Time resolved investigations of energy transfer in Eu3+∶Y2O3

The concentration dependence of the energy transfer from the Eu³⁺ ions at lattice sites of point symmetryC ₃ i to the Eu³⁺ ions at lattice sites of point symmetryC ₂ in Y₂O₃ has been investigated by analyzing the nonexponential fluorescence decay curves of the donors measured after excitation by a short optical light pulse. The simple model of a fixed interaction rangeR ₀ proved to be adequate to explain the experimental observations. An interaction range ofR ₀=8.7 Å was found in agreement with previous steady state experiments.     

Energy levels and interaction between Eu3+-ions at lattice sites of symmetryC 2 and symmetryC 3i in Y2O3

Besides the known energy levels of Eu³⁺ at lattice sites of symmetryC ₂ in Y₂O₃, some transitions of this ion at lattice sites of symmetryC _3i in the same host crystal have been found and it was possible to construct the energy level scheme in part. Evidence for an energy transfer from Eu³⁺(C _3i ) to Eu³⁺(C ₂) is given, the strength of which is measured as a function of the Eu₂O₃ concentration. The results lead to the assumption of a fixed distanceR ₀ for the interaction responsible for the energy transfer. A temperature-independent value ofR ₀=8.7 Å was found. The full explanation of the underlying quantum mechanical mechanism requires further experiments.     

Paramagnetische Resonanz von Er3+ und Ce3+ in Y2O3

The paramagnetic resonance of trivalent Er and Ce in single crystals of Y₂O₃ on sites of crystal field symmetryC _3i andC ₂ is investigated at 9.5 kMe/s. For Er³⁺ ions completing results to formerly published data are given. For Ce: Y₂O₃ the measured values of theg-tensors are:g _‖=0.394 andg _⊥=1.633 forC _3i -sites andg _z =0,g _x =2.938,g _y =0.819 forC ₂-sites. For ions on sites of symmetryC ₂ the principal axesx andy ofg are tilted 29.7° against the [100] directions.     

Site-selective laser spectroscopy of BaF2:Eu3+

The selective laser excitation of the flourescence of Eu³⁺ ions is used to investigate the defect sites in BaF₂:Eu³⁺ for Eu³⁺ concentrations ranging from 0.03 to 2.43 mol%. We identified the fluorescence lines arising from the (Eu³⁺, F^-_i) dipole of C_3v symmetry and established its energy level diagram. The compensating ion is an interstitial F^-_i ion located in the next-nearest-neighbour site, with respect to the Eu³⁺ ion. This (Eu³⁺, F^-_i) dipole dominates in BaF₂. Fluorescence lines assignable to next-nearest-neighbour pairs of (Eu³⁺, F^-_i) dipoles have been found above 0.1 mol% dopant concentration.     

Energy transfer between Eu3+ ions in a lattice with two different crystallographic sites: Y2O3:Eu3+, Gd2O3:Eu3+ and Eu2O3

The Eu³⁺ ion occupies two different crystallographic sites in (Y_1−xEu_x)₂O₃ and (Gd_1−xEu_x)₂O₃, with site symmetry S₆ and C₂. Energy transfer over more than 7 Å occurs from Eu³⁺ (S₆) ions to Eu³⁺ (C₂) ions. This is shown to be a direct one-phonon assisted process, in combination with a one-site resonant two-phonon assisted process at higher temperatures. For x = 1 there is energy migration over the Eu³⁺ (C₂) sublattice to quenching impurities. The presence of cooperative absorption points to superexchange interaction between the Eu³⁺ ions.     

Improved luminescence of Y2MoO6:Eu3+ by doping Li+ ions for light-emitting diode applications

The photoluminescence (PL) property of Y₂MoO₆:Eu³⁺ doped with Li⁺ is investigated in this paper. The red luminescence of Eu³⁺ in Y₂MoO₆ lattice has greatly enhanced by codoping monovalent alkali metal ions Li⁺ into the lattice. The drastic increase in the luminescence intensity of Y_2?xLi_xMoO₆:Eu³⁺ originates from the reason that the Li⁺ ions may serve as a self-promoter for better crystallization to reduce the defect or as a lubricant for the complete incorporation of the Eu³⁺ ions into the Y₂MoO₆ host.     

Fast excited-state relaxation of Eu-Eu pairs in commercial Y2O3: Eu3+ phosphors

Low-temperature, dye-laser excitation spectroscopy of commercial Y₂O₃:Eu³⁺ phosphors reveals the presence of complex structure in the excitation lines of the ⁵D₀ and ⁵D₁ manifolds. The structure is associated with the presence of Eu³⁺ ion pairs. The kinetics of the emission decay are observed to be drastically different when excitation occurs either at the center or on the wings of the excitation lines, suggesting faster inter-level and/or inter-site energy transfer on exciting into the line wings. Low-temperature vibronic spectra are reported for the ⁷F₀→⁵D₀ transitions for both C₂ and C_3i sites. Evidence is presented for the detection of the highly forbidden ⁷F₀→⁵D₀ transition for the C_3i site.     

Sensitized red luminescence from Bi co-doped Eu: ZnO-B2O3 glasses

Photoluminescence properties of Bi³⁺ co-doped Eu³⁺ containing zinc borate glasses have been investigated and the results are reported here. Bright red emission due to a dominant electric dipole transition ⁵D₀→⁷F₂ of the Eu³⁺ ions has been observed from these glasses. The nature of Stark components from the measured fluorescence transitions of Eu³⁺ ions reveal that the rare earth ions could take the lattice sites of C_s or lower point symmetry in the zinc borate glass hosts. The significant enhancement of Eu³⁺ emission intensity by 346 nm excitation (¹S₀→³P₁ of Bi³⁺ ions) elucidates the sensitization effect of co-dopant. The energy transfer mechanism between sensitizer (Bi³⁺) and activator (Eu³⁺) ions has been explained.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

Influence of alkali metal ions doping content on photoluminescence of (Y, Gd) BO3:Eu red phosphors under VUV excitation

The red-emitting Y_0.65−xGd_0.25M_xBO₃:0.10Eu³⁺ (M=Li, Na, K 0.00≤x≤0.10) phosphors were synthesized by solid-state reaction and their photoluminescence characteristics were studied under vacuum ultraviolet (VUV) excitation. The emission intensity is significantly improved by adding alkali metal ions dopants because they introduce some bounded electron−hole pairs, which act as an intermediator for the excitation energy transfer from the host lattice to the activator Eu³⁺. The chromaticity was improved due to the distorted surrounding of Eu³⁺. The emission intensity of the Y_0.65−xGd_0.25 M_xBO₃:0.10Eu³⁺ increased up to maximum with alkali metal ions doped to a certain concentration and then decreased with the increase in of alkali metal dopants.     

Broadband,site selective and time resolved photoluminescence spectroscopic studies of finely size-modulated Y2O3:Eu3+ phosphors synthesized by a complex based precursor solution method

Undoped and Eu³⁺-doped cubic yttria (Y₂O₃) nanophosphors of good crystallinity, with selective particle sizes ranging between 6 and 37 nm and showing narrow size distributions, have been synthesized by a complex-based precursor solution method. The systematic size tuning has been evidenced by transmission electron microscopy, X-ray diffraction, and Raman scattering measurements. Furthermore, size-modulated properties of Eu³⁺ ions have been correlated with the local structure of Eu³⁺ ion in different sized Y₂O₃:Eu³⁺ nanophosphors by means of steady-state and time-resolved site-selective laser spectroscopies. Time-resolved site-selective excitation measurements performed in the ⁷F₀ → ⁵D₀ peaks of the Eu³⁺ ions at C₂ sites have allowed us to conclude that Eu³⁺ ions close to the nanocrystal surface experience a larger crystal field than those in the nanocrystal core. Under the site-selective excitation in the ⁷F₀ → ⁵D₀ peaks, energy transfer between the sites has also been observed.     

Control of photoluminescence in Ca3–3x /7Y2x /7(PO4)2:Eu2+ phosphors by migration of the dopant

A series of Ca_{3–3x /7}Y_{2x /7}(PO₄)₂:Eu²⁺ phosphors were synthesized by conventional solid‐state reaction. The photoluminescence spectra elucidate that the evolution of emission hue from violet–blue to blue–greenish could be realized by incorporating Y³⁺ ions. The aliovalent substitution of Y³⁺ for Ca²⁺ forms cationic vacancies (h denotes a vacancy) at Ca(4) site according to the formula 3Ca²⁺ = 2Y³⁺ + h, and then facilitates the migration of dopant Eu²⁺ from Ca(4) site to other sites in host lattice. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spectra of europium-doped yttrium oxide and yttrium vanadate phosphors

The spectral distributions of the visible absorption and fluorescence emission under electron beam excitation of Eu³⁺-doped (Y₂O₃) and (YVO₄) powders have been detected and analyzed. (Y₂O₃: Eu³⁺) has a cubicC crystal structure with a unit cell dimension a=10·61 Å. Its observed transitions from⁷ F ₀ to many upper states have been recognized; the observed number of Stark components is in agreement with that based on theC ₂ site symmetry of the Eu³⁺ ion in Y₂O₃. Eu³⁺-doped yttrium vanadate has a typical zircon tetragonal crystal structure with unit cell dimensions ofc=6·29 Å anda=7·11 Å. The observed transitions in (Eu³⁺: YVO₄) have been identified and assigned in accordance with theD _2d site symmetry of the Eu³⁺ ion in this lattice.The authors would like to express their deep gratitude to Professor G. F. J.Garlick, University of Hull, England, for offering experimental facilities in his Physics Department.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Far-infrared spectra of Strontium Fluoride doped with rare earth

Far-infrared measurements (17–170 cm⁻¹) are reported for SrF₂:RE³⁺ (RE = Pr, Nd, Tb, Dy, Ho, Er, Tm).The vibrations of the F⁻_i compensation ions reveal the local symmetry (Oh, C_4v, C_3v). The concentration of ions in each local site and the frequencies of the F⁻_i vibrations in the C_4v site show a regular evolution vs RE ionic radii.The study of electronic transitions within the ground manifold of the RE ions shows a similar evolution. For Dy³⁺ we detect lines already attributed to C_3v (F⁻_i) sites. New lines observed with Er³⁺ and Dy³⁺ can be attributed to C_4v (F⁻_i) sites, and the crystal field parameters that we have calculated are close to those of the C_4v (F⁻_i) site in CaF₂.For Nd³⁺ the electronic line is close to a C_4v level observed by EPR.     

Structural,photoluminescent, and dielectric properties of Eu3+-doped Ba0.7Sr0.3TiO3 thin films

Eu³⁺-doped Ba_0.7Sr_0.3TiO₃ thin films were prepared by a chemical solution deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence and dielectric measurements. The thin films were well crystallized with a pure perovskite structure. A contraction of the unit cell was observed upon incorporation of Eu³⁺ ions below 2 mol%, while an expansion occurred as the Eu³⁺ concentration was further increased above 2 mol%, indicating that Eu³⁺ ions with different concentrations occupied different lattice sites. Photoluminescence spectra showed two prominent transitions of Eu³⁺ ions at 594 nm (⁵D₀ → ⁷F₁) and 618 nm (⁵D₀ → ⁷F₂) upon excitation at 395 nm (⁷F₀ → ⁵L₆). There existed two quenching concentrations at 2 mol% and 4 mol% due to different lattice sites of the Eu³⁺ ions. We also investigated the dielectric properties of the thin films. Our study suggests that Eu³⁺-doped Ba_0.7Sr_0.3TiO₃ thin films have potential applications in multifunctional optoelectronic devices.     

Effect of Eu,Tb codoping on the luminescent properties of Y2O3 nanorods

Red-emitting Y₂O₃:Eu³⁺ and green-emitting Y₂O₃:Tb³⁺ and Y₂O₃:Eu³⁺, Tb³⁺ nanorods were synthesized by hydrothermal method. Their structure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The photoluminescence (PL) property of Y₂O₃:Eu³⁺,Tb³⁺ phosphor was investigated. In the same host (Y₂O₃), upon excitation with ultraviolet (UV) irradiation, it is shown that there are strong emissions at around 610 and 545 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺ and ⁵D₄-⁷F₅ transition of Tb³⁺, respectively. Different qualities of Eu³⁺and Tb³⁺ ions are induced into the Y₂O₃ lattice. From the excitation spectrum, we speculate that there exists energy transfer from Tb³⁺ to Eu³⁺ ions .The emission color of powders reveals regular change in the separation of light emission. These powders can meet with the request of optical display material for different colors or can be potentially used as labels for biological molecules.     

Luminescence and energy transfer in Y2O3 CO-doped with Bi3+ and Eu3+

The emission spectra and decay times of the Y₂O₃ CO-doped with Bi³⁺ and Eu³⁺ have been investigated using site-selective excitation and time-resolved spectroscopy in the temperature range 8–296 K. Evidence for an energy transfer from Eu³⁺(S₆) to Eu³⁺(C₂) is given. The critical transfer distance R₀ = 8.6 Å was found from the decay curve.     

Y2O3: Eu,Dy的制备与红色长余辉发光性能研究

采用高温固相法合成发光样品Y₂O₃：Eu³⁺_0.01和Y₂O₃：Eu³⁺_0.01,Dy³⁺_0.01.X射线衍射分析(XRD)表明样品保持Y₂O₃晶格结构,掺入的Eu³⁺和Dy³⁺对Y_{2关键词： 长余辉 2}O₃')" href="#">Y₂O₃ 稀土掺杂 陷阱     

Photoluminescence of Y2O3:Eu thin film phosphors by sol-gel deposition and rapid thermal annealing

Y₂O₃:Eu³⁺ phosphor films have been developed by using the sol-gel process. Comprehensive characterization methods such as Photoluminescent (PL) spectroscopy, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the Y₂O₃:Eu³⁺ phosphor films. In this experiment, the XRD profiles show that the Y₂O₃:Eu³⁺ phosphor films crystallization temperature and optimum annealing temperature occur at about 650 and 750 °C, respectively. The optimum dopant concentration is 12 mol% Eu³⁺ and the critical transfer distance (R_c) among Eu³⁺ ions is calculated to be about 0.84 nm. Vacuum environment is more efficient than oxygen and nitrogen to eliminate the OH content and hence yields higher luminescent phosphor films. The PL emission intensity of Y₂O₃:Eu³⁺ phosphor films is also dependent on the annealing time. It was found that the H₂O impurities were effectively eliminated after annealing time of 25 s at 750 °C in vacuum environment. From the experiment results, the schematic energy band diagram of Y₂O₃:Eu³⁺ phosphor films is constructed.