Energy transfer from Tb3+ to Eu3+ ions sorbed on SrTiO3 surface

The energy transfer at room temperature between Tb³⁺ and Eu³⁺ ions sorbed onto SrTiO₃ powders is investigated, using Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Several published works deal with the energy transfer between two lanthanide ions in co-doped matrices but it is the first time that transfer processes between two lanthanide ions sorbed on a solid surface is reported. The results show that the energy transfer between sorbed Tb³⁺ and Eu³⁺ ions on strontium titanate is a non-radiative process and follows a dipole–dipole type interaction. Moreover, the higher the acceptor ions Eu³⁺ concentration, the more efficient the energy transfer.It is shown that no energy migration between the Tb³⁺ donor ions occurs. A formalism based on the model of Inokuti–Hirayama is used and allows one to fit the non-exponential Tb³⁺ fluorescence decay. It is thus possible to evaluate the critical radius (R₀) of the influence sphere of the sorbed Tb³⁺ ions. According to the previous works, two sorption sites are considered for the sorbed rare-earth. The calculated radii are similar to those obtained for other couples of donor–acceptor lanthanide ions reported in the literature.     

等离子体效应对类氦氖Kα线系电偶极辐射的影响

采用离子球模型，通过自洽求解Boltzmann方程和Poisson方程，得到类氦氖离子Kα线系的两条电偶极辐射光谱能量随等离子体环境的漂移.结果显示，Kα线系电偶极谱线随等离子体电子密度增大发生红移，红移量与等离子体电子密度有近似的正比关系；随着等离子体电子温度的降低，光谱红移对等离子体电子密度的敏感性增大.另外，所研究的两条谱线间的能量间隔随等离子体电子密度的增大而减小，减小量随等离子体电子密度的变化也呈现出近似的线性规律.值得注意的是，类氦氖Kα线系中两条电偶极谱线分别为互组合线与共振谱线，而其能量差就是1s2p(³P₁)的交换能，因此进一步发现能级中交换能将随等离子体环境变化的规律.所观察到的光谱红移和精细结构分裂在高密度等离子体中都有明显的变化，对探索高密度等离子体的诊断新方法有重要意义. 关键词： 光谱漂移 交换能 等离子体 类氦离子     

Theoretical calculation of the dipole moment function of the aΠ state of NO

The potential energy curve and theoretical dipole moment function of the a⁴Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a⁴Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N⁺O⁻. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr.     

Theoretical calculation of the dipole moment function of the a4Π state of NO

The potential energy curve and theoretical dipole moment function of the a⁴Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a⁴Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N⁺O^?. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr.     

Analysis of Energy Transfer and Concentration Quenching in Sm3+-Activated Borate GdB3O6 Phosphors by Means of Fluorescence Dynamics

This article reports on the optical properties of Sm³⁺-activated GdB₃O₆ phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd³⁺ to Sm³⁺ and the concentration quenching of the Sm³⁺ ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd³⁺ to Sm³⁺ is confirmed. The concentration quenching of the Sm³⁺ ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm³⁺ ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm³⁺⁴G_5/2 level exhibiting a buildup and decay process also confirm the energy transfer from Gd³⁺ to Sm³⁺ and between Sm³⁺ ions.     

Ca8Mg(SiO4)4Cl2:Ce3+, Tb3+: A potential single-phased phosphor for white-light-emitting diodes

A single-phased white-light-emitting phosphor Ca₈Mg(SiO₄)₄Cl₂:Ce³⁺, Tb³⁺ (CMSC:Ce³⁺, Tb³⁺) is synthesized by a high temperature solid-state reaction method, and its photoluminescence properties are investigated. The obtained phosphor exhibits a strong excitation band between 250 and 410 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Energy transfer from Ce³⁺ to Tb³⁺ ions has been investigated and demonstrated to be a resonant type via a dipole–dipole mechanism. The energy transfer efficiency as well as the critical distance is also estimated. Furthermore, the phosphors can generate light from yellow-green through white and eventually to blue by properly tuning the relative ratio of Ce³⁺ to Tb³⁺ ions grounded on the principle of energy transfer. The results show that this phosphor has potential applications as a single-phased phosphor for UV white-light LEDs.     

液晶SmC*相自发极化的统计理论

采用格胞模型，定义在格胞中心上的极化序参量．选用双轴性并具有横向电矩的分子作用势，求得系统的自由能，得到自发极化强度的大小和螺旋变化螺距的表达式．计算了DOBAMBC和3M2CPOOB等4种典型SmC^*相液晶的自发极化强度大小和螺距随温度的变化及其受分子横向电矩的影响，结果与实验相符．表明SmC^*相的自发极化强度主要产生于分子的双轴性和横向电矩． 关键词：     

Angular momentum dependence of the giant dipole resonance width in excited nuclei of mass

Gamma ray spectra in the energy range of 4–25 MeV were measured in the reaction ²⁸Si + ¹²⁴Sn at E(²⁸Si) 150 MeV in coincidence with low energy γ-multiplicities. The spectra were analysed using a simulated Monte Carlo CASCADE code. The centroid energy and width of the giant dipole resonance were extracted for various multiplicity windows. The average angular momentum and temperature of the final states populated after the giant dipole photon emission range from 25 and 1.5 MeV to 56 and 1.3 MeV, respectively. The extracted widths are almost constant for the lower multiplicity windows and show an increase of 1.4 MeV at the highest window. The nuclei are expected to be near the liquid drop regime and the experimental results are not inconsistent with the liquid drop behaviour.     

The luminescence enhancement of Eu3+ ion and SnO2 nanocrystal co-doped solben gel SiO2 films

SnO₂ nanocrystal and rare-earth Eu³⁺ ion co-doped SiO₂ thin films are prepared by sol-gel and spin coating methods. The formation of tetragonal rutile structure SnO₂ nanocrystals with a uniform distribution is confirmed by X-ray diffraction and transmission electron microscopy. Fourier transform infrared spectroscopy is used to investigate the densities of the hydroxyl groups, and it is found that the emission intensity from the ⁵D₀-⁷F₂ transitions of the Eu³⁺ ions is enhanced by two orders of magnitude due to energy transfer from the oxygen-vacancy-related defects of the SnO₂ nanocrystals to nearby Eu³⁺ ions. The influences of the amounts of Sn and the post-annealing temperatures are systematically evaluated to further understand the mechanism of energy transfer. The luminescence intensity ratio of Eu³⁺ ions from electric dipole transition and magnetic dipole transition indicate the different probable locations of Eu³⁺ ions in the sol-gel thin film, which are further discussed based on temperature-dependent photoluminescence measurements.     

Crystal field and spectrum of Pr4+ in BaPrO3

We have measured the absorption spectrum of BaPrO₃ in the spectral range 1900–11000 cm⁻¹. All the energy levels of the 4f electronic configuration of the Pr⁴⁺ ion in a crystal have been observed for the first time. We describe the total set of electron-nuclear states and the integral intensities of the magnetic dipole transitions of the Pr⁴⁺ in BaPrO₃ in the framework of the crystal field approximation. The crystal field parameters corresponding to the real orthorhombic symmetry of BaPrO₃ are obtained with the exchange charge model.     

The electronic structure of KMnO4 investigated by photoemission and electron-energy-loss spectroscopy

From photoemission and electron-energy-loss data the following picture of KMnO₄, with Mn^VII (with a formal charge state Mn⁷⁺ (3d ⁰)) tetrahedrally surrounded by four O^2–-ions, is deduced: strong covalent bonding between Mn^VII and O^2– leads to a considerable occupation of the Mn-3 d shell. The ground state of the (MnO₄)^–1 molecule is an orbital and spin singlet as seen by the absence of any multiplet splitting in the Mn core levels. The valence band shows a four peak structure extending form 4 eV to 8 eV below the Fermi energy. The first peak at 4.2 eV has mainly O-2p character. The remaining peaks are of strongly mixed Mn-3d/O-2p character due to the covalent bonding. This mixing decreases with increasing binding energy. The electron energy loss data show a variety of structures between 2 eV and 10 eV independent of the primary electron energy which defines them as dipole allowed charge-transfer transitions. An additional excitation at 1.8 eV decreases quickly in intensity with increasing electron energy which classifies it as a dipole or spin forbidden transition in the compound. This energy is close to the value of 1.6 eV reported for the activation energy observed in electrical transport data. The results are compared to quantum chemical molecular orbital calculations of the (MnO₄)^–1 molecule.Physics Department, Allahabad University Allahabad 211002, India     

Excited state dynamics and energy transfer rates in Sr3Tb0.90Eu0.10(PO4)3

The emission spectrum of neat Sr₃Tb(PO₄)₃ upon excitation at 337 nm in the levels above ⁵D₃ is dominated by ⁵D₄ emission and no significant emission from ⁵D₃ is observed due to efficient cross relaxation involving the Tb³⁺ levels. On the other hand, the emission spectrum of the same host containing 10 mol% Eu³⁺ upon excitation at the same wavelength (in the Tb³⁺ levels) is dominated by strong emission bands from the ⁵D₀ level of Eu³⁺. This clearly indicates that Tb³⁺→Eu³⁺ energy transfer is present. The excitation spectrum of the Eu^{3+ 5}D₀ emission is dominated by Tb³⁺ bands extending in the UV region.The presence of 10 mol% Eu³⁺ in Sr₃Tb(PO₄)₃ very strongly shortens the ⁵D₄ decay time. The decay curve is not far from exponential, indicating that the energy transfer to Eu³⁺ is accompanied by fast energy migration. The transfer regimes are identified and the donor–donor and donor–acceptor transfer microparameters are quantified under the assumption of electric dipole–electric dipole interactions.     

Electrofission of238U and232Th

Absolute electrofission cross sections for²³⁸U and²³²Th in the energy regionE _e =7 ?65 MeV and fission fragment angular distributions forE _e =7–30 MeV have been measured. The angular distributions show strong anisotropies for low energies. The relative dipole and quadrupole contributions as a function of excitation energy are discussed in terms of the low lying fission transition states above the fission barriers. The cross sections show significant deviations from the results of some earlier measurements, in particular in the energy region above the giant dipole resonance. From the difficulties of absolute electrofission cross section measurements and the ambiguities in their interpretation it is concluded that by this time the quantitative analysis of electrofission cross sections with respect to the contributions of the giant quadrupole resonances to the fission decay channel should be regarded as rather tentative.     

Thermal stability and UV–Vis-NIR spectroscopy of a new erbium-doped fluorotellurite glass

A new transparent bulk glass from the system 76TeO₂?·?10ZnO?·?9.0PbO?·?1.0PbF₂?·?3.0Na₂O doped with Er³⁺ (TZPPN doped with Er³⁺) has been prepared using the conventional melt-quenching method. Results of differential thermal analysis (DTA) measurements indicate good thermal stability of this glass. The refractive indices at different wavelengths, the optical energy gap, the Sellmeier gap energy and the dispersion energy have been estimated. The Judd–Ofelt parameters, Ω _t (t?=?2,?4,?6) of Er³⁺ were evaluated from optical absorption spectra. Electric dipole, magnetic dipole type transition probabilities, spectroscopic quality factors, branching ratio and radiative lifetimes of several excited states of Er³⁺ have been predicted using intensity Judd–Ofelt parameters. The spectroscopic properties indicate that TZPPN glass doped with Er³⁺ is a promising candidate for laser applications and may be suitable for upconversion fibre optical devices.     

Editorial

Using coupled cluster singles and doubles linear response theory and the d-aug-cc-pVTZ basis set extended with a 3s3p2d1f1g set of midbond functions, the interaction induced electric dipole polarisability surface of the CO–Ar van der Waals complex is computed. Combining this surface with accurate intermolecular potential energy and electric dipole surfaces, the pressure and dielectric second virial coefficients of the complex are calculated by a classical statistical approach. Excellent agreement with experimental results (to within the experimental error bars) is obtained for the pressure second virial coefficient over a range of temperatures. No previous experimental or theoretical investigations have been carried out for the dielectric second virial coefficient, B _ε(T), which is estimated to be about 1.9 cm⁶ mol^??1 at room temperature. This value results from a balance of terms due to the interaction induced electric dipole polarisability (predominant at high temperatures) and orientational electric dipole contributions.     

11Li,14Be和17B核的软偶极共振模式

假定¹¹Li,¹⁴Be和¹⁷B核是由核芯和两个外层中子所组成,用Sum Rule探讨这类核的巨偶极共振,给出软偶极共振的能量和强度。结果与其它理论计算进行了比较。 关键词：     

Cooperative phenomena of random electric dipoles in an amorphous matrix

A ferroelectric phase transition has been observed for the first time in a series of glasses containing WO₆-octahedra. The techniques of thermally stimulated depolarization currents were used to observe the transition from independent dipole behavior to cooperative behavior in this amorphous system as a function of concentration. These measurements yielded the activation energy ΔE=1.2eV, the pre-exponential τ₀=2 × 10^-22sec, and the dipole moment p?=1.3 × 10^?15 esu cm for WO₃ in Li₂B₄O₇. A dipole moment bearing species due to Li₂B₄O₇ was observed with ΔE=0.44eV and pre-exponential τ₀=5 × 10^?8 sec. The depolarization peaks of WO₃ occur in the temperature range 265–275 K depending upon WO₃ concentration and are pressure dependent with an initial slope of 2 × 10^?5K dyne^?1 cm². A model was developed for a possible phase transition associated with a random “pseudo-spin” system in an amorphous matrix.     

Time Resolved Fluorescence and Energy Transfer Analysis of Nd<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript>–Er<Superscript>3+</Superscript> Triply-Doped Ba–Al-Metaphosphate Glasses for an Eye Safe Emission (1.54 μm)

This paper reports on the preparation and systematic analysis of energy transfer mechanisms in Nd³⁺–Yb³⁺–Er³⁺ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence of Nd³⁺ in triply doped Ba–Al-metaphosphate glasses have revealed that, Yb³⁺ ions could function as quite efficient bridge for an energy transfer between Nd³⁺ and Er³⁺ ions. As a result, a fourfold emission enhancement at 1.54 μm of Er³⁺ ions has been achieved through an excitation of ⁴F_5/2 level of Nd³⁺ at 806 nm for the glass having 3 mol% Yb³⁺ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd³⁺) ion fluorescence has been analyzed based on theoretical models such as direct energy transfer model (Inokuti–Hirayama) and migration assisted energy transfer models (Burshtein’s hopping and Yokota–Tanimoto’s diffusion). The corresponding energy transfer parameters have been evaluated and discussed. Primarily, electrostatic dipole–dipole (s ~ 6) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses.     

High spin investigation in 193Pb with EUROGAM 2: coexistence of superdeformed and dipole bands

The nucleus ¹⁹³Pb was populated via the ¹⁶⁸Er(³⁰Si, 5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole ΔI = 1 cascades have been found. The ¹⁹³Pb dipole bands are discussed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two-quasiproton excitation coupled to rotation aligned quasineutrons. Parallel to the dipole bands the six superdeformed bands have been discussed in the framework of microscopic mean-field calculations. The bands are interpreted as three pairs of signature partners based on quasineutron excitations. Cross-talk transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, a mean B(M1)/B(E2) ratio value of 0.15±0.04 μ _N ² /e^2b2 has been extracted.     

Small broadening of the Mössbauer gamma line of the isomer <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag as yet another indication of the protracted character of the emission of photons from nuclei and their absorption

Nine experiments performed to date by three research groups in order to observe the Mössbauer effect in the case of gamma rays emitted by the long-lived isomer ^109m Ag yielded results suggesting an anomalously small broadening of the Mössbauer gamma line of this isomer. In turn, this indicates that the emission of photons from nuclei and their resonance absorption cannot proceed within a time interval much shorter than the characteristic time of the change in the energy of hyperfine dipole—dipole interaction, because the photon energy would otherwise be determined by the sum of the instantaneous value of the energy of this interaction and the nuclear-transition energy, in which case the broadening of the Mössbauer gamma line would reach five to six orders of magnitude, as opposed to one to two orders of magnitude broadening observed experimentally.