Synthesis and Luminescence of MeSiO_3:Eu,Bi Luminophors(Me=Mg,Ca,Sr,Ba)

The luminophors of four kinds of alkaline earth meta-silicates doped with Eu~3 and/or Bi~(3 )ion(s)weresynthesized and the luminescence properties of Bi~(3 )and Eu~(3 )ions were studied.The regularities that Me(Ⅱ)ions affect the luminescence of Eu~(3 )ion sensitized by Bi~(3 )ion were investigated.The optimum composition andsynthesis condition were obtained.The absorption and emission peak are situated at 283 and 353nm with theoptimum concentration 0.02 mol of Bi~(3 )in CaSiO_3:Bi.In CaSiO_3:Bi,the optimum concentration of Bi~(3 )is0.007 mol and that of Eu~(3 )is 0.040 mol.For all of the alkaline earth ions concerned in MeSiO_3:Eu,Bi,theBi~(3 )can sensitize the Eu~(3 )and the Me(Ⅱ)ions in host and make a great difference in the adsorption hand ofBi~(3 )ion.by exciting Bi~(3 )ion,the emissions are from both Eu~(3 )and Bi~(3 )ions and the best sensitization effectis achieved when Me(Ⅱ)is Sr.     

Luminescent Properties of Eu~(3+) and Bi~(3+) and Their Interaction in LaBO_3 and GdBO_3

Under the excitation of UV light and cathode ray,the dependence of the excitation and emission spectraand luminescent lifetime of Eu~(3+)and Bi~(3+)on composition and structure in LABO_3 and GdBO_3 has been stu-died.The results indicate that the emission spectra of Eu~(3+)in LaBO_3 with aragonite structure and in GdBO_3with YBO_3 structure are quite different.Under 254 nm excitation,Eu~(3+)emission is sensitized by Bi~(3+)inGdBO_3 matrix.In other case Eu~(3+)emission is quenched by Bi(3+).     

Upconversion multicolor tuning of NaY(WO4)2:Tb3+ with Eu3+ doping

A series of Tb~(3+) and Eu~(3+) co-doped NaY(WO_4)_2 phosphors were synthesized by hydrothermal reactions.The crystal structure,morphology,upconversion luminescent properties,the energy transfer from Tb~(3+) to Eu~(3+)ions and the ~5 D_4→ ~7 F_5 transition of the Tb~(3+) ion in NaY(WO_4)_2:Tb~(3+),Eu~(3+) phosphors were investigated in details.The results indicate that all the synthesized samples are of pure tetragonal phase NaY(WO_4)2.Furthermore,the micrometer-sized needle spheres and excellent dispersion of the particles are obtained by adding polyethylene glycol(PEG-2000) as the surfactant.Phosphors of NaY(WO_4)_2:Tb~(3+),Eu~(3+) exhibit the492 nm blue emission peak,546 nm green emission peak,595 nm orange emission peak and 616 nm red emission peak under 790 nm excitation.The energy transfer from Tb~(3+) to Eu~(3+) is a resonant transfer,in which electric dipole-dipole interaction plays a leading role.By adjusting the doping concentration of Eu~(3+) in NaY(WO_4)_2: 1.0 mol%Tb~(3+),xmol%Eu~(3+) phosphors,the emitting color of UC phosphors can be tuned from green to red.     

Spectral Structures of Eu~(2 ) in ABF_4 and A_2SiF_6 (A=Na,K,Rb,Cs)

The phosphors of ABF_4:Eu~(2 )and A_2SiF_6:Eu~(2 )(A=Na,K,Rb,Cs)have been synthesized,and thecrystallographic data obtained accord with ASTM.In these materials,the f→f sharp lines emissions of Eu~(2 )were observed.The coordination numbers of Eu~(2 )in both NaBF_4 and Na_2SiF_6 hosts are less than 8.     

Electron Transition of Eu~(2+) and Energy Transfer in Crystals BaFX:Eu~(2+),Eu~(3+) (X=Cl,Br)

In crystals BaFX:Eu~(2+)(X=Cl,Br).there exists configuration interaction between 4f~65d and 4f~65s ex-cited state of Eu~(2+)ion.and it results in the change of relative intensities of d-f and f-f transition.The transition~S_-_2→4f~65d-6s is observed.The variation of F/X atomic ratio between 110/90 and 90/110 does not obvi-ously influence the luminescence of BaFX:Eu~(2-).There is energy transfer between Eu~(2+)(f-f)and Eu~(3+)whichcoexists in the matrices.     

NaY zeolites modified by La3+ and Ba2+:the effect of synthesis details on surface structure and catalytic performance for lactic acid to acrylic acid

Modified NaY zeolites have been widely studied and the modification metal element is normally single, while few researches have been conducted on NaY zeolites modified by two kinds of metals. In our study, a series of La3+ and Ba2+ modified NaY zeolites were synthesized through different impregnation procedures. Lactic acid dehydration to acrylic acid was selected as a probe reaction to test the catalytic performance of these zeolites synthesized. The effects of synthesis details on their pore structures an...     

Photostimulated Luminescence and F-centers of Sr_3Ca_2(PO_4)_3X:Eu~(2+)(X=F,Cl,Br)

This paper reports the F-centers and photostimulated luminescence of Eu~(2+)-activated Sr_3Ca_2(PO_4)_3Xcrystals.The influence of various halide ions on the F-centers and their energy level is discussed.The mechanismfor the photostimulated luminescence and valence change of Eu ion in that process have been investigated.     

Emission Spectra and Crystallographic Sites of Eu~(2+) in Ca_8Zn(SiO_4)_4Cl_2

The fluorescent characteristic and emission spectra of Eu~(2+) in the cubic structureCa_8Zn(SiO_4)_4Cl_2 with three kinds of cation sites is reported.The influence of temperature,Eu~(2+) concentra-tion and excitation conditions on fluorescent properties of Eu~(2+) are studied at 77 and 298 K.Thecoordination number of Eu~(2+) at different sites is obtained.The green and red emission bands arise fromEu_(2+) ions locating on eight- and six- coordinated inequivalent sites respectively.     

Solid State Structure and Lyotropic Mesomorphism of Rare-Earth Trisdode-cylsulphates in the Water-Ethylene Glycol System

The phase behaviour of lanthanide(Ⅲ) dodecylsulphates, Ln(C12H25SO4)3, by thermo-optical microscopy using Lawrence penetration technique was investigated. The lyotropic phase behaviour of lanthanide(Ⅲ) dodecylsulphates in ethylene glycol water in mixtures hereof, depends on the composition of the solvent. For pure ethylene glycol and mixtures of ethylene glycol and water three different mesophases are formed, i.e.a lamellar, a cubic and a hexagonal phase, whereas when water is used as solvent no cubic phase is formed. The size of the lanthanide ion has no influence on the mesomorphism of these metallomesogens, although the smaller the lanthanide ion the lower the solubility.     

Enhancement of luminescence intensity and spectroscopic analysis of Eu3+ activated and Li+ charge-compensated Bi2O3 nanophosphors for solid-state lighting

The present work reports the synthesis, characterization, photoluminescence and photocatalytic activity of Eu~(3+)(1 mol%-11 mol%) doped and Li~+(0.5 mol%-5 mol%) co-doped Bi_2 O_3 nanophosphors(NPs) by sonochemical method. The average particle size was estimated using powder X-ray diffraction(PXRD)and transmission electron microscopy(TEM) and is found to be in the range of 30-35 nm. The scanning electron microscopy(SEM) images were highly dependent on sonication time and concentration of epigallocatechin gallate(EGCG) bio-surfactant. The energy gap of doped and co-doped Bi_2 O_3 nanophosphors was estimated using Kubelka-Munk(K-M) function and is found to be in the range of2.9-3.08 eV. The effect of Li+ co-doping on luminescence of optimized Bi_2 O_3:Eu~(3+) was studied and is found about more than 3 fold enhancement of emission intensity. Judd-Ofelt parameters(Ω_2, Ω_4 and Ω_6).transition probabilities(A_T), quantum efficiency(η), luminescence lifetime(τ_(rad)), color chromaticity coordinates(CIE) and correlated color temperature(CCT) values were estimated from the emission spectra and are discussed in detail. The estimated CIE chromaticity co-ordinates are very close to the NTSC(National Television Standard Committee) standard value of red emission. The synthesized NPs show excellent photocatalytic activity of acid red-88 under UV-light irradiation, which can degrade 98.1% in60 min. The decreasing electron-hole pair recombination rate with quick electron transfer ability is predominantly ascribed to the balance between crystallite size, morphology, band gap, defects, surface area, etc. These results show a light for the use of sonochemical route of Bi_2 O_3:Eu~(3+):Li~+ in solid state display and photocatalytic applications.     

Electroreduction of Y(Ⅲ)in Molten Chlorides and Alloying

The electroreduction of Y(Ⅲ)on tungsten electrode in NaCl-KCl-YCl_3 melt has been investi-gated by cyclic voltammetry.Deposition of Y(Ⅲ)to Y(0)is reversible in one step.The cyclic voltammetry,convolution voltammetry,potential-time curve after potentiostatic electrolysis and X-ray diffraction analy-sis were used to study the electrode process of Y(Ⅲ)reduced on iron electrode.Several Y-Fe intermetalliccompounds are formed before the deposition of metallic yttrium.The diffusion coefficient anddiffusion activation energy of Y in Y_6Fe_(23) were determined by current-time curve at potential step.The results indicate the diffusion of Y in its alloy phase is so slow that this step will control the electrode pro-cess.     

Optical and magnetic properties of GaN epilayers implanted with ytterbium

We have studied the optical and magnetic properties of ytterbium implanted GaN epilayer grown on(0001)sapphire by metalorganic chemical vapor by deposition(MOCVD).Samples were implanted at room temperature with Yb ions at dose 4x1015 cm-2 and energy of 150 keV.The implanted samples were annealed at 1000 ℃ in N2 at atmospheric pressure to recover implantation damages.The photoluminescence (PL),PL excitation(PLE),and PL kinetics have been studied with continuous and pulse photo-excitations in 360-1100 nm spectral range at different temperatures.The characteristic Yb3+ion emission spectra were observed in the spectral range between 970-1050 nm.Theoretical fittings of the experimental PL temperature and PL kinetics data suggest that Yb3+ions are involved in at least two major luminescence centers.The PLE spectra indicate that excitation of the Yb3+ion occurs via electron-hole pair generation and complex processes.Magnetization versus magnetic field curves shows an enhancement of magnetic order for Yb-implanted samples in 5 K to 300 K temperature range.The Yb-implanted GaN sample showing weak ferromagnetic behavior was compared with the ferromagnetic in situ doped GaYbN material.     

Study on Spectral Overlap Model for Energy Transfer between J-Multiplets in Rare Earth-Doped Crystals

Based on the experimental data of KY3F10：Tm3^ reported by Dial, Kushida‘s spectral overlap model (SOM) of energy transfer between J-multiplets was studied. Firstly, with the help of the Inokuti-Hirayama and Yokota-Tanimoto models, the luminescence decay curve of ^3H4 of Tm^3 ion was fitted, and the fitted values of corresponding interaction parameters CDA of energy transfer and CDD of energy migration were obtained. Secondly, by compared with Kushida‘‘s SOM in which the relevant Judd-Ofelt approximative transition rates are known, the average overlap integrals of SOD and SDA were obtained. For S DD, how to treat the contribution of the electronic-dipole (ED) crystal field transition forbidden by C4v site symmetry in the calculation of SDD was discussed. For SDA we suggested that, by including the contribution of the phonon sidebands in the analysis of oscillator strength of transition, Kushida‘‘s SOM of ED-ED resonant energy transfer rate can be extended to non-resonant phonon-assisted D-A energy transfer. The strengths and widths of phonon sidebands in this example were discussed, and the results were reasonably good.     

Enhanced photodegradation activity of ZnO:Eu~(3+)and ZnO:Eu~(3+)@Au 3D hierarchical structures

In this work the flower-like hierarchical structures(HS) based on 3 D pristine ZnO,ZnO:Eu~(3+)and ZnO:Eu~(3+)@Au were successfully obtained by a template-free solvothermal and deposition-precipitation method.The decolorization/photodegradation of these structures towards model organic dye(rhodamine 6 G) was studied.The synthesized ZnO-based HS were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),UV-vis and photoluminescence(PL) spectroscopies.The proposed synthesis approaches allow to obtain highly crystalline 3 D ZnO,ZnO:Eu~(3+) and ZnO:Eu~(3+)@Au composites.Results of scanning microscopy show that ZnO flower-like HS are assemblies from smaller components,forming larger ones,the whole ZnO structure was approximately 3 μm.Au nanoparticles(size～10 nm)are successfully deposited on ZnO HS surface.Luminescent studies show that ZnO is an ideal matrix for incorporation of Eu~(3+)ions in broad concentration range(Eu~(3+)=1.0 at%-5.0 at%) with an efficient red luminescence.The strong UV emission in ZnO,as well as ZnO;Eu~(3+)HS is observed under 325 nm excitation.Doping of ZnO HS matrix by Eu~(3+)ions leads to the red shift of deep level emission peak(DLE).The PL intensity reaches the maximum up to 5 at% Eu~(3+).The photocatalytic properties of ZnO and ZnO:Eu~(3+)@Au HS were investigated under UV-Vis light irradiation towards rhodamine 6 G.The obtained results demonstrate the synergetic effect of the deposited gold nanoparticles and Eu~(3+)doping on photocatalytic activity of ZnO:Eu~(3+)@Au HS in comparison to pristine ZnO and ZnO:Eu~(3+)HS.     

Effects of Rare Earth on Behavior of Precipitation and Properties in Microalloyed Steels

The influence of rare earths on the behavior of precipitation of 14MnNb,X60 and 10Mn V steels was studied by STEM, XRD, ICP and thermal simulation method. The main carbonitride precipitates are Nb(C, N), (Nb, Ti) (C, N) and V(C, N). In austenite RE delays the beginning of precipitation, and decreases the rate of precipitation. In ferrite RE promotes precipitation and increases the amount of equilibrium carbonitride precipitation. RE can make precipitates fine,globular and dispersed in the microalloyed steels. With the increase of the amount of RE in steel, the amount of precipitation increases. The promotion effect is weakened with excessive RE. RE has only little influence on the strength of microalloyed steel, but it can improve impact toughness effectively.     

LUMINESCENCE CENTERS OF Eu~(2 ) IN KCaF_3:Eu~(2 )

The nature of the emission center of Eu~(2 ) in KCaF_3:Eu~(2 ) strongly depends on the preparative condi-tions.Experimental results show that there are two different d→f transition emission bands,and the origin ofthese two emission bands,their interrelationship and the effect of doping concentration on them have been dis-cussed.A Eu~(2 )-Eu~(3 ) valency change process has been proposed.     

Photoluminescence and energy transfer in transparent glass-ceramics based on GdF3:RE3+ (RE = Tb,Eu) nanocrystals

In the present work,the transparent oxyfluoride glass-ceramic samples containing GdF_3:RE~(3+)(RE=Tb,Eu) nanocrystals(nGCs) were fabricated via controlled heat-treatment of precursor xerogels prepared using a sol-gel method.The formation of GdF_3 nanocrystalline phase from gadolinium(III) trifluoroacetate was verified based on XRD measurements.The average crystal sizes calculated from Scherrer formula were estimated to～10 nm as well as～6 nm for Tb~(3+)-and Eu~(3+)-doped samples,respectively.The optical behavior of prepared sol-gel samples was evaluated based on photoluminescence excitation(PLE) and emission spectra(PL) as well as luminescence decay analysis.Obtained samples exhibit the ~5D_4→~7F_J(J=6-3,Tb~(3+))and the ~5D_0→~7F_J(J=0-4,Eu~(3+)) emission bands recorded within the visible spectral area under excitation at near-UV(393 nm(Eu~(3+)),351,369,378 nm(Tb~(3+))) as well as middle-UV illumination(273 nm(Gd~(3+))).Additionally,based on recorded decay curves,the luminescence lifetimes(τ_m) for the ~5D_4(Tb3+) and the ~5D_0(Eu~(3+))excited states were also evaluated.In general,recorded luminescence spectra and double-exponential character of decay curves for nGCs indicate a successful migration of Tb~(3+) and Eu~(3+) dopant ions from amorphous silicate framework to lowphonon energy GdF_3 nanocrystal phase.     

Magnetic Properties and Surface Activity Sites of Pt-Dy/γ-Al_2O_3 Catalysts

The magnetism and surface behaviour of Pt-Dy/γ-Al_2O_3 catalysts were studied respectively bymeans of a Faraday magnetic balance and the method of carbon disulfide.The ferromagnetic impurity in thesupport,γ-Al_2O_3,at low temperature was corrected for the first time.The magnetic susceptibilities of the cat-alysts follow the sequence in different stage of preparation:χ_(uncalcined)<χ_(calcined)<χ_(reduced).The magnetic susceptibilities of the catalysts decrease as they adsorb hydrogen,cyclohexane or benzene.There is a correlation between the aromatization yield of cyclohexane or heptane on these catalysts and themagnetic susceptibility of the catalysts.Since addition of Dy increases the number of adsorption sites and therelevant proportions of weak adsorption sites,the abilities of sulfur-resistance and cyclohexanedehydrogenation are improved.In Pt-Dy/γ-A:_2O_3 catalysts,Dy improves the aromatization activity andstability of the catalyst and plays the role of the electron promoter.     

Solar spectral conversion based on plastic films of lanthanide-doped ionosilicas for photovoltaics:Down-shifting layers and luminescent solar concentrators

The mismatch between the photovoltaic(PV) cells absorption and the solar irradiance on earth is one of the major limitations towards more efficient PV energy conversion.This aspect was addressed by downshifting the solar irradiance on Earth through luminescent down-shifting layers based on lanthanidedoped surface-functionalized ionosilicas(ISs) embedded in poly(methyl methacrylate)(PMMA) coated on the surface of commercial Si-based PV cells.The IS-PMMA hybrid materials exhibit efficient solar radiation harvesting(spectral overlap of ～9.5 × 10~(19) photons/(s·m~2)) and conversion(quantum yield～52%).The direct solar radiation and the down-shifted radiation are partially guided and lost through total internal reflection to the layer edges being unavailable for PV conversion of the coated PV cell.By tuning the down-shifting layer thickness,it also acts as luminescent solar concentrator enabling the collection of the guided radiation by flexible PV cells applied on the borders of the down-shifting layer leading to an enhancement of the PV energy conversion from ～5%(in the case of the single-use of the luminescent down-shifting layer) to～13% comparing with the bare PV cell.The overall electrical output of the device resulted in an absolute external quantum efficiency increase of～32% for the optimized Eu~(3+)-based films in the UV spectral region(compared with the bare PV device,which is among the best values reported so far).     

Neurotoxicity and brain localization of europium doped Gd_2O_3 nanotubes in rats after intranasal instillation

Europium doped Gd_2 O_3 nanotubes(Gd_2 O_3:Eu~(3+) NTs) were synthesized and characterized. Then,the neurotoxicity and brain localization of Gd_2 O_3:Eu~(3+) NTs were evaluated. All experimental rats were administered by intranasal instillation with 30 μL Gd_2 O_3:Eu~(3+) NTs suspension 3.0 and 15.0 mg/mL respectively every other day for 35 consecutive days, and the rats of control group were administered with an equal volume of physiological saline. The Morris water maze was used to assess the rats' spatial learning and memory ability. The oxidative stress-related biomarkers and the activity of AChE in striatum and hippocampus were analyzed, and the histopathology of hippocampus and striatum was observed.The brain localization of gadolinium(Gd) was measured. The results showed that the escape latency of the rats in high-dose group prolonged significantly compared with that of control group after treatment of six weeks(p 0.05), and the swimming time in D quadrant of high-dose group shortened significantly compared with the control group(p 0.01). In addition, high-dose Gd_2 O_3:Eu~(3+) NTs could decrease the activity of GSH-Px and CAT in hippocampus and the activity of SOD in striatum(p 0.05). MDA content in hippocampus and striatum of high-dose group increased(p 0.05). High dose Gd_2 O_3:Eu~(3+) NTs could increase the activity of AChE in hippocampus(p 0.05) and in striatum(p 0.001). But there were no significant differences between the low-dose group and control group(p 0.05). The results of Gd localization in brain showed that the ranking of Gd levels was olfactory bulb striatum hippocampus cerebellum brain stem frontal cortex. The pathology results indicated that high dose Gd_2 O_3:Eu~(3+)NTs resulted in degeneration necrosis, nucleus pycnosis, and axons disappearance of the nerve cells at CA1, CA3 and DG area of hippocampus. Therefore, the results implied that Gd_2 O_3:Eu~(3+) NTs have the potential neurotoxicity and a possible danger in causing neurodegenerative disorders after intranasal instillation.