Blackbody radiation shifts in optical atomic clocks

A review of recent theoretical calculations of blackbody radiation (BBR) shifts in optical atomic clocks is presented. We summarize previous results for monovalent ions that were obtained by a relativistic all-order single-double method, where all single and double excitations of the Dirac- Fock wave function are included to all orders of perturbation theory. A recently developed method for accurate calculations of BBR shifts in divalent atoms is then presented. This approach combines the relativistic all-order method and the configuration interaction method, which provides for accurate treatment of correlation corrections in atoms with two valence electrons. Calculations of the BBR shifts in B+, Al+, and In+ have enabled us to reduce the present fractional uncertainties in the frequencies of their clock transitions as measured at room temperature: to 4 × 10-19 for Al+ and 10-18 for B+ and In+. These uncertainties approach recent estimates of the limits of precision of currently proposed optical atomic clocks. We discuss directions of future theoretical developments for reducing clock uncertainties resulting from blackbody radiation shifts.     

Sorption of an anionic dye by uncalcined and calcined layered double hydroxides: a case study

Layered double hydroxides (LDHs) with a Mg/Al molar ratio of 2:1 were synthesized by using a co-precipitation method and their calcined products (CLDHs) were obtained by heating Mg/Al-LDHs at 500 °C. Sorption of a weak acid dye, Brilliant Blue R (BBR), by LDHs and CLDHs indicated equilibrium time required for BBR sorption by CLDHs was less than 12 h, regardless of initial concentration of BBR, whereas BBR sorption by LDHs was longer than 20 h. Sorption capacity of CLDHs was much larger than that of LDHs. Therefore, CLDHs could be used to remove anionic dyes of relatively high concentrations while LDHs may only be used to remove anionic dyes of low concentrations. Isotherms for BBR sorption by CLDHs and LDHs were well described using the Freundlich and Langmuir equations, respectively. When the initial pH of BBR solutions was lower than 8.0, the final pH of the solution after sorption was enhanced and stabilized at 10.6–10.8. The effect of initial pH (<8.0) on BBR removal was negligible, which would be environmentally important for precipitation/co-precipitation of co-existing metal cations. The effects of both Cl⁻ and SO₄²⁻ on BBR sorption by CLDHs were minimal; but the presence of CO₃²⁻ markedly reduced BBR removal. Thermal regeneration for re-use of LDHs and CLDHs after BBR sorption was feasible only within the first two cycles, after which the regenerated materials suffered from a large loss in their sorption capacities.     

La3+-Pr3+共掺杂纳米TiO2粉体的光催化性能

以钛酸四丁酯(TBT)为原料, 采用溶胶-凝胶法制备了纯TiO₂和La³⁺-Pr³⁺共掺杂复合粉体(La³⁺-Pr³⁺/TiO₂), 采用XRD、 UV-Vis和TEM等测试手段分析了在紫外光照射下, 以降解甲基橙为探针反应研究其可见光催化性能。结果显示: 所有样品均为锐钛矿相纳米TiO₂, 稀土元素镧和镨掺杂后TiO₂特征衍射峰宽化, 强度降低; 与纯TiO₂、 镧掺杂TiO₂与镨掺杂TiO₂相比, 光催化剂La³⁺-Pr³⁺共掺杂TiO₂颗粒的粒径更小, 比表面积更大, 光吸收边红移程度更显著; 与未掺杂和单一掺杂的TiO₂相比较, 共掺杂的TiO₂具有更高的可见光催化性能。当La³⁺与TiO₂和Pr³⁺与TiO₂的摩尔比分别为1.0%和0.2%时, 可见光催化性能最好。可见光催化性能的提高归因于镧和镨的协同作用。     

Sc3+和Ru4+联合取代BZN基陶瓷结构与介电性能的研究

采用传统的固相反应法制备致密的Bi_1.4Sc_0.1ZnNb_1.5-xRu_xO₇陶瓷样品, 研究Sc³⁺, Ru⁴⁺共同替代对Bi₂O₃-ZnO-Nb₂O₅陶瓷的相结构、晶体化学特性和介电性能的影响。结果表明: 当掺杂量x≤0.055 mol时, 样品保持单一的立方焦绿石结构。当掺杂量x=0.055 mol时, X射线衍射峰强度变弱, 峰形变宽。随着掺杂量的增加(0≤x≤0.04 mol), 陶瓷样品的晶格常数a和A位离子与第7个氧O′平均键长R_(A-O')逐渐减小, 结晶化学参数键价和AV(O')[A₄]增大, AV(O)[A₂B₂]减小, 48f(O)偏移量ξ增加。室温下样品的介电常数随着掺杂量的增加而减小, 介电损耗逐渐增加, 介电松弛特征减弱。低温下样品呈现明显的弛豫现象, 峰值温度T_m随着掺杂量的增加向高温方向移动。利用修正的Curie-Weiss(C-W)公式对样品ε_r-T曲线进行最小二乘法拟合, 得出样品的弛豫度γ由R0样品的1.57减小到R40样品的1.33。     

Calculations of ion-atom collisions

Calculations of the total cross section for the K-shell ionization of a titanium or chromium target by projectiles of increasing atomic number, protons, ³He⁺ and ⁶Li⁺ ions, having energies in the range 0.5–2.5 MeV/amu, are presented. The calculations are performed within the semiclassical approximation and are strongly guided by perturbed-stationary-state theory. Systematic discrepancies with corresponding experimental data are found. These discrepancies suggest that the direct Coulomb excitation of the electron is not the only physical mechanism involved in inner-shell ionization and that an electron-electron interaction, previously discussed in the literature, may play an important role. A comment is made concerning the use of distorted wave functions in perturbed-stationary-state theory in relation to the probability amplitude generated by the full Born series.     

焙烧温度对Cu-Mn/γ-Al2O3催化剂催化氧化甲苯性能的影响

采用浸渍法合成了Cu-Mn/γ-Al₂O₃催化剂, 通过XRD、BET、H₂-TPR和XPS等方法对经不同温度(300~600℃)焙烧的催化剂进行表征, 采用固定床管式反应装置考察了焙烧温度对催化剂催化氧化甲苯的影响, 并讨论活性组分、表面Cu⁺/(Cu⁺+Cu²⁺)和Mn⁴⁺/(Mn⁴⁺+Mn³⁺)摩尔比值与催化剂活性的关系。结果发现, 550℃焙烧温度的催化剂活性最好, 氧化能力最强, 其转化率为95%时对应的反应温度T₉₅(286 ℃)最低, CO₂的选择性达100%。在550℃焙烧时生成的Cu_1.4Mn_1.6O₄新相以及催化剂表面中相对含量更高的Cu⁺和Mn⁴⁺是催化剂具有高活性的主要原因。     

On the structure of the NiO–Al2O3 systems, studied by diffuse-reflectance spectroscopy

Diffuse-reflectance spectra of the NiO–Al₂O₃ systems in the 350–800 nm spectral domain are analysed. Two types of Ni²⁺complexes in γ-Al₂O₃ have been found at low concentrations (<5%): [Ni²⁺6O²⁻] and [Ni²⁺4O²⁻] with octahedral (O_h) and tetrahedral (T_d) symmetries, respectively. Coexistence of these two complexes is discussed in connection with the sample preparation and their thermal treatment.     

On the relationship between emission color and Ce concentration in garnet phosphors

It is known that the emission color of Ce³⁺ doped garnets is strongly redshifted at higher Ce³⁺ concentrations. In this report, we study the cause of this redshift in Lu₃Al₅O₁₂:Ce³⁺ (LuAG:Ce) phosphors. These changes in emission color with Ce³⁺ concentration are mainly attributed to a combination of inhomogenous broadening for Ce³⁺ in LuAG and energy transfer from high energy Ce³⁺ ions to low energy Ce³⁺ ions. Evidence for inhomogenous broadening and energy transfer is given through time resolved measurements. Potential reasons for inhomogenous broadening of Ce³⁺ in these phosphors are also discussed.     

Yb to Er energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er^{3+ 4}I_13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er³⁺ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10⁻¹⁶ and 0.45 x 10⁻¹⁶ cm³ s⁻¹, respectively. Attempts of codoping the system with Nd³⁺, Eu³⁺ and Ce³⁺ have been realised in order to increase the population of the Er^{3+ 4}I_13/2 laser emitting level. Best results are obtained with Ce³⁺ ion since in the sample containing 6 x 10²⁰ Ce³⁺/cm³, the Er^{3+ 4}I_11/2 level lifetime is divided by a factor of 3 while the Er^{3+ 4}I_13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd³⁺ or Eu³⁺ ions simultaneously decreases the Er^{3+ 4}I_11/2 and ⁴I_13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.     

稀土铁酸盐的制备及光催化性能

在600℃温度下热分解配位前驱体,制备出5种稀土铁酸盐颗粒(ReFeO₃,Re=Y³⁺、La³⁺、Sm³⁺、Gd³⁺和Ho³⁺)。采用XRD、SEM、Uv-Vis DRS以及VSM等手段对所制备产物进行物相、表面形貌、能带结构以及磁性能等进行表征。XRD表明,含Y³⁺、La³⁺和Gd³⁺的前驱体灼烧后产物为单相正交晶系的ReFeO₃,而Sm³⁺和Ho³⁺的前驱体灼烧后产物则是由ReFeO₃和微量的稀土氧化物Re2O₃两相构成的复合物。DRS结果反映,所有灼烧产物从紫外区到可见区对光都有比较强的相应,能带结构有轻微差异。VSM结果显示,所有产物均具有一定的弱铁磁性,其中HoFeO₃的磁性最强,磁参数分别为:H_c=28656 A/m,M_s=0.286 Am²/kg,M_r=0.076 Am²/kg。同时用MO作为光降解模型,研究产物的光催化活性。MO降解结果显示,所有产物对MO光降解都具有良好的催化性,其中YFeO₃展现更强的催化效果,MO在其作用下,光照4h的降解率达86%。     

Al3+/Yb3+/P5+掺杂对石英玻璃紫外透过和紫外激发荧光的影响

采用溶胶-凝胶法结合高温真空烧结工艺制备了不同浓度的Al³⁺/Yb³⁺/P⁵⁺掺杂石英玻璃。研究了P⁵⁺和Al³⁺的引入对Yb³⁺掺杂石英玻璃紫外透过和紫外激发荧光光谱, 以及Yb4d电子结合能的影响, 并初步探索了其机理。研究结果表明, Al³⁺/Yb³⁺/P⁵⁺掺杂石英玻璃在190~300 nm波段的吸收主要来源于O^2-→Yb³⁺的电荷迁移吸收, 其谱带位置和Yb4d电子结合能随Yb³⁺的第二配位元素(Al、Si、P)电负性增大向高能方向移动。真空烧结条件下, 引入Al³⁺会引发石英玻璃中Yb³⁺还原为Yb²⁺, 其典型的吸收峰位于330 nm处; 然而, 在Al³⁺/Yb³⁺共掺的基础上再引入P⁵⁺, 且P⁵⁺/Al³⁺摩尔比大于1时, 可以有效抑制Yb²⁺的形成。紫外光激发引起的近红外发光(976 nm)是电子从电荷迁移态弛豫到Yb³⁺激发态向基态跃迁的结果, 可见发光(525 nm)归因于Yb²⁺的5d→4f跃迁。本文研究结果对通过优化工艺和调整组分制备出高性能的Yb³⁺掺杂光纤具有一定的指导意义。     

可见光波段稀土激光晶体的研究进展

可见光激光在数据存储、光通讯、激光显示、激光医疗、激光打印以及科学研究等领域具有非常重要的应用价值。随着蓝光LD泵浦源的商用化, 直接泵浦稀土离子掺杂激光晶体实现可见光激光输出吸引了人们极大的研究兴趣。目前, 可见光稀土离子主要集中在Pr ³⁺、Dy ³⁺、Tb ³⁺和Sm ³⁺等。其中, Pr ³⁺的研究较多, 发光波长涵盖面较广, 发射波段覆盖蓝光、绿光、红光、橙光; Dy ³⁺和Tb ³⁺因为能够发射黄光以填补Pr ³⁺的不足也吸引了广泛的研究; 此外, Sm ³⁺和Eu ³⁺也是典型的可见波段稀土发光离子。本文综述了近几年可见波段稀土离子掺杂激光晶体的研究现状, 主要以Pr ³⁺、Dy ³⁺、Tb ³⁺和Sm ³⁺掺杂YAlO₃ (YAP)、Mg : SrAl₁₂O₁₉ (SRA)等晶体为研究对象, 总结了一套适合Pr ³⁺掺杂材料的判据, 对晶体生长、结构、热学性能、偏振光谱性能和激光性能进行了系统的研究。     

YVO4∶Eu3+,Bi3+红色荧光粉的水热合成及其荧光性能

以Y₂O₃、Eu₂O₃、Bi(NO₃)₃·H₂O、浓HNO₃、偏钒酸铵、氨水、无水乙醇和一缩二乙二醇为原料,采用聚乙烯吡咯烷酮(PVP)辅助水热法合成YVO₄: Eu³⁺, Bi³⁺纳米颗粒。使用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)和荧光光谱(FL)等手段对产品进行了表征和分析。结果表明：合成的样品为YVO₄: Eu³⁺, Bi³⁺纳米颗粒,均具有四方晶相结构,其微结构随反应溶液的的pH值变化。YVO₄: Eu³⁺, Bi³⁺纳米颗粒在619 nm处有较强的红光发射(电偶极跃迁⁵D₀→⁷F₂),在594 nm有较弱的橙光发射(磁偶极跃迁⁵D₀→⁷F₁)。随着Eu/Bi比值的增大材料的荧光先增强后减弱,在Eu/Bi比值为5时样品的红光发射最强。溶液的pH值影响YVO₄: Eu³⁺, Bi³⁺纳米晶的发光强度,其中pH值为10时的样品其红光发射最强。并探讨了YVO₄: Eu³⁺, Bi³⁺纳米晶的发光机理。     

Evaluation of the capabilities of several ions to sensitize Nd in the laser material LNA (La0.9Nd0.1MgAl11O19)

In the hexaaluminate laser material La_0.9Nd_0.1MgAl₁₁O₁₉ also known as LMA:Nd the Nd³⁺ fluorescence can be enhanced by codoping the matrix with rare-earth (REⁿ⁺) or transition metal (TM^m+) ions. A large number of potential donor ions D (D = Mn²⁺, Dy³⁺, Tb³⁺, Eu²⁺, Eu³⁺ and Ti³⁺) are studied in the hexaaluminate host. The D→Nd³⁺ energy transfer, t he, luminescent efficiency as well as the back-transfer strongly depend on the overlap of the D emission and Nd³⁺ absorption, the concentration of the two ions and their localization in the crystal host. In this paper the optical properties — absorption and emission — of the D and Nd³⁺ ions as well as the D→Nd³⁺ interactions are considered using a Forster-Dexter's approach, to compare the capabilities of the different donors in the Nd³⁺-doped hexaaluminate host. The C_DNd and R₀ parameters are estimated in each case, and the results discussed in terms of the localization of the donor ions, their absorption and emission as well as their lifetime properties.     

Investigations of the EPR parameters and substitutional sites of Ni ions in CuGaS2 and AgGaS2 ternary semiconductors

The electronic paramagnetic resonance (EPR) parameters (g factors g_//, g and zero-field splitting D) of Ni³⁺ ions at both M⁺ (M = Cu, Ag) and Ga³⁺ sites in MGaS₂ ternary semiconductors are calculated from the high-order perturbation formulas based on the two spin-orbit (SO) coupling parameter model for 3d⁷ ions in tetragonal symmetry. The calculated results suggest that Ni³⁺ ions replace the monovalent M⁺ ions in MGaS₂ crystals. This point is contrary to the previous assumption that Ni³⁺ ions substitute for the isovalent Ga³⁺ ions to attain the charge neutrality. The reasonableness of the suggestion is discussed.     

Hartree–Fock study of near-edge gap states in CaF2 with Na, Cl or Sr impurities

The energy of formation and electronic structure of Na⁺, Cl⁻ and Sr²⁺ impurity centers in CaF₂ have been computed using ab initio Hartree–Fock theory and the supercell approach. The work extends and complements recent results [Solid State Commun. 118 (2001) 569] for Mg²⁺ as a substitutional impurity in CaF₂. For Na⁺ substituting for Ca²⁺ [S(Na)], charge compensation by an F⁻ vacancy [V(F)] or by a second, interstitial Na⁺ [I(Na)] are both considered. In all cases, geometry optimization is done by relaxing the positions of nearest- and next-nearest-neighbors to minimize the total energy. After correction for electron correlation, the energies of formation increase in the order Mg²⁺2+−+ results are in agreement with previous Mott–Littleton formation energies. Ion charges, charge density maps and Mulliken bond populations are obtained to show the nature of bonding in the vicinity of the defect. Na⁺ leads to states just above the CaF₂ valence band maximum (VBM), and Na⁺ (and also Mg²⁺) produce states just below the conduction band minimum. The results are in qualitative agreement with available optical data for Na⁺ and Mg²⁺ impurity effects on CaF₂ near-edge absorption but show that gap states are important in addition to perturbed excitons. A Cl⁻ impurity yields a narrow band of states above the VBM which may significantly affect the deep-ultraviolet transmission of CaF₂. Sr²⁺ does not appear to produce states in the CaF₂ gap.     

离子交换和热处理对贵金属掺杂硅酸盐玻璃光致发光的影响

贵金属纳米颗粒-玻璃复合材料是一种重要的非线性材料。利用光致发光谱及配位场理论, 深入研究了离子交换及氢气热处理对硅酸盐玻璃中贵金属离子的引入、还原、成核及生长过程的影响, 发现延长离子交换时间有利于提高玻璃中金属离子的浓度。对于掺Ag⁺硅酸盐玻璃, 不仅存在孤立Ag⁺离子, 同时也存在Ag₂⁺团簇。H₂中热处理后, 样品中孤立Ag⁺离子浓度迅速降低, 同时出现Ag₃²⁺团簇。对于掺Cu⁺硅酸盐玻璃, 仅存在孤立Cu⁺和Cu²⁺, 没有发现Cu⁺团簇的发光峰, Cu²⁺的存在造成Cu⁺的发光强度显著降低。掺Ag⁺硅酸盐玻璃经H₂热处理后, 再经过第二次离子交换往玻璃中掺Cu⁺是十分困难的。     

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

Application of Multi-walled Carbon Nanotubes/Nafion Composite Film in Electrochemical Determination of Pb2+

In this work, insoluble multi-walled carbon nanotubes (MWNTs) was dispersed into ethanol in the presence of 1% Nafion, resulting in a stable and well-distributed MWNTs/Nafion suspension characterized by TEM and particle size analyzer. After evaporation of ethanol, a uniform MWNTs/Nafion composite film-coated glassy carbon electrode (GCE) was prepared and then characterized with SEM. Furthermore, the electrochemical behavior of Pb²⁺ at the unmodified GCE, Nafion film-modified GCE and MWNTs/Nafion film-modified GCE was investigated. It was found that the reduction peak potential shifts positively and peak current remarkably increases at the MWNTs/Nafion film-modified GCE, suggesting that MWMTs/Nafion film-modified GCE exhibits catalytic ability to electrochemical reduction of Pb²⁺. Based on this, a sensitive and convenient electrochemical method was proposed for the determination of Pb²⁺. Finally, the MWMTs/Nafion film-modified GCE was successfully used to detect Pb²⁺ in a water sample.     

Mn,Cu掺杂对ZnS∶Mn,Cu电致发光材料亮度的影响

采用水热法制备了ZnS∶Mn,Cu电致发光材料,利用透射电镜对发光材料的结构和形貌进行表征,并且探讨了Cu2+、Mn2+掺杂量和反应温度对ZnS∶Mn,Cu发光材料亮度的影响。结果显示,随着Cu2+、Mn2+掺杂量的增加,发光材料的亮度也随之增加,但对于Cu2+、Mn2+掺杂都存在最佳值,当Cu2+掺杂量0.2%,Mn2+掺杂量4%,温度150℃时,得到的电致发光材料亮度较高,粒径约10nm左右。