点的力F_B加上力偶[F_A,F_B']所产生的效果。其中F_B=F_A,F_B'=-F_B,F_A和F_B'的力偶矩m_B(F_A)=r_(BA),F_A(如图2)。根据上面的公理,物体和斜面间的摩擦力f可以用作用在物体重心C上的力f_c(f_c=f)和力偶[f,f_c'(其中f_c'=-f_c)来代替而不改变力的作用效果(如图3)。     

高功率可调谐连续NaCl：（F2^＋）H色心激光器

报道了掺硫和掺氧ＮａＣｌ：（Ｆ２＾＋）Ｈ色心激光器最新实验结果。最高输出功率分别达３Ｗ和４．８Ｗ。实验比较了掺硫及掺氧（Ｆ２＾＋）Ｈ心的热光稳定性。     

BEPCⅡ中电子云不稳定性模拟研究

正电子储存环在多束团运行时有可能发生电子云不稳定性(ECI)?.本文针对北京正负电子对撞机二期工程(BEPCⅡ)的具体条件,编写发展了模拟计算程序,以不同电子云密度抑制措施下的计算结果为基础,研究了耦合束团不稳定性和单束团不稳定性,给出了电子云不稳定性增长率和阈值密度以及色品对束团尺寸增长的抑制作用,为储存环中电子云不稳定性的前沿科学研究和BEPCⅡ工程设计提供了有意义的结果.     

KCl:OH-中O2-色心实验研究

通过调制吸收光谱和电子自旋共振(ESR)谱的测量得知,在被高能射线辐照前后,KCl:OH^-中氧的成分主要以O₂^-的形式存在。O₂^-在样品中的浓度随辐照时间增加而增加,直至(OH)^-完全被辐照分解。O₂^-有相当强的稳定性。其存在与产生过程对增加F₂⁺激光色心的稳定性无直接作用。本文还根据ES 关键词：     

BEPCⅡ中电子云密度的计算研究

正电子储存环在多束团运行时有可能发生电子云不稳定性(ECI).本文针对北京正负电子对撞机二期工程(BEPCⅡ)的具体条件,区别于国外的研究编写发展了模拟计算程序,首次给出了前室型真空管道中电子云的聚集情况,定量计算了不同前室长度,不同二次电子产额作用下的电子云密度;通过模拟计算研究了在真空管道中放置清洗电极来降低电子云密度并改变密度分布以抑制不稳定性的可能性,为储存环中电子云不稳定性的前沿科学研究和BEPCⅡ工程设计提供了有意义的结果     

伽马辐照对掺镱光纤材料特性影响的研究

掺镱光纤是高功率激光器的核心材料,但在高能射线辐照后其应用性能会显著下降,因此有必要对掺镱光纤材料在辐照环境下的性能变化进行深入研究。采用改进型化学气相沉积法结合稀土螯合物掺杂制备了系列光纤预制棒及光纤,测试了光纤在不同剂量下射线辐照前后的高功率输出性能,以及光纤预制棒辐照前后的吸收光谱及镱离子荧光寿命。结果表明:小剂量辐照后掺镱光纤的高功率输出显著下降,通过预制棒吸收光谱可看出主要是因为伽马辐照后使掺镱光纤材料中Al的相关缺陷浓度增多,在可见光区域吸收损耗增加。Ce离子的掺杂通过缓减辐致铝氧空位中心(Al-OHC)色心缺陷的增加,减少Yb离子荧光寿命的下降,可在一定程度上抑制高功率掺镱光纤的辐致暗化。     

Second order optical susceptibilities in alkali halide crystals due to FA color centers

This paper presents the first calculation of the second order optical nonlinearity of the F_A color center for second harmonic generation (SHG) in KCl:Li crystals. The real and imaginary components of the nonlinear susceptibility evaluated over a wide spectral range enclosing the resonance region of the center show interesting feature. Second harmonics generation and three wave mixing processes are nonlinear optical effects based on the second order susceptibility of materials and are very effective in providing laser radiation over a wide range of wavelengths. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear susceptibility for SHG. It is found that the system shows large resonance-enhanced second order susceptibilities for color center concentration of 10²³ m⁻³. A scheme of phase matching in terms of anomalous dispersion of the centers is discussed.     

A first-principles study of the effect of charge doping on the 1D polymerization of C(60)

We study the interplay between charge doping and intermolecular distance in the polymerization of C(60) fullerene chains by means of density functional theory-based first-principles calculations. The potential energy surface analysis shows that both the equilibrium intermolecular distance of the unpolymerized system and the polymerization energy barrier are inversely proportional to the electron doping of the system. We analyze the origin of this charge-induced polymerization effect by studying the behavior of the system's wavefunctions around the Fermi level and the structural modifications of the molecules as a function of two variables: the distance between the centers of the molecules and the number of electrons added to the system.     

Absorption Spectrum Study on Colloidal Centers in KCl:NCO:K

The absorption spectrum study on metallic colloidal centers in KCl:NCO:K crystals have been performed as a function of annealing temperature in the temperature range of 500–750K. Conversion process between F-centers and colloidal centers was observed and it is found that the NCO ions play an important role in the formation and stability of aggregative centers in alkali halides.     

Positive muon behavior in KCl with and without F centers

Positive muon behavior in KCl containing F centers has been studied. The muon spin depolarization rate showed a maximum near 120 K, which was not found in pure KCl. This is probably due to the fact that free positive muons are trapped by F centers in KCl. However, the binding energy between a positive muon and an F center is not large, so that muons detrap again above 150 K.     

Yb：YAG晶体中的色心

在用引上法生长的Ｙｂ：ＹＡＧ晶体中，存在一个独特的色心，其吸收带位于３７５ｎｍ的６２５ｎｍ，随着Ｙｂ２Ｏ３掺杂浓度的增加，色心浓度增加，探讨了晶体生长过程中色心形成机理。高强γ射线辐照Ｙｂ：ＹＡＧ晶体，诱导大量色心的形成。晶体中的 对激发态Ｙｂ＾３＋离子的荧光寿命具有流淬火效应，因此，Ｙｂ：ＹＡＧ激光晶体需要经高温退火，消除色心的影响。     

Binding of MRI contrast agents to albumin: a high-field EPR study

High-field electron paramagnetic resonance (EPR) experiments to monitor binding of lipophilic Gd(III) complexes to human serum albumin (HSA) are described. It was observed that magnetic interactions between the nitroxide moiety ofn-doxyl-stearic acids bound to HSA and Gd(III) complexes resulted in broadening of nitroxide continuous-wave EPR spectra. The broadening effect can be well described by a one-parameter model of additional Lorentzian broadening At 95 GHz, continuous-wave EPR spectra from Gd(III) complexes are fully resolved from the nitroxide signal allowing for simultaneous and independent line shape analysis. Analysis of the line width broadening effects for spectra from a series ofn-doxyl-stearic acids bound to HSA indicated a progressive decrease of spin label-Gd(III) magnetic interactions along the fatty acid (FA) binding channel, consistent with binding of Gd-DOTAP complex in the vicinity of the main FA binding site. The substantial difference in spin label-metal interactions along the FA binding channel for lipophilic Gd(III) complexes with different chelates is indicative of binding to different sites. We also report measurements of dissociation constant for noncovalent binding of Gd(III) complexes to HSA on the basis of analyses of 95 GHz Gd(III) EPR line shapes.     

重离子辐照SiO2通过能量损失产生发光色心的研究

通过红外光谱和荧光发射光谱分别对600 keV、4 MeV和5 MeV Kr离子辐照的SiO2进行发光特性的研究。在低能量辐照体系中,简单色心(F2色心)的形成在损伤过程中占据主导地位,其主要诱发蓝光发射带;在高能离子辐照条件下,离子径迹上的能量密度较大,因此缺陷浓度的增大产生了一些缺陷团簇和离子径迹,形成了复杂的色心(F2+和F3+色心等)并诱发了强烈的绿光发射带和红光发射带。该实验结果与能量损失过程中统一热峰理论模型(一个综合的基于电子能损与核能损的非弹性碰撞模型和弹性碰撞模型)的模拟结果能够很好地吻合,表明在keV～MeV能区上存在电子能损过程与核能损过程的协同效应。     

Electronic structure and magnetism of Fe-doped SiC nanotubes

The electronic structure and magnetic properties of Fe-doped SiC nanotubes are investigated by using the first-principles method based on density functional theory(DFT) in the local spin density approximation(LSDA).The calculation results indicate that the SiC nanotube of Fe substitution for C exhibits antiferromagnetism while ferromagnetism features prominently when Fe substitutes Si.This is a kind of half-metal magnetic material.The formation energy calculation results show that the formation energy of ferromagnetic structure is 3.2 eV lower than that of antiferromagnetic structure.Fe atoms are more likely to replace Si atoms.Spin-orbit coupling induces electron spin polarization in the ground state.Also,the doping Fe atoms make relaxation towards the outside of the tube to some extent and larger geometric distortion occurs when Fe substitutes C,but the whole geometric structure of SiC nanotubes is not damaged due to the doping.It is revealed in the calculation of energy band structure and density of states that more dispersed distribution of energy levels is produced near the Fermi level.For Fe substitution for Si,obviously there are spin-split and intense p-d hybrid effects by Si 3p electron spins and Fe 3d electron spins localized at the exchanging interactions between magnetic transitional metal(TM) impurities.Spin electronic density results indicate that system magnetic moments are mainly generated by the unpaired 3d electrons of Fe atoms.All these results show that the transition metal doping SiC nanotube could be a potential route to fabricating the promising magnetic materials.     

ZnS掺Mn的电子结构研究

 用自旋极化的LSD-LMTO（Local-Spin-Density Linear Muffin-Tin-Orbital Method）方法，对ZnS掺入Mn发光中心的电子结构进行了大型超原胞模拟计算。在自洽收敛的条件下，先对纯ZnS调节计算参数（原子球、空球占空比），使计算的带隙E_g=3.23 eV；然后用原子球替代方式自洽计算杂质密度在E_g中的相对位置，模拟计算了在六角结构ZnS中掺入不同浓度的Mn杂质后有关的杂质能级在E_g中的相对位置。计算结果表明：（1）单个缺陷的杂质能级性质与配位场理论结果相符合，直接用杂质态密度来表示；（2）掺入杂质的浓度对杂质能级位置的影响不大，这与实验结果相一致。     

Sb、Sm共掺杂SnO2的电子结构与光学性质第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,构建了Sm、Sb及Sm和Sb共掺杂SnO₂超晶胞模型,研究了经过几何优化后的各掺杂体系的焓变值、能带结构、态密度、电荷布居、介电常数、吸收系数、反射率等光电性质.结果表明：Sm和Sb的掺杂可以有效地提升SnO₂的导电性能,且Sb和Sm共掺杂体系的电学性能最佳. Sm和Sb掺杂还可以增加SnO₂在红外波段的电子极化能力和电子跃迁概率,提升了红外反射率,且共掺杂体系的电子束缚能力最强、反射率最高.这为SnO₂基光电材料的研制提供了一定的理论依据.