Luminescence properties of sol-gel derived silica gels doped and undoped with RE-complexes(RE=Eu,Tb)

The luminescence properties of silica gels and silica gels doped with two rare earth complexes,Eu(TTA)3 and Tb(o-CBA)3 (TTA=thenoyltrifluocetate,o-CBA=o-chlorobenzoic acid) are reported and discussed.Pure silica gels show a blue luminescence,and the maximum excitation and emission wavelengths depend strongly on the solvents used.Both of the studied rare earth complexes exhibit the characteristic emissions of the rare earth ions in silica gels,i.e.,Eu3+5 Do→7 FJ(J=0,1,2,3,4),Tb3+5D4→7FJ(J=3,4,5,6) transitions.Compared with the pure RE-complexes powder,the silica gels doped with RE-complexes show fewer emission lines of the rare earth ions.Furthermore the rare earth ion (Tb3+) presents a longer lifetime (1346μs) in silica gel doped with Tb(o-CBA)3 than in pure Tb(o-CBA)3 powder (744μs).The reasons responsible for these results are discussed in the context.     

Molecular structure of [(trien)Zn(im)Zn(trien)](ClO_4)_3 complex and ESR spectra of its single-crystal doped with [(trien)Cu(im)Zn(trien)l(ClO_4)_3 complex

The crystal structure of the title complex was measured, in which the two zinc atoms with coordination polyhedron of distorted tetragonal pyramid (TP) are bridged by an imidazolate in the apical position of the TP forming a dimer. The isomorphous [(trien)Cu(im)Zn(trien)](ClO4)3·H2O complex was doped in the title complex and the recorded single-crystal ESR spectra by fitting gave two sets of the principal values of g and A tensors, which were assigned to the physically distinct sites of the two magnetically equivalent molecules in the unit cell. Lattice distortion at the Cu(II) ion sites and the bonding parameters of Cu(II) ions are further calculated, and the bonding nature of Cu(II) ions is discussed.     

EFFECTS OF RARE EARTH OXIDE ADDITIVES ON STABILITY OF Ni/Al_2O_3 CATALYSTS FOR METHANE STEAM REFORMING REACTION

The stability and the high temperature steam resistance of Ni/Al2O3 catalysis added with rare earth oxides were investigated. It was found that the addition of rare earth oxides resulted in great improvement in the stability and high temperature steam resistance of the catalysts through suppressing the growth of Ni crystallite, the oxidation of metal Ni and the formation of NiAl2O4.     

Hydrothermal synthesis and fluorescence of YF3: Eu3+

<正>Europium(Ⅲ)-doped YF_3 is prepared by a hydrothermal process at 200℃.X-ray diffraction(XRD) pattern identifies the formation of YF_3 phase without detectable impurity.Environment scanning electron microscopy(ESEM) image shows the even size distribution of the samples with cubic morphology.The excitation and emission spectra of the rare earth ions doped YF_3 are investigated by fluorescence spectrophotometer.The excitation spectrum for 591 nm emission has several excitation bands at 320, 365,386,397 and 467 nm,and the main peak value was 397 nm.Typical Eu~(3+) emission peaks at 591 nm(~5D_0→~7F_1) and 612 nm (~5D_0→~7F_2) are observed when excited by 397 nm,and the strongest emission is 591 nm,demonstrating that the rare earth ions occupy the centrosymmetrical sites in YF_3.     

Impact of surface coating on morphological,optical and photoluminescence properties of YF_3:Tb~(3+) nanoparticles

A simple polyol and sol–gel Stober process were employed for synthesis of YF_3:Tb~+(core), YF_3:Tb~+@LaF_3(core/shell) and YF_3:Tb~+@LaF_3@SiO_2(core/shell/SiO_2) nanoparticles(NPs). The phase purity, crystalinity,morphology, optical and photoluminescence properties were investigated and discussed with the help of various analytical techniques including X-ray diffraction pattern,FE-transmission electron microscopy(TEM),FTIR, UV/vis absorption, energy band gap and emission spectra. XRD andFE-TEM studies indicate the formation of core/shell nanostructure and ~10 nm thick amorphous silica surface coating surrounding the core-NPs, which is also confirmed byFTIR spectral results. The surface modifications of core-NPs significantly affect the optical features in the form of energy band gap, which were correlated with particle size of the nanomaterials. The comparative emission spectral results show that after inert layer coating the luminescent core-NPs display stronger emission intensity in respect to core and silica coated core/shell/SiO_2-NPs. The solubility character along with colloidal stability was improved after silica surface modification, whereas luminescent intensity was suppressed causing the surface functionalized with high energy silanol(Si-OH) molecules. These novel luminescent nanomaterials with enhanced emission intensity and excellent solubility in aqueous solvents would be potentially useful for fluorescence bioimaging/optical bio-probe etc.     

Coumarin Modified Rhodamine Derivative： Fluorescent Chemosensor Selectively Recognizing Al^3＋ and Ca^2＋

A fluorescent probe with a coumarin moiety bound to rhodamine 6G hydrazide（l） was synthesized. Its sensing behavior toward various metal ions was investigated with fluorescence methods. Compound I displays different fluorescence emission responses to Al^3＋ and Ca^2＋ at the same excitation wavelength in the visible light region, while no changes occur after the addition of other metal ions. The binding ratios of the complexs of 1-Al^3＋ and 1-Ca^2＋ are both 2：1 according to the Job plot and high resolution mass spectrometer（HRMS） experiments. Moreover, emission spectrum of 1-Ca^2＋ complex and absorption spectrum of the rbodamine dyes overlap largely. When Al^3＋ was added to the 1-Ca2＋ system, calcium in complex 1-Ca2＋ can be displaced by Al^3＋, resulting in the output of another ratiometric sensing signal, which demonstrates that the 1-Ca^2＋ complex can be served as a new and effective fluorescence resonance energy transfer（FRET） donor for rhodamine derivatives.     

The Adsorption of Methanol Vapors on Silica Gel Si-100 and Its Surface Containing Different Concentrations of Chemically Bonded Fluoride Ions

Synthesis of two types Si-100 silica gel with different concentrations of chemically bonded surface fluoride ions (2 and 4 μmol m⁻² ) was performed. Using gravimetric methods, adsorption isotherms of methanol as a function of its pressure in gas phase were measured for these adsorbents. It was found the strong surface deactivation of silica gel in relation to methanol with the increase of bonded fluoride ions concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

用水热法在氧化铝陶瓷膜管上原位合成丝光沸石膜

The mordenite membrane was prepared on a α-Al 2O 3 tube by in situ hydrothermal synthesis. The crystallization was carried out at 443 K for 2～4 days. Silica sol and sodium aluminate were used as the sources of silica and alumina, respectively, and tetraethylammonium bromide (TEABr) as the template. The molar composition of the parent solution was 11 4Na 2O∶1 0Al 2O 3∶40SiO 2∶2500H 2O∶1 5TEABr. SEM and XRD were used to characterize the powder product and the composite membrane. The synthesized mordenite membrane proved to be in a full coverage and an excellent intergrowth. The mordenite crystals were about 20～30 μm and the thickness of the mordenite membrane was 30～40 μm. Based on the SEM pictures of the membrane in the early stage of hydrothermal synthesis, a growth model for the mordenite membrane was assumed. At first a gel layer was formed on the surface of the alumina tube. Nucleation took place in the gel layer but not at the interface of the gel layer and bulk solution. The gel layer provided the nutrients for the growth of zeolite crystals. After the gel layer was consumed completely, the zeolite crystals or membrane were exposed to the bulk solution. The membrane separation test on the mordenite membrane showed that the permeances of pure H 2 and N 2 at 298 K were 6 92×10 -7 and 1 81×10 -7 mol/(m 2·s·Pa), respectively. The ideal selectivity of H 2/N 2 was 3 82, which is higher than that of Knudsen mechanism. It suggested that the mordenite membrane had the ability of molecular sieving.     

Thin Layer Chromatographic Study of Bauxite and Quantitative Estimation of Co-Existing Al3+, Fe2+ and Ti4

 Thin layer chromatography in combination with spectrophotometry and titrimetry has been used to evaluate chromatographic characteristics of bauxite constituents. The retention behaviors of four major constituents (Al3+, Fe2+, Ti4+, Si4+) in bauxite mineral have been examined on plain and modified layers of silica gel G, silica gel H and cellulose with mobile phases containing aqueous sodium chloride, formic acid and hydrochloric acid. Ternary separation of Al-Fe-Ti was achieved on chromatographic plates made of silica gel H. The pH effect and presence of impurity elements in samples, nature of stationary phases on the ternary separation and detection limits of bauxite constituents were studied. Silicon in bauxite was detected on cellulose plates. Quantitative determinations of Al3+, Fe2+ and Ti4+ on silica gel H impregnated with sodium formate layers were achieved by titrimetry and spectrophotometry.     

Preparation and Enantioseparation Property of Chiral Stationary Phases Based on Cellulose Tris(3,5-dimethylbenzoate)——A New Way to Prepare Polysaccharide-coating Type Chiral Stationary Phases

A new method to prepare polysaccharide-coating type chiral stationary phases （CSPs） was developed in this work. As a typical example, naked silica gel was coated by cellulose, which was then derivatized with 3,5-dimethylbenzoyl chloride to afford cellulose tris（3,5-dimethylbenzoate）-silica gel （CTDBS） complex. The silanols on CTDBS were end-capped with 3- aminopropyltriethoxysilane to obtain CSP 1. The amino groups on CSP 1 were further end-capped with 3,5-dimethylbenzoyl chloride to give CSP 2. The silanols on CTDBS were end-capped with methyltrimethoxysilane to yield CSP 3. CSPs 1-3 were characterized by FTIR, solid-state 13C-NMR and elemental analysis. The enantioseparation abilities of CSPs 1-3 were evaluated with structurally various chiral analytes. The enantioseparation results demonstrated that the end-capping moieties on CSPs 1 and 2 significantly affected enantioseparation. In addition, the effect of the structures of chiral analytes and end- capping moieties on the retention factors and the resolutions was discussed.     

增强掺Tb凝胶玻璃荧光性能的有机螯合体的选择

采用原位合成技术, 用溶胶凝胶法制备了稀土离子(Tb^3＋), β-二酮及协同体共掺的二氧化硅玻璃, 测量了它们发射光谱和红外光谱, 并进行了XRD, SEM和TG-DSC测试. 探讨各不同成分原位合成稀土有机配合物在二氧化硅玻璃中的发光性能及热处理温度对发光性能的影响. 结果表明, 在凝胶玻璃中掺入能级较匹配的β-二酮, 可以使稀土离子的荧光增强; 合适的协同体的引用也能使稀土离子的荧光增强. 这些结果为今后制备荧光较强的含Tb离子的SiO₂凝胶玻璃提供了一定的依据.     

In‐situ Synthesis and Photoluminescence of a Europium Porphyrin Complex Incorporated in the Silica Matrix

A practicable synthesis method is explored to synthesize a europium porphyrin complex in which a water‐soluble positively charged 5,10,15,20‐tetrakis(4‐trimethylammoniophenyl)porphyrin iodide, H₂TMePPI, is immobilized into the sol‐gel silica matrix and then in‐situ metallized with the Eu³⁺ ion. The product is characterized by means of the solid UV diffusion reflection spectra, fluorescence spectra, and thermal gravimetric analysis (TG). The solid UV diffusion reflection spectra show that the number of Q bands in the product is less than that of the H₂TMePPI ligand, which is one of the important characteristics of porphyrin metallization. The fluorescence spectra of the product are different from that of the silica doped with free Eu³⁺ ions, implying the different function of Eu³⁺ ions in the product. The TG curves show that the thermal stability of the Eu(III)TMePPI entrapped into silica is higher than that of the H₂TMePPI. The effect of a heat treatment and an UV‐light irradiation on the photoluminescence properties of the composite is investigated in details. The stronger interaction between Eu(III)TMePPI and SiO₂ in the composite is responsible for the different spectra.     

Lumineszenz und sensibilisierte Emission der dreiwertigen Seltenen Erden in Sr3La2W2O12

By activation of the new host lattice Sr₃La₂W₂O₁₂ with the trivalent rare earth ions Nd, Eu, Ho, Er, Tm, Yb an intense emission in the visible and/or infrared region is obtained. Energy transfer from Er³⁺ to Tm³⁺ and Nd³⁺ to Yb³⁺ has been found to occur. The excitation, emission, and diffuse reflectance spectra are analyzed for Sr₃La₂W₂O₁₂: Ln³⁺ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb).     

Calorimetric investigations of luminescent films polycarbonate (PC) doped with europium complex [Eu(TTA)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>]

Polymers doped with rare earth complexes are advantaged in film production for many applications in the luminescent field. In this luminescent polycarbonate (PC) films doped with diaquatris(thenoyltrifluoroacetonate)europium(III) complex [Eu(TTA)₃(H₂O)₂] were prepared and their calorimetric and luminescent properties in the solid state are reported. The thermal behavior was investigated by utilization of differential scanning calorimetry (DSC) and thermogravimetry (TG). Due of the addition of rare earth [Eu(TTA)₃(H₂O)₂] into PC matrix, changes were observed in the thermal behavior concerning the glass transition and thermal stability. Characteristic broadened narrow bands arising from the ⁵D₀ → ⁷F_J transitions (J = 4−0) of Eu³⁺ ion indicate the incorporation of the Eu³⁺ ions in the polymer. The luminescent films show enhancement emission intensity with an increase of rare earth concentration in polymeric matrix accompanied by decrease in thermal stability.     

Site‐Selective Occupancy of Eu2+ Toward Blue‐Light‐Excited Red Emission in a Rb3YSi2O7:Eu Phosphor

Establishing an effective design principle in solid‐state materials for a blue‐light‐excited Eu²⁺‐doped red‐emitting oxide‐based phosphors remains one of the significant challenges for white light‐emitting diodes (WLEDs). Selective occupation of Eu²⁺ in inorganic polyhedra with small coordination numbers results in broad‐band red emission as a result of enhanced crystal‐field splitting of 5d levels. Rb₃YSi₂O₇:Eu exhibits a broad emission band at λ_max=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu²⁺ ions preferably occupy RbO₆ and YO₆ polyhedra and show the characteristic red emission band of Eu²⁺. The excellent thermal quenching resistance, high color‐rendering index R_a (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare‐earth phosphors is an effective strategy to target tailored optical performance.     

Synthesis and Characterization of Polymers Containing Rare Earth Metals

Europium and terbium salts of methacrylic acid (MA) and octanoic acid (OCA) were prepared by a method similar to that described in the literature. Either Eu(MA)₃ or Tb(MA)₃ with three double bonds (C?C) was used as a crosslinker containing rare earth metal ions, but the octanoic acid salts were used as additives. The salts were dissolved in methacrylic acid (<20%) and then copolymerized with methyl methacrylate (>80%) using AIBN (0.2 wt%) as initiator. The two types of polymers, one containing Eu(MA)₃ or Tb(MA)₃ and the other with Eu(OCA)₃ or Tb(OCA)₃, were synthesized by bulk copolymerization in molds made of two glass plates and characterized. The fluorescence spectroscopy of these polymers under ultraviolet/visible excitation light was investigated. The fluorescence excitation and emission spectra of the polymers showed the characteristic spectra of the free Eu³⁺ or Tb³⁺. The fluorescence intensity of the rare earth metal ions increased with increasing rare earth metal content. Fluorescence measurements for Eu(MA)₃, Tb(MA)₃, and Eu(OCA)₃ polymers do not display fluorescence quenching behavior within the range of the rare earth metal content used in our experiments. But for Tb(OCA)₃ polymers, this phenomenon was observed, illustrating that ionic aggregates exist in Tb(OCA)₃ polymeric systems.     

Development of the FTIR properties of nano-structure silica gel doped with different rare earth elements,prepared by sol-gel route

Structural characteristics of pure silica gel (silica-xerogel, SiO₂) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr³⁺, and Europium Eu³⁺, Erbium Er³⁺ and Holmium Ho³⁺ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique, Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications. Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples, based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are obtained for the pure samples at 1100°C and even by doping with the four REEs ions.     

Enhancement of the Up-conversion Luminescence of 12CaO · 7Al2O3:Tm3+/Yb3+ Doped with Alkaline Earth Metal Ions

12CaO?·?7Al₂O₃ doped with lanthanide is characterized by remarkable and technologically important up-conversion emission. However, the low up-conversion efficiency still remains the main limitation for practical applications. To improve the efficiency, bivalent alkaline earth ions (Mg²⁺, Sr²⁺, Ba²⁺)-tridoped Tm³⁺/Yb³⁺/12CaO?·?7Al₂O₃ were synthesized through a high-temperature solid-state reaction. The up-conversion luminescence properties of the samples were investigated by X-ray diffraction, fluorescence spectral measurement pump power, and fluorescence decay curves. The luminescence intensity of samples was significantly enhanced by bivalent alkaline earth ions. 12CaO?·?7Al₂O₃ doped with Sr²⁺ ions has stronger effects on up-conversion enhancement, which is better than Mg²⁺ and Ba²⁺. The up-conversion emission intensity was enhanced by 318 times and the red emission intensity by 218 times with 10?mol% Sr²⁺ ion. Additionally, the blue and red up-conversion emission peaks at 475 and 650?nm corresponding to energy transitions of ¹G₄ → ³H₆ and ¹G₄ → ³F₄, ³F₂ → ³H₆ were characterized using steady-state rate equations.     

Sol–gel synthesis of Eu<Superscript>3+</Superscript>: Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> nanophosphor

Eu (0.1, 0.5 and 1.0 mol%) doped Tb₃Al₅O₁₂ (TAG) was prepared by sol–gel technique through nitrate-citrate route followed by sintering in air (1,100 °C maximum temperature). XRD analysis showed that Eu³⁺ enters the TAG lattice substitutionally replacing the Tb³⁺ ion. Both XRD as well as FTIR investigation showed improvement in crystalline phase with the increase in the sintering temperature. SEM and TEM analysis showed that the powder contains the particles in 5–20 nm size with almost spherical morphology. The excitation spectrum recorded in 300–500 nm showed dominant absorption due to Tb³⁺ while the emission spectra recorded with 380 nm excitation had strong red emission characteristic of Eu³⁺. The intensity of this emission increases with the increase of the Eu concentration from 0.1 to 0.5 mol%. However, the emission intensity decreased on further increase in Eu concentration to 1.0 mol%. This intensity variation with dopant concentration is attributed to well-known “concentration quenching” observed in rare-earth doped materials. Reasonably strong red emission due to Eu was observed when excited with the blue (480 nm) radiation of a Xe lamp indicating the usefulness of the material for the realization of white light LED.