Synthesis of Gd3PO7:Eu nanospheres via a facile combustion method and optical properties

Eu³⁺-doped Gd₃PO₇ nanospheres with an average diameter of ∼300 nm and a narrow size distribution have been prepared by a facile combustion method and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. The luminescent properties were systemically studied by the measurement of excitation/emission spectra, and emission spectra under different temperatures, as well as by photostability. The strong red-emission intensity peaking at 614 nm originates the ⁵D₀→⁷F₂ transition and is observed under 254-nm irradiation, indicating that Eu³⁺ ions in Gd₃PO₇ mainly occupied non-centrosymmetry sites. The CIE1931 XY chromaticity coordinates of Gd₃PO₇:Eu³⁺ nanospheres are (x=0.654, y=0.345) in the red area, which is near the National Television Standard Committee standard chromaticity coordinates for red. Thus, Gd₃PO₇:Eu³⁺ nanospheres may be potential red-emitting phosphors for PDP and Xe-based mercury-free lamps.     

Preparation and optical properties of SrF2:Eu nanospheres

SrF₂:Eu³⁺ nanospheres with homogeneous diameter have been synthesized by a microemulsion-mediated hydrothermal method for the first time, in which quaternary microemulsion of CTAB/water/cyclohexane/n-pentanol was used. The possible reaction mechanism and the luminescent properties of SrF₂:Eu³⁺ nanospheres were also investigated in this paper. The morphology and grain sizes of final products were characterized by field emission scanning electron microscopy and transmission electron microscopy, indicating that most of the products were nanospheres with an average diameter of ∼50 nm. Room-temperature emission spectra, recorded under 394-nm excitation, showed that the transition of ⁵D₀ → ⁷F₁ emission be dominating in SrF₂:Eu³⁺ nanospheres. From the dependence of the luminescence intensity on the concentration of Eu³⁺ ions, the optimal dopant concentration is 2 mol%.     

Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd³⁺ in diluted solid solutions of Gd₂O₃ in CeO₂ have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn²⁺:CeO₂ samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd³⁺:CeO₂ samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd₂O₃-CeO₂ diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO₂ solid solutions. It is not clear why clustering effects are present in Mn:CeO₂ solid solutions and not in Gd:CeO₂ solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn²⁺ (81 pm) is about 25% smaller that that of Gd³⁺ (107.8 pm). In any case, the fact that Gd:CeO₂ solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO₂ samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd³⁺ ions in CeO₂ is about 0.89 nm.     

Sonochemical synthesis and luminescence properties of single-crystalline BaF2:Eu nanospheres

BaF₂ nanocrystals doped with 5.0 mol% Eu³⁺ has been successfully synthesized via a facile, quick and efficient ultrasonic solution route employing the reactions between Ba(NO₃)₂, Eu(NO₃)₃ and KBF₄ under ambient conditions. The product was characterized via X-ray powder diffraction (XRD), scanning electron micrographs (SEM), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra. The ultrasonic irradiation has a strong effect on the morphology of the BaF₂:Eu³⁺ particles. The caddice-sphere-like particles with an average diameter of 250 nm could be obtained with ultrasonic irradiation, whereas only olive-like particles were produced without ultrasonic irradiation. The results of XRD indicate that the obtained BaF₂:Eu³⁺ nanospheres crystallized well with a cubic structure. The PL spectrum shows that the BaF₂:Eu³⁺ nanospheres has the characteristic emission of Eu^{3+ 5}D₀-⁷F_J (J=1-4) transitions, with the magnetic dipole ⁵D₀-⁷F₁ allowed transition (590 nm) being the most prominent emission line.     

Synthesis and characterization of Gd2O3:Eu phosphor nanoparticles by a sol-lyophilization technique

The characterization and luminescence properties of nanostructured Gd₂O₃:Eu³⁺ phosphors synthesized by a sol-lyophilization process are presented. After preparation of gadolinium-based sols from gadolinium nitrate and ammonium hydroxide, the so-prepared sols were freeze dried at −10°C and calcinated at different temperatures. For temperatures lower than 1300 K, highly crystalline samples with the cubic structure can be obtained without concomitant grain growth of the particles (<50 nm). The luminescence spectra contain all possible transitions of Eu³⁺ with C₂ symmetry and present two major features: an increase of the luminescence efficiencies of the phosphors in comparison with that obtained by solid-state reaction and the presence of an additional peak at about 609 nm at the vicinity of the ⁵D₀→⁷F_0…4 transition.     

Y2O3:Eu (5 mol%) with Ag nanoparticles prepared by citrate precursor

Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) and Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) containing 1 mol% of Ag nanoparticles were prepared by heat treatment of a viscous resin obtained via citrate precursor. TEM and EDS analyses showed that Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) is formed by nanoparticles with an average size of 12 nm, which increases to 30 nm when Ag is present because the effect of metal induced crystallization occurs. Ag nanoparticles with a size of 9 nm dispersed in Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) were obtained and the surface plasmon effect on Ag nanoparticles was observed. The emission around 612 nm assigned to the Eu³⁺ (⁵D₀→⁷F₂) transition enhanced when the Ag nanoparticles were present in the Y₂O₃:Eu³⁺ luminescent material.     

Photoluminescence and structural characteristics of Lu2O3:Eu nanocrystallites in silica matrix

Two silica ceramics were obtained by mixing nanocrystalline Lu₂O₃:Eu³⁺ with silica sol using the sol-gel technique. The synthesis procedure for both samples differed in the pH of the sol and time of the sol condensation before substrates were mixed together, which implied their different optical properties. The first one has the same spectroscopic properties as Lu₂O₃:Eu³⁺ nanocrystallites with an exception of small lowering of the charge transfer (CT) band intensity. This feature is preserved up to about 950 °C. Above this temperature, nanocrystallites of Lu₂O₃:Eu³⁺ react with the silica matrix synthesis pyrosilicate (Lu₂Si₂O₇). The Eu³⁺ ions occupy only one crystallographic site in the crystal lattice for low concentration of the activator (1%) and two sites for higher concentration (10%). The second sample exhibits different Eu³⁺ emission than Lu₂O₃:Eu³⁺ nanocrystallites and, additionally, a broad band of the matrix originating at the green region of the spectrum. Sintering the sample at higher temperatures leads to disappearance of this broad emission and continuous changes of the Eu³⁺ emission because of the progressive conversion of the Lu₂O₃:Eu³⁺ to pyrosilicate. At 1300 °C for both samples, the reaction of synthesis lutetium pyrosilicate is completed. Structural characteristic of the samples is presented and correlate with the decay profile of the Eu³⁺ emission.     

Gd2O3:Eu@mSiO2核壳双功能纳米棒的制备及性质

通过水热法和正硅酸乙酯水解法制备了一种新颖的Gd2O3:Eu@mSiO2核壳双功能(荧光和介孔)纳米棒。用扫描电镜(SEM)、透射电镜(TEM)、X射线粉末衍射(XRD)、红外光谱(FTIR)等多种测试手段对样品的形貌、物相结构进行分析表征。结果表明,该核壳结构纳米材料以Gd2O3:Eu纳米棒(长~400 nm,直径~100 nm)为核,介孔SiO2为壳,尺寸均匀,分散性良好。荧光光谱表明,在紫外光激发下,核壳纳米棒发射强烈的橙红色荧光。同时该核壳纳米棒能成功标记NCI-H460肺癌细胞。以布洛芬(IBU)为药物模型研究核壳纳米棒的药物负载和释放行为,结果表明,Gd2O3:Eu@mSiO2核壳纳米棒对IBU的负载量可达10.25%,而且其具有明显的缓释效果。IBU负载的样品(IBU-Gd2O3:Eu3+@mSiO2)在紫外光照射下仍呈现Eu3+的橙红色发光,且Eu3+在载药系统中的发光强度随IBU释放量的变化而变化,因此通过发光强度的变化可以跟踪和监测药物及其释放情况。     

溶剂极性对微波辐射老化制备前驱体及CuO/ZnO/Al2O3催化剂结构的影响

在制备CuO/ZnO/Al2O3催化剂的老化过程中,采用微波辐射老化技术,着重研究了溶剂极性对前躯体物相组成,烧后CuO/ZnO/Al2O3催化剂结构及其在浆态床合成甲醇工艺中催化性能的影响。通过XRD、DTG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂表征表明,沉淀母液在微波辐射条件下进行老化,溶剂的极性对前躯体物相组成及催化剂结构影响显著。随着溶剂极性的增大,Zn2+/Cu2+取代Cu2(CO3)(OH)2/Zn5(CO3)2(OH)6中Cu2+/Zn2+的取代反应增强,使得前躯体中(Cu,Zn)5(CO3)2(OH)6和(Cu,Zn)2(CO3)(OH)2物相的含量增多,结晶度提高,导致烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用增强,且CuO晶粒减小,表面Cu含量增加,催化剂活性和稳定性提高。水溶剂的极性最大,制备的催化剂活性和稳定性最好,甲醇的时空收率(STY)和平均失活率分别为320 mg.g-1.h-1和0.11%.d-1。     

Magnetic properties of EuLn2O4 (Ln=rare earths)

Ternary rare earth oxides EuLn₂O₄ (Ln=Gd, Dy-Lu) were prepared. They crystallized in an orthorhombic CaFe₂O₄-type structure with space group Pnma. ¹⁵¹Eu Mössbauer spectroscopic measurements show that the Eu ions are in the divalent state. All these compounds show an antiferromagnetic transition at 4.2-6.3 K. From the positive Weiss constant and the saturation of magnetization for EuLu₂O₄, it is considered that ferromagnetic chains of Eu²⁺ are aligned along the b-axis of the orthorhombic unit cell, with neighboring Eu²⁺ chains antiparallel. When Ln=Gd-Tm, ferromagnetically aligned Eu²⁺ ions interact with the Ln³⁺ ions, which would overcome the magnetic frustration of triangularly aligned Ln³⁺ ions and the EuLn₂O₄ compounds show a simple antiferromagnetic behavior.     

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na₃La₂(BO₃)₃ (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb³⁺ and Eu³⁺)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb³⁺, Eu³⁺) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu³⁺ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to ⁵D₀-⁷F₂ transition of Eu³⁺. The luminescence indicates that the local symmetry of Eu³⁺ in NLBO crystal lattice has no inversion center. Optimum Eu³⁺ concentration of NLBO:Eu³⁺ under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb³⁺ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb³⁺ and Eu³⁺) was analyzed. The relative high quenching concentration was also discussed.     

Synthesis and spectral properties of Eu-doped YF3 nanobundles

YF₃:Eu³⁺ nanobundles were synthesized by a facile microemulsion method. Analysis of X-ray diffraction, scanning electron microscope, and transmission electron microscopy reveals that each nanobundle consists of numerous nanowhiskers with a mean length of ∼500 nm and a mean diameter of ∼2 nm. Under 393-nm excitation, the luminescence was dominated by ⁵D₀ → ⁷F₁ transition, indicating the inversion symmetry of Eu³⁺ site. The luminescence intensity increased with increasing Eu³⁺ concentration, up to about 30 mol%, and then decreased abruptly. The peak positions and spectral shapes of emissions were independent of Eu³⁺ concentration. Finally, the critical distance of energy transfer was calculated.     

Rietveld refinement and photoluminescent properties of a new blue-emitting material: Eu activated SrZnP2O7

A new efficient blue phosphor, Eu²⁺ activated SrZnP₂O₇, has been synthesized at 1000 °C under reduced atmosphere and the crystal structure and photoluminescence properties have been investigated. The crystal structure of SrZnP₂O₇ was obtained via Rietveld refinement of powder X-ray diffraction (XRD) pattern. It was found that SrZnP₂O₇ crystallizes in space group of P2₁/n (no. 14), Z=4, and the unit cell dimensions are: a=5.30906(2) Å, b=8.21392(3) Å, c=12.73595(5) Å, β=90.1573(3)°, and V=555.390(3) Å³. Under ultraviolet excitation (200-400 nm), efficient Eu²⁺ emission peaked at 420 nm was observed, of which the luminescent efficiency at the optimal concentration of Eu²⁺ (4 mol%) was estimated to be 96% as that of BaMgAl₁₀O₁₇:Eu²⁺. Hence, the SrZnP₂O₇:Eu²⁺ exhibit great potential as a phosphor in different applications, such as ultraviolet light emitting diode and photo-therapy lamps.     

Preparation and photoluminescence property of a loose powder, Ca3Al2O6:Eu by calcination of a layered double hydroxide precursor

A novel red light-emitting material, Ca₃Al₂O₆:Eu³⁺, which is the first example found in the Ca₃Al₂O₆ host, was prepared by calcination of a layered double hydroxide precursor at 1350 °C. The precursor, [Ca_2.9−xAl₂Eu_x(OH)_9.8](NO₃)_2+x·2.5H₂O, was prepared by coprecipitation of metal nitrates with sodium hydroxide. The material is a loose powder composed of irregular particles formed from aggregation of particles of a few nanometers, as shown in scanning electron microscope (SEM) images. It was found that the photoluminescence intensity reached the maximum when the calcination temperature was 1350 °C and the concentration of Eu³⁺ was 1.0%. The material emits bright red emission at 614 nm under a radiation of λ=250 nm.     

Thermoluminescence and synchrotron radiation studies on the persistent luminescence of BaAl2O4:Eu,Dy

The persistent luminescence materials, barium aluminates doped with Eu²⁺ and Dy³⁺ (BaAl₂O₄:Eu²⁺,Dy³⁺), were prepared with the combustion synthesis at temperatures between 400 and 600 °C as well as with the solid state reaction at 1500 °C. The concentrations of Eu²⁺/Dy³⁺ (in mol% of the Ba amount) ranged from 0.1/0.1 to 1.0/3.0. The electronic and defect energy level structures were studied with thermoluminescence (TL) and synchrotron radiation (SR) spectroscopies: UV-VUV excitation and emission, as well as with X-ray absorption near-edge structure (XANES) methods. Theoretical calculations using the density functional theory (DFT) were carried out in order to compare with the experimental data.     

Fabrication and luminescent properties of rare earths-doped Gd2(WO4)3 thin film phosphors by Pechini sol-gel process

Rare earth ions (Eu³⁺ and Dy³⁺)-doped Gd₂(WO₄)₃ phosphor films were prepared by a Pechini sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting powders and films. The results of XRD indicate that the films begin to crystallize at 600°C and the crystallinity increases with the elevation of annealing temperatures. The film is uniform and crack-free, mainly consists of closely packed fine particles with an average grain size of 80 nm. Owing to an energy transfer from WO₄²⁻ groups, the rare earth ions show their characteristic emissions in crystalline Gd₂(WO₄)₃ phosphor films, i.e., (J=0, 1, 2, 3; J′=0, 1, 2, 3, 4, not in all cases) transitions for Eu³⁺ and (J=13/2, 15/2) transitions for Dy³⁺, with the hypersensitive transitions (Eu³⁺) and (Dy³⁺) being the most prominent groups, respectively. Both the lifetimes and PL intensity of the Eu³⁺ () and Dy³⁺ () increase with increasing the annealing temperature from 500°C to 800°C, and the optimum doping concentrations for Eu³⁺ and Dy³⁺ are determined to be 30 and 6 at% of Gd³⁺ in Gd₂(WO₄)₃ film host lattices, respectively.     

Homogeneous one-dimensional structured Tb(OH)3:Eu nanorods: Hydrothermal synthesis, energy transfer, and tunable luminescence properties

Nearly monodisperse, homogeneous and well-defined one-dimensional Tb_(1−x)(OH)₃:xEu³⁺ (x=0-3 mol%) nanorods have been prepared through hydrothermal method. The size of the Tb(OH)₃:Eu³⁺ rods could be modulated from nano- to micro-scale by using different amount of ammonia solution. They present highly crystallinity in spite of the moderate reaction temperature. Under ultraviolet excitation into the f→f transition of Tb³⁺ at 382 nm, Tb(OH)₃ samples show the characteristic emission of Tb³⁺ corresponding to ⁵D₄→⁷F_{6, 5, 4, 3} transitions; whereas Tb(OH)₃:Eu³⁺ samples mainly exhibit the characteristic emission of Eu³⁺ corresponding to ⁵D₀→⁷F_{1, 2, 4} transitions due to an efficient energy transfer occurs from Tb³⁺ to Eu³⁺. The increase of Eu³⁺ concentration leads to the increase of the energy transfer efficiency from Tb³⁺ to Eu³⁺. The PL colors of Tb(OH)₃:xEu³⁺ phosphors can be easily tuned from green, yellow, orange, to red by changing the doping concentration (x) of Eu³⁺.     

Neutron diffraction studies of Gd2Zr2O7 pyrochlore

The structure of Gd₂Zr₂O₇ pyrochlore over the temperature range 4-300 K has been refined from powder neutron diffraction data. The sample was enriched in ¹⁶⁰Gd to avoid the high neutron absorption of naturally occurring Gd. The diffraction pattern showed well resolved superlattice reflections indicative of the pyrochlore structure and no evidence is found for anion-disorder from the structural refinements.     

Alpha-particle-induced luminescence of rare-earth-doped Y2O3 nanophosphors

The feasibility of utilizing Y₂O₃:Tb³⁺ and Y₂O₃:Eu³⁺ as radioluminescent nanophosphors under alpha-particle excitation is investigated. Materials synthesized by the urea homogeneous precipitation method were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The XRD analysis of as-produced precipitates and nanophosphors fired at temperatures ranging from 950 to 1100 °C indicated the presence of highly crystalline cubic Y₂O₃ with crystallite sizes of ∼40 nm. SEM and TEM analysis revealed that particles with average diameters of ∼200 nm and comprised of ∼40 nm grains were obtained. High-resolution radioluminescence and photoluminescence spectra were used to investigate the unwanted radioluminescence saturation effects associated with the high ionization rate of alpha-particles. Additionally, the radioluminescence intensity as a function of rare-earth ion dopant concentration is investigated for these materials under alpha-particle excitation. The prospect for utilizing these materials as intermediate absorbers in indirect-conversion radioisotope batteries is discussed.     

Synthesis,Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

The Eu³⁺-doped La₂Zr₂O₇ phosphor with rod-like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X-ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to charac-terize its structure and morphology as well as luminescent properties. The results indicated that the red-emitting phosphor La₂Zr₂O₇:Eu³⁺ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as-obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50-700 nm. The pos-sible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La₂Zr₂O₇:Eu³⁺ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive ⁵DO_→⁷F2 _{electric dipole transition of Eu³⁺ ions. Meanwhile, it was more interesting to note that the emission of ⁵D}1_→⁷FJ _{(J=0, 1, 2) transitions and the splitting patterns of ⁵D}0_→⁷FJ _{(J=1, 2, 4) transitions of Eu³⁺ ions can be observed in the luminescent spectra of La2Zr2O7:Eu³⁺. It was demonstrated that Eu³⁺ preferred to occupy a low symmetry site.}