Luminescence of Ce in hydrated rare earth bromides

Intense photoluminescence is reported for hydrated bromides of Gd, La and Y (LaBr₃·7H₂O, CeBr₃·7H₂O, YBr₃·8H₂O and GdBr₃·n H₂O) prepared by the wet chemical method and activated with Ce³⁺. Intensities are comparable to that for a commercial phosphor (SrB₄O₇:Eu²⁺—Sylvania 2052). Luminescence in hydrated salt is usually quenched. The observation of intense luminescence in hydrated bromides is remarkable.     

Gadolinium orthophosphate weinschenkite type and phase change in rare earth orthophosphates

Some properties of rare earth orthophosphates have been determined by means of synthesis, X-ray diffraction, infrared absorption spectra, and Raman spectra measurements. The results are: (1) a synthesis of new compounds GdPO₄.2H₂O weinschenkite type, (2) the salt readily lost its water and changed from the weinschenkite to the xenotime form at about 300°C in air, (3) the change phase in rare earth orthophosphates showed that the weinschenkite phase can give rise to rhabdophane or xenotime phases, and (4) the orthorhombic form DyPO₄·1.5H₂O is explainable in terms of a mixture of rhabdophane and xenotime-structured material.     

Spin-lattice relaxation times of rare earth ions in binary nitrates

The Van Vleck method is used with the point-charge model to calculate the spin-lattice relaxation times of the Ce³⁺ ion in binary nitrates. Normal coordinates are found for the icosahedral XY₁₂ complex containing the paramagnetic ion and its nearest neighborhood. The theoretical transition probabilities for the purely ionic model turn out to be slightly above the experimental results, so covalent effects are important.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 31–37, August, 1969.The author thanks L. K. Aminov for supervision of and assistance in this study.     

The magnetic hyperfine fields of rare earth ions in metals

Data for the magnetic dipole hyperfine interaction of essentially single rare earth ions in metals, measured with different experimental methods, are collected and discussed. Depending on the host, the magnetic hyperfine field of these paramagnetic ions remains undisturbed by the environment, or it is enlarged, or weakened or can even become completely lost. If there are magnetic ions in the neighbourhood, the magnetic interaction can enlarge the hyperfine field of the single ion by a transferred hyperfine field. The reason of the demagnetization effect may be crystal field splitting and hybridization. The core polarization field of the free rare earth ions is redetermined from measurements of the hyperfine interaction in nonmagnetic metals at low magnetic ion concentration.     

Luminescence studies of rare earth doped yttrium gadolinium mixed oxide phosphor

This paper reports the photoluminescence and thermoluminescence properties of gamma ray induced rare earth doped yttrium gadolinium mixed oxide phosphor. The europium (Eu³⁺) was used as rare earth dopant. The phosphor was prepared by chemical co-precipitation method according to the formula (Y_2−x−yGd_x) O₃: Eu_y³⁺ (x=0.5; y=0.05). The photoluminescence emission spectrum of the prepared phosphor shows intense peaks in the red region at 615 nm for ⁵D₀→⁷F₂ transitions and the photoluminescence excitation spectra show a broad band located around 220–270 nm for the emission wavelength fixed at 615 nm. The thermoluminescence studies were carried out after irradiating the phosphor by gamma rays in the dose range from 100 Gy to 1 KGy. In the thermoluminescence glow curves, one single peak was observed at about 300 °C of which the intensity increases linearly in the studied dose range of gamma rays. The glow peak was deconvoluted by GlowFit program and the kinetic parameters associated with the deconvoluted peaks were calculated. The kinetic parameters were also calculated by various glow curve shape and heating rate methods.     

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     

Theoretical description of the spectroscopic properties of rare earth ions in crystals

In this article the present state of knowledge of the theory of one- and two-photon processes observed in rare earth ions in crystals is presented. The conclusions are based on the results of ab initio calculations performed for various ions across the lanthanide series. The model applied for the calculations is based on the Rayleigh–Schrödinger perturbation theory, and the amplitude of a certain electric dipole transition is expressed in terms of effective operators. The radial integrals of the effective operators are defined by the perturbed functions that contain the perturbing influence of single excitations from the 4f shell to all one-electron states of a given symmetry, discrete and continuum. In this approach the interactions between the 4f^N and the excited configurations via the crystal field potential, the electron correlation operator and the spin–orbit interaction operator are discussed; it is believed that the presented theory contains the most important physical mechanisms responsible for the f↔f electric dipole transitions. Two alternative formulations of the theory of one-photon electric dipole transitions are presented. Consequently, the transition amplitude is defined within the standard theory based on the length formula and within a new approach which is based on the velocity form of the electric dipole radiation operator.     

Luminescence decay in AgCl crystals

The kinetics of luminescence decay of single crystal plates of AgCl was measured at the temperature of liquid nitrogen. Luminescence decay first takes place (fort≦2·5× ×10^?3 sec) according to a hyperbole and then according to an exponential. The constantsa anda of the hyperbolic andt of the exponential dependence were measured for different intensity of the exciting radiation in normal and deformed samples and in samples irradiated withb-particles during measurement.     

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。     

Luminescence decay in spray-pyrolyzed Cds

We report the room temperature luminescence decay of spray pyrolyzed CdS, which is extremely similar to the luminescence decay of amorphous silicon hydrogen alloys at liquid helium temperatures. We suggest that the luminescence decay in both of these materials is due to localized electrons and holes recombining by radiative tunnelling.     

Luminescence properties of SrSi2O2N2 doped with divalent rare earth ions

The optical properties of SrSi₂O₂N₂ doped with divalent Eu²⁺ and Yb²⁺ are investigated. The Eu²⁺ doped material shows efficient green emission peaking at around 540 nm that is consistent with 4f⁷→4f⁶5d transitions of Eu²⁺. Due to the high quantum yield (90%) and high quenching temperature (>500 K) of luminescence, SrSi₂O₂N₂:Eu²⁺ is a promising material for application in phosphor conversion LEDs. The Yb²⁺ luminescence is markedly different from Eu²⁺ and is characterized by a larger Stokes shift and a lower quenching temperature. The anomalous luminescence properties are ascribed to impurity trapped exciton emission. Based on temperature and time dependent luminescence measurements, a schematic energy level diagram is derived for both Eu²⁺ and Yb²⁺ relative to the valence and conduction bands of the oxonitridosilicate host material.     

Statistical mechanics of magnetic non magnetic transitions of rare earth ions in metals

Using a simple model, and by means of a phenomenological extension of the Green's function method, it has been possible to give a more precise mathematical footing to the ideas put forward by Hirst, Maple, Wohleben and Coles regarding the demagnetization of rare earth ions in metals.     

Laser spectroscopy of rare earth ions in lead borate glasses and transparent glass-ceramics

Rare earth doped lead borate glasses and transparent glass-ceramics have been studied using optical spectroscopy. Based on the absorption, emission and its decay and the Judd-Ofelt calculations, several radiative and laser parameters for Ln ³⁺ (Ln = Pr, Nd, Eu, Dy, Er, Tm) were evaluated. The large values of luminescence lifetime, quantum efficiency of excited state and room temperature peak stimulated emission cross-section suggest efficient laser transitions of Ln ³⁺ ions in lead borate glasses. The obtained results indicate that lead borate glasses and glass-ceramics containing Ln ³⁺ ions are promising host matrices for solid-state laser applications.