On the long-lived excited states and the spontaneous tunnel transitions in some positively charged color center systems in alkali halide crystals

A possible energy instability of some color center systems is pointed out, including an anion vacancy (α-center) in alkali halide crystals. When an optical electron passes from an F-aggregate center to an α-center, the system as a whole occupies a lower lying energy level. As an example the probability of the spontaneous radiative tunnel transition M + α → M⁺ + F in a KC1 crystal is calculated.     

Nd~(3+)/Yb~(3+)掺杂YNbO_4粉末上转换发光特性

采用高温固相法,以50Nb_2O_5-40Y2O_3-2Nd2O_3-8Yb_2O_3的量比在1 300℃下制备Nd~(3+)/Yb~(3+)掺杂YNbO_4粉末样品。运用Judd-Ofelt理论研究样品光谱特性。由吸收谱中各吸收峰面积计算得到谱线强度参数Ωλ(λ=2,4,6),进而得出理论振子强度及实验振子强度,二者均方根偏差δ_(rms)=1.618×10-7。计算了Nd~(3+)能级4F3/2→4IJ'(J'=15/2,13/2,11/2,9/2)跃迁几率、跃迁分支比和能级寿命。4F3/2→4I11/2跃迁分支比最高(56.91%),对应波长1 062 nm。且亚稳态4F3/2能级寿命较长,为1.435 2 ms,适合作为上转换中间能级。在980 nm半导体激光器激发下,观测到波长为487,541,662 nm上转换发光,分别对应于Nd~(3+)的2G9/2→4I9/2、4G7/2→4I9/2和4G7/2→4I13/2辐射跃迁。通过样品上转换发射功率与激光器工作电流进行的曲线拟合,得到吸收光子数目依次为2.06,1.99,2.15,确定3个发射峰均对应于双光子吸收。     

Weak radiative corrections to biphotonic pair annihilations

Neutral and charged current radiative corrections to e⁺e^? → γγ are computed in the Weinberg-Salam model. It is found that the charged current dominates the result and induces a ～ 1% percentage correction, neatly characterized by polarization effects. So e⁺e^? → γγ provides a clean test for weak radiative corrections.     

孤子中的再激发研究

本文在准一维紧束缚近似下,研究了孤子中的再激发。得到 , ,, , , 。其中 , 和 分别代表中性孤子、带电孤子和带电极化子, 表示链中出现的扭结。     

Compositional modulation of CuZn,CuAl and CuNi alloys

A differential reflectometer that is capable of measuring small differences in optical reflectivity or transmissivity of two specimens and therefore enhances the structure in the spectral reflectivity of materials was used to study various α-Cu-Zn, α-Cu-Al, and Cu-Ni alloys with the aim of investigating the changes in band structure as a function of composition. In Cu-Zn and Cu-Al alloys three main absorption peaks were identified that were associated with the Δ₅ → Δ₁, X₅ → X_4' and L_2' → L₁sitions. It was found that the Δ₅→ Δ₁transition increases slightly in energy with increasing Zn or Al concentration. These transitional energies are identical for both alloys in the entire α-phase region. The X₅ → X_4' and L_2' → L₁ transitions decrease in energy with increasing solute concentration. The shift in energy is significantly larger for the Cu-Al system. In Cu-Ni alloys no shift of the absorption edge around 2.2 eV was found, which is consistent with the predictions of the virtual-bound-state model.     

The mixing and decays of isoscalar mesons

The predictions of a linear mass mixing model for pseudoscalar and vector mesons, which incorporates the effects of radial excitations, are examined. Several analyses are made fitting in each case to a different experimental value of $\text{Γ(ψ →η'γ)}\text{Γ(ψ→ηγ)}$ upon which the η-η′ mixing pattern is very sensitive. Predictions for radiative transitions among the mesons and for the ratio of production amplitudes $\text{σ}\text{(π}{}^{\mathrm{?}}\text{p→η′n)}\text{σ}\text{(π}{}^{\mathrm{?}}\text{p→ηn)}$ are compared with experiments. Results indicate a preferred value of 3.1 for $\text{Γ(ψ→η′γ)}\text{Γ(ψ→ηγ)}$.     

α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料的红绿蓝色上转换发光（英文）

利用简单的水热合成法成功制备出α-TeO2∶Ho3+,Yb3+、α-TeO2∶Tm3+,Yb3+和α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料,用980 nm的近红外光作为激发光源测定了样品的室温上转换发射光谱。结果表明:样品α-TeO2∶Ho3+,Yb3+分别发射绿光(545 nm)和红光(651 nm),分别对应于Ho3+离子的5S2→5I8和5F5→5I8能级跃迁。随着Yb3+的摩尔分数从5%增加到15%,样品在545 nm处的绿光强度明显变大,发光颜色由黄光向绿光转变。样品α-TeO2∶Tm3+,Yb3+在476 nm处发射出蓝光,对应于Tm3+离子的1G4→3H6能级跃迁,两个弱红光峰(651,675 nm)分别对应于Tm3+离子的1G4→3F4和3F2→3H6能级跃迁。随着Yb3+离子浓度的提高,蓝光与红光的相对强度也在显著提高。基于可调控性蓝光、绿光和红光的产生,α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料能产生不同颜色的光,包括白光。     

On the decomposition of the transition rhombohedral phase in the Al-30 wt.% Zn alloy

The decomposition of the transition rhombohedral α′_R-phase at the temperatures between 85 and 250 °C was investigated by transmission electron microscopy and by X-ray diffraction on single crystals. Below 161 °C the direct decomposition of α′_R-phase into the equilibrium hexagonal β-phase without the formation of the transition cubic α′-phase was found. Both transformation sequences α′_R → β and α/′_R→α′ → β were observed in the temperature range from 161 to 180 °C whereas only the previously known sequence α′_R → α′ → β was detected on ageing the alloy between 180 and 250 °C. The precipitation process at the temperatures from 161 to 180 °C is characterized by the decomposition of α′_R-phase into the equilibrium β-phase prior to the formation of the transition α′-phase and by the increased rate of decomposition of α′-precipitate. The observed transformation processes are related to the variation of strains at the partially coherent interface between α′_R-phase and α-matrix with the temperature in correlation with the metastable α′_R-phase boundary. These considerations allowed to estimate the relative stabilities of precipitated phases and their activation energies of formation and thus to discuss the decomposition mechanism of α′_R-phase at various temperatures.     

Spectroscope studies of YAlO_3: (Lu~(3 )Nd~(3 ))

An increase of the Nd~(3 ) doping concentration and an enhancement of the laser induced fluorescence in the single crystal of YAlO_3: (Lu~(3 ), Nd~(3 )) have been observed and are attributed to the size compensation effect. The low temperature (4.2K) fluorescence spectra indicate that the structure of the sharp lines arising from the radiative transitions of Nd~(3 ) ions is not changed by the existence of Lu~(3 ) ions, but the emission lines are inhomogeneously more broadened. Besides, it has been observed that the fluorescence due to the radiative transition from the Stark's sublevel R_2 of the metastable level ~4F_(3/2) to the sublevels Y_1 of the manifold ~4I_(11/2) decreases with decreasing temperature and the fluorescence arising from the transitions R_1→Y_1 is relatively increased. The experimental fact is qualitatively interpreted.     

Theoretical performance of an HF chemical CW laser

A quantitative analysis of an HF cw chemical laser is presented that includes the influence of stimulated emission on the reacting medium. The numerically determined solutions encompass one-dimensional fluid mechanics, chemical kinetics, radiative de-excitation, and their mutual interaction. A comprehensive parametric study examines the effects due to changed plenum conditions, mixture ratios and cavity parameters. Best efficiency is obtained when the pumping is by the F + H₂ reaction. Pumping by the chain reaction sequence F + H₂ → HF(υ ≤ 3) + H and H + F₂ → HF(υ ≤ 6) + F results in substantially lower efficiencies due to increased HF-HF vibration-translation deactivation. Detailed discussions are presented of (1) vibration-vibration and vibration-translation energy exchange, (2) chemical efficiency, (3) mechanisms that cause lasing termination, and (4) cavity operation with a selective grating.     

Large transverse momentum phenomena in a hadronic bremsstrahlung model

We present a bremsstrahlung model which at large transverse momenta p_T leads to an inverse power law for the pion distribution in pp → π^±0 + X. The model predicts particle yields that increase with energy at fixed p_T (breaking Feynman scaling in a definite way) and provides an understanding of the excess of π⁺'s over π^?'s, and of the increase with p_T of the associated multiplicity in the direction opposite to the observed pion; it also accounts for proton to π⁺ ratios of order 1, but in a parameter-dependent way. The recently observed increase of the mean charged multiplicity in pp → p + MM with the transverse momentum of the projectile is also accounted for.     

Are the ψ′→η c γ,ψ″→η c γ decays due to the gluon admixture?

We propose a new method for estimating the radiative transitions between the excited 1^? charmonium levels and η_c. The method is based on QCD (plus the hypothesis of local duality) and makes no reference to the standard potential picture. It is argued that the decay ψ′(3.698)→η _c γ is essentially due to the gluon admixture in the Ψ′ wave function. The most naive analysis yields approximately 0.15 keV for the ψ′→η _c γ decay width, five times smaller than preliminary data. The experimental number for Γ(ψ′→η _c γ)—0.7 keV—can be reproduced only at a price of introducing a rather large ψ″(3.772)→η _c γ amplitude, Γ(ψ″→η _c γ)～1 keV. As a byproduct, we get a reliable prediction for the ρ→πγ decay rate, Γ(ρ→πγ)≈70 keV, in good agreement with a recent measurement.     

2,2′-联苯醚二甲酸和邻菲啰啉构筑的单核铽(Ⅲ)配合物:荧光性质及对Fe~(3+)的发光传感

采用水热法合成了一种新的配合物[Tb(2,2′-oba)_2(phen)_2]~-(H_3~+O)(2,2′-oba=2,2′-联苯醚二甲酸,phen=1,10-邻菲啰啉),并用X-ray单晶衍射仪测定了晶体结构。配合物是由两个邻菲啰啉和两个2,2′-联苯醚二甲酸铽离子构成的单核分子。配合物的荧光光谱在489,546,584和622nm处出现发射峰,归属为中心Tb~(3+5)D_4→7 FJ(J=6-3)跃迁产生的特征荧光。在546nm处的发射最强,对应于~5D_4→~7F_5跃迁,为绿光。探讨了不同金属阳离子对配合物的荧光效应影响。实验结果表明Fe3+对配合物具有显著的荧光猝灭作用,在生理环境pH 4.0~8.0范围内仍然适用,因此配合物可用于生命体系中的Fe~(3+)作荧光探针。     

Tm3+掺杂SiO2-Al2O3-PbF2-AlF3玻璃的光谱特性

用高温熔融法制备了不同Tm3 摩尔分数掺杂的摩尔分数比为0.3(SiO2)…0.1(Al2O3)…0.1(AlF3)…0.5(PbF2)…x(Tm2O3)(摩尔分数x=0.5%,1.0%,2.0%,3.0%)玻璃。从吸收光谱特性出发,应用Judd-Ofelt理论,计算得到了Tm3 的J-O强度参量(Ω2,Ω4,Ω6)及Tm3 各激发能级的自发辐射跃迁概率、荧光分支比以及辐射寿命等光谱参量。在808nm波长的激光二极管激发下,研究了不同Tm3 掺杂摩尔分数下玻璃在约1.47μm与约1.8μm处的荧光特性,在掺杂摩尔分数约达到2.0%时,在1.8μm处的荧光强度达最大,然后随着掺杂摩尔分数的增大,其荧光强度反而降低。作者从Tm3 的交叉弛豫与摩尔分数猝灭效应解释了这一荧光强度变化的规律,同时,根据McCumber理论计算了Tm3 跃迁3H6→3F4的吸收截面和跃迁3F4→3H6的受激发射截面。     

A measurement of the reaction e+e- →e+e-η′ and the radiative width Γη′→γγ at petra

The reaction e⁺e^- → e⁺e^-η' has been observed in the JADE experiment at PETRA, by detecting the final state π⁺π^-γ, resulting from the decay η' → γ?⁰. The cross section was measured at an average beam energy of 17.15 GeV to be σ(e⁺e^- → e⁺e^-η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ_η'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.     

970 nm抽运下Tm3+/Yb3+共掺氧氟玻璃的频率上转换发光

稀土离子掺杂的氧氟玻璃是一种新型上转换发光材料。制备了Tm^3／Yb^3＋单掺、共掺的摩尔分数为n（SiO2）-0．30,n（PbF2）-0．50,n=（Al2O3）=0．15,n（AlF3）=（0．049-x）,n（TmF3）=y,n（YbF3）=x（x=0,0．001,0．010,0．015,0．020,y=0,0．001）系统氧氟玻璃,研究了其上转换发光特性、分析了其上转换发光机理。研究发现,在970nm抽运光源激发下,Tm^3＋单掺时没有可见光上转换发射;而加入Yb^3＋后产生了强的蓝光（452nm,476nm）、红光（647nm）及近红外光（791nm）发射,分别对应如下辐射跃迁：^1D2→^3F4、^1G4→^3H6、^1G4→^3F4和^3H4→^3H6;且随着Yb^3＋离子浓度的增加上转换发光增强。在970nm光源抽运下用Yb^3＋敏化Tm^3＋可以显著提高其上转换发光强度,且随着Yb^3＋离子浓度的增加,增强了对抽运光源的吸收并提高了Yb^3＋到T^3＋”的能量转移几率,从而增强了上转换发光强度。     

掺杂三价铽离子的碱土金属钨酸盐的光谱特性研究

本文合成了一系列掺杂三价铽离子的碱土金属钨酸盐,测定了晶体的X射线粉末衍射数据及发射光谱和激发光谱.所合成的化合物均属四方晶系,I41/a空间群,晶胞多数随金属离子半径的增大而增大.研究了在这些晶体中三价铽离子5D3→7Fi和5D4→7Fi跃迁发射的激发态及其能量传递机理和浓度猝灭机制.讨论了发射光谱和激发光谱与铽离子浓度、金属离子半径及铽离子在晶体中的溶解度的关系.     

基于对氨基苯甲酸和邻菲罗啉构筑的铕(Ⅲ)配合物的荧光传感

利用水热法合成了一种新的配合物,[Eu(PABA)₃(phen)(H₂O)]·2H₂O(1)(PABA= 对氨基苯甲酸根,phen=1,10-邻菲罗啉)。该配合物为单核分子,中心离子Eu3+的配位数9,环境为{EuO₇N₂},形成了一种扭曲的单帽四方反棱柱多面体。该配合物通过氢键进一步构筑成为三维超分子结构。配合物1在紫外灯下显现为亮红色,其荧光光谱在595和618 nm处出现了2条尖锐的发射峰,分别对应于Eu3+的5D₀→7F₁和5D₀→7F₂跃迁。研究了水溶液中不同阴离子、阳离子以及溶剂对配合物1荧光的影响,实验结果表明不同阴离子、阳离子和溶剂对该配合物的荧光强度有不同程度的影响,在各自实验条件下,F-,Pb2+和硝基苯对该配合物有显著的荧光猝灭效应。基于荧光猝灭机理,该配合物可作为F-,Pb2+和硝基苯的荧光探针。     

Why quantum mechanics indeed?

Classical mechanics assumes that its laws (and specifically the second law of Newton) are independent of spatio-temporal resolutions. To see whether there is an alternative to this assumption we write the energy of a relativistic particle in a finite-difference form, e.g., ?=?₀[1-(Δx/c Δt)²]^1/2. We assume that in the limit Δt→0 the energy ε has a simple pole a/Δt. We show that quantum mechanics in its different formulations (Schrödinger, Feynman, Schwinger, Klein-Gordon, and Dirac) follows in elementary fashion from this assumption. We also rigorously prove that the classical Poisson brackets represent a coefficient in the first power of h in the expansion of the commutator in power series in h. The uncertainty relations are seen as the consequences of well-defined resolution dependence of measurements. In particular, if the simple pole in the energy dependence on Δt is located at α′ m/h, where α′ is the stringy constant, then this dependence yields the uncertainty principle of the string theory. Here α′ m/h can be interpreted as the highest physically allowed temporal resolution.     

Observation of double-Pomeron exchange in alpha-alpha collisions at the CERN intersecting storage rings

We observed the process αα→ααX in which the α′s were emitted uncorrelated in the forward direction and the charged component of the clusterX was confined to a limited portion (|η|?2) of the central region. We identified such reactions as being due to double-Pomeron exchange, for which we found a cross-section of (720±140)μb. The raw mean charged multiplicity of the clusterX was found to be 6.76±0.07 with a dispersionD=4.8. The measurements were performed at the CERN ISR at a centre-of-mass energy of \(\sqrt s = 126\) GeV. Similarities are drawn between double-Pomeron exchange in αα and inpp collisions.