Directional emission from rare earth ions in inverse photonic crystals

Angular distribution of the photoluminescence from trivalent rare earth ions (Eu³⁺) embedded inside a magnesium silicate photonic crystal with an inverse opal structure is experimentally and theoretically studied. The emission at frequencies near the first stop-band of the photonic crystal is shown to exhibit strong angular modulation. The angle-dependent Eu³⁺ photoluminescence is numerically simulated by evaluating the fractional density of optical states in the photonic crystal, with diffuse scattering on structural imperfections taken into account. Experimental data for the emission properties of thin inverse opal films are shown to be in agreement with the simulation results. PACS 42.70.Qs; 78.55.-m     

High field electrical properties of CdF2 crystals doped with rare earth ions

The electrical properties of CdF₂ crystals doped with Eu³⁺ and Gd³⁺ are described. A reversible “forming” effect is observed under high electric fields. The effect seems to be connected with a reversible modification of the potential barrier at the metal-insulator contact.     

纳米晶体中稀土离子的发光性质及其变化机理研究

近年来, 纳米晶体中稀土离子发光性质的研究越来越受到人们的广泛关注, 这是因为纳米稀土发光材料在发光、高清显示、光电子纳米器件、生物荧光标记、激光和闪烁体等众多领域有着重要的应用前景。本项目采用软化学合成方法如水热法、溶胶-凝胶法等, 通过合成工艺的调控, 设计并合成出一系列不同颗粒尺寸、分散均匀、形貌可控的稀土离子掺杂氧化物(氟化物)微/纳米晶体, 利用激发、发射、漫反射以及高分辨激光光谱等光谱分析手段对其发光性质进行研究, 弄清影响发光行为的本质原因。同时, 结合光谱实验数据, 利用密度泛函理论和复杂晶体化学键介电理论方法进行理论计算, 成功解释了光谱变化规律和不同稀土离子间能量传递机理, 为相关稀土光谱研究奠定了理论和实验基础。     

Electron-correlation third-order contributions to the electric dipole transition amplitudes of rare earth ions in crystals

In ab initio studies of the impact of electron correlation effects of f ? f transition probabilities much numerical work is concerned with evaluating radial factors. These terms are expressed as products of the radial integrals summed over all excited orbitals including those in the continuum. To simplify the evaluation of these sums, for the first time in f ? f transition theory, the perturbed-function approach has been applied. The detailed analysis of numerical results obtained for the radial factors contributing to the transition amplitudes for Pr³⁺ are presented. Special attention is paid to studying the impact of the incompleteness of the radial basis set upon the radial factors occurring in f ? f electric-dipole transition theory.     

Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y₂SiO₅ (YSO), Lu₂SiO₅ (LSO), (Lu_0.5Y_0.5)₂SiO₅ (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm⁻¹ region assigned to the modes of SiO₄ and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm⁻¹ are an indication of impurities. The (SiO₄)⁴⁻ tetrahedra are characterized by bands near 200 cm⁻¹ which show a separation of the components of ν₄ and ν₂, in the 500–700 cm⁻¹ region which are attributed to the distorting bending vibration and in the 880–1000 cm⁻¹ region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm⁻¹ region of Re₂SiO₅ were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron correlation third-order contributions to the electric dipole transition amplitudes of rare earth ions in crystals

A complete expression for the f?f transition amplitude defined up to the third order in perturbation theory is presented. The third-order contributions are due to electron correlation inside the rare earth ion and arise from the static and dynamic models. The approach is formulated by means of double perturbation theory and in terms of effective tensor operators expressed by unit tensor operators. The discussion of the relative importance of various kinds of effective operators is based on the numerical results of test ab initio calculations performed within the perturbed function approach for the Pr⁺³ ion.     

Relativistic description of deformed rare earth nuclei

Ground state properties of heavy deformed nuclei in the rare earth region are described in the framework of the relativistic Hartree approximation. Both linear and non-linear parameter sets of the lagrangian are used. The non-linear sets reproduce the experimentally observed binding energies, the charge radii and the quadrupole moments, with the same quality as non-relativistic density dependent mean field calculations with Skyrme forces.     

Phase changes in cubic rare earth crystals

An explanation is offered of the structural transitions and magnetic orderings in the cubic rare earth compounds LnX with particular emphasis on the anomalous spin arrangements observed in HoP, DyP and DyAs and in ErSb and ErP.     

Conduction electron polarization in ferromagnetic rare earth crystals

We show that the average spin per atom in ferromagnetic rare earth metals is enhanced by means of a net spin polarisation of conduction electrons, arising as a consequence of multiple scattering of the conduction electrons.     

Magnetic properties of the rare earth pnictides

The magnetic properties of the binary rare-earth compounds with the nitrogen-group elements are briefly discussed, emphasizing the NaCl-type phases, for which the main magnetic data are collected.     

The effects of electron-phonon interaction on luminescence spectra of rare earth and transition metal impurity ions in crystals

The theory of electron-phonon interaction, based on the point-ion crystal field model, makes it possible to study multi-phonon transitions, shift and broadening of zero-phonon lines and other phenomena from a unified point of view. The theory based on a simple local centre model, including impurity centre ions and oscillating nearest neighbour point ions provides a satisfactory quantitative interpretation of electron-phonon interaction effects in the case of a small dynamic Jahn—Teller effect.     

14th International Feofilov Symposium on spectroscopy of crystals doped with rare earth and transition metal ions

Condensed-Matter Spectroscopy

14th International Feofilov Symposium on spectroscopy of crystals doped with rare earth and transition metal ions