MEASUREMENT AND CALCULATION OF SPONTANEOUS EMISSION BRANCHING RATIOS, RELATIVE OSCILLATOR-STRENGTHS, TRANSITION-PROBABILITIES AND LEVEL LIFETIMES FOR ATOMIC URANIUM

We propose a laser induced sensitized fluorescence spectrometry for measuring the spontaneous emission branching ratios o?the transitions from the ten levels 5f36d7s7p-7M7, 5f36d7s7p-7L6, 5f37s27p-5K6, 5f26d27s2 - 5L7, 5f46d7s - 7L6, (17,070cm-1)-5L6, 5f26d27s2-5K6, 6d7s7p-7L5, 5f36d7s7p-7K5 and 5f26d27s2-5I5 to the ground state of atomic uranium (UI) for the first time. Their relative oscillator strengths have been measured by means of hollow cathode discharge (HCD) emission spectrometry. The radiative...

Radiative transition in delta-doped GaAs superlattices

Radiative transition in delta-doped GaAs superlattices with a weak coupling was investigted at low temperature, The experimental results show that the transitions from both electron ground state and excited state to hole state have been observed, Based on the effective mass approximation theory, the structures of energy band and photoluminescence spectra for the samples used were calculated. Comparing the experiment with theory, a good agreement was abtained.

Nd3+螯合物的含氢有机溶液光谱性能研究

Tris-thenoyltrifluroacetonate of Nd3+ has been prepared and dissolved in DMF solation with very high concentration, and the contained hydrogen has not been substituted by deuterium. The absorption spectrum, emission spectrum, and fluorescence lifetime of the solution were measured. Very obvious characteristic fluorescence peaks were observed at 898 and 1058 nm. Based on Judd-Ofelt theory, three intensity parameters were obtained: Omega(2) = 4.9 x 10(-20) cm(2), Omega(4) = 5.1 x 10(-20) cm(2) and Omega(6) = 2.5 x 10(-20) cm(2). Line strengths S-cal, oscillator strengths f(cal), radiative transition probabilities A(ed), radiative lifetimes tau(r) and branch ratios beta were calculated too. The measured lifetime tau of 1058 nm peak is 460 mu s, and that of 898 nm 505 mu s. Comparison between theoretically computed radiative lifetime tau(r)(682 mu s) and the measured lifetime indicates that the non-radiative transition probability of the solution is very low and the fluorescence quantum efficiency very high. High values of three intensity parameters prove the high asymmetric surroundings of Nd3+, which is important for Nd3+ to absorb the excitation energy. Spectropic quality factor Omega(4)/Omega(6) > 1 makes radiation at 898 nm stronger than at 1058 nm.

The luminescence of Eu3+ ion in Ca2Al2SiO7

Ca2Al2SiO7:Eu3+ was prepared by the sol-gel method. Through the emission spectrum of Eu3+ ion, the fluorescence parameters such as Omega(i) (i = 2,4) and radiative transition probabilities of D-5(0)-F-7(j) were calculated. The Pb2+ ion with bigger radius has an effect on the fluorescence spectra of Eu3+ which can be explained by the structure of the matrix. Simultaneously, the energy transfers between mercury-like ions (Pb2+ and Bi3+) and Eu3+ ion were observed. The D-5(4) and D-5(2) energy levels of Eu3+ are the resonance ones for Pb2+ ion.

Theoretical investigation of LaC2 and LaC2+ clusters

LaC2 (with doublet and quartet states) and LaC2+ (with singlet and triplet states) cluster have been studied by using the B3LYP (Becke three-parameter/Lee-Yang-Parr) density functional method and the HF (Hartree-Fock) method with LANLIDZ basis set. For each cluster, four possible isomers in C-2v, C-s, C-proportional to v and D-proportional to h symmetries have been investigated. The results indicate that structures in C-s symmetry are local minima in all cases and, in most cases (particularly for high spin states), our initial guess in C-s symmetry converges to structures in C-2v symmetry. For the isomers in C-2v, C-proportional to v and D-proportional to h symmetries, local minima were found to be dependent on the method and spin state. The two clusters may also exist as linear chains. The ordering of the binding energies for the isomers in all spin states is C-s similar to C-2v < C-proportional to v < D-proportional to h. The ionization potential of LaC2 is reported as well. (C) 1998 Elsevier Science B.V.

Theoretical investigation of LaC3n+ (n = 0, 1, 2) clusters by density functional theory

LaC3n+ (n = 0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional method. The basis set is Dunning/ Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C-2 upsilon symmetry, the other two are Linear chains with C-infinity upsilon symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC3+, doublet and quartet for LaC3 and LaC32+, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C-2 upsilon symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored. (C) 1998 John Wiley & Sons, Inc.

Atomic Structures and Radiative Properties of He-like Ions in Debye Plasmas

A detailed investigation of plasma screening effects on atomic structure and transition properties are presented for He-like ions embedded in dense plasma environment. Multi-configuration Dirac-Fock calculations were carried out for these ions by considering a Debye-Huckel potential. A large-scale relativistic configuration-interaction method is adopted to calculate transition energies and transition probabilities and to allow for a systematic improvement of the calculations. Comparison of the presently calculated results with others, when available, is made.

Infrared to visible upconversion fluorescence in Yb,Tm : YAG single crystal

Absorption spectrum from 400 to 2000 run and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb3+ and 4 at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition (1)G(4) -> H-3(6), the emission band around 646 nm corresponds to the transition (1)G(4) -> F-3(4) of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of (1)G(4) level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions (1)G(4) -> H-3(6) in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light Output. (c) 2006 Elsevier B.V. All rights reserved.

Two-electron-one-photon M1 and E2 transitions between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92

Two-electron-one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core-valence and core-core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.

在激波波面中氧分子的非平衡离解

对强激波作用下双原子分子振动与离解耦合的非平衡离解过程进行了理论计算.本工作的特点是将计算起点建立在分子基本参数上,采用主方程理论处理振动与离解的耦合,振动跃迁几率用SSH理论计算,在离解限附近考虑多量子数跃迁并计及原子复合的影响.对O2-Ar体系,计算给出了在正激波后O2分子振动能级分布、振动弛豫时间、离解孕育时间、离解产物浓度、离解速率系数等物理量随时间的演化.计算结果分别与Camac和Wray的实验相符.计算显示,在激波作用的后期,有准稳态的振动能级布居分布.计算结果显示,Park模型低估了非平衡离解速率系数,Hansen模型则高估了非平衡离解速率系数.

970nm抽运下Tm^3／Yb^3＋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（452n

980 nm 抽运下Yb-Tm-Ho 三掺氟磷酸盐玻璃的2 μm 荧光性质

The thermal stability, 2 μm fluorescence properties and energy transfer mechanism in Ho³⁺ doped fluorophosphate glass sensitized by Yb³⁺ and Tm³⁺ were investigated. The characteristic temperatures, absorption spectrum and fluorescence spectrum of the glass sample were measured. ΔT calculated from the characteristic temperatures shows that the thermal stability of fluorophosphate glass is better than fluoride glass. According to the absorption spectrum, several spectroscopic parameters of the glass sample, such as Judd-Ofelt parameters and spontaneous transition probability were calculated and compared with other glass hosts. The largest spontaneous transition probability for Ho³⁺:⁵ I7&rarr⁵I8 transition in fluorophosphate glass which is 78.48 s^-1 indicates that fluorophosphate glass is an appropriate base glass to achieve 2 m fluorescence. From the fluorescence spectrum of the glass sample, the extremely strong 2.0 μm fluorescence intensity is observed, which is higher than the intensity of 1.8 μm fluorescence, showing that Ho³⁺ ions sensitized by Yb³⁺ and Tm³⁺ is efficient. Meanwhile, the absorption sections and emission sections of Yb³⁺, Tm³⁺ and Ho³⁺ were calculated and the pumping scheme and energy transfer mechanism among Yb³⁺, Tm³⁺ and Ho³⁺ are discussed. The study indicates that Yb-Tm-Ho tri-doped fluorophosphate glass is a significant sensitization glass system under 980 nm excitation for 2 μm applications.

808 nm 抽运的Ho3+，Tm3+及Er3+掺杂的氟磷酸盐 玻璃的2.0 μm 光谱性质研究

2.0 μm spectroscopic properties of Er³⁺/Tm³⁺/Ho³⁺ triply-doped fluorophosphate glasses pumped by 808 nm and the energy transfer mechanisms between the three rare earth ions were investigated. J-O theory was used to calculate the parameters of Ho³⁺ in fluorophosphate glasses. Absorption and emission cross-sections and the gain coefficients were calculated. The obtained lifetime r and spontaneous transition probability Ar of Ho³⁺:⁵I7 level were 10.64 ms and 93.95 s^-1 respectively. The calculated maximum emission cross-section of 2.0 μm was 9.26×10^-21 cm². The energy transfer analysis indicated that the cross-relaxation of Tm³⁺ was important and the resonent energy transfer in Er³⁺&rarrHo³⁺, Tm³⁺&rarrHo³⁺, Er³⁺&rarrTm³⁺&rarrHo³⁺ process was the main channel. The study revealed that the Er³⁺/Tm³⁺/Ho³⁺ triply-doped fluorophosphate glass would be a potential material for 2.0 μm emission because of the efficient sensitization of Er³⁺ and Tm³⁺ to Ho³⁺.

Optical transitions and upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

Er3+-doped halide modified tellurite glasses were synthesized by conventional melting and quenching method. The Judd-Ofelt analysis was performed on the absorption spectra and the transition probabilities, excited state lifetimes, and the branching ratios were calculated and discussed. The intense infrared and visible fluorescence spectra under 980 nm excitation were obtained. Strong upconversion signal was observed at pumping power as low as 30 mW in the glasses with halide ions. The upconversion mechanisms and power dependent intensities were discussed, which showed two-photon process are involved for the green and red emissions. The decay times of the emitting states and the corresponding quantum efficiency were determined and explained. (C) 2004 American Institute of Physics.

Spectroscopic properties and thermal stability of Er3+/Yb3+-codoped fluorophosphate glasses

A comprehensive study on the thermal stability and spectroscopic properties of Er3+/Yb3+-codoped Al(PO3)(3)-based fluorophosphate glasses is reported of the 1.5μ m fibre amplifiers in this paper. From optical absorption spectra, the Judd-Ofelt parameters of Er3+ in the glasses and several important optical properties, such as the radiative transition probability, the branching ratio and the spontaneous emission probability, have been calculated by using Judd-Ofelt theory. The fluorophosphate glass exhibits broadband near-infrared emission at 1.53μ m with a full width at half-maximum over 63nm, and a large calculated stimulated-emission cross-section of 6.85 x 10(-21)cm(2).