Interaction of rare earth ions in Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> material

To discuss the function of Eu and Dy and their interaction in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ long afterglow material, the Eu and Dy single doped and their co-doped Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ were prepared. The samples were characterized by X-ray diffraction (XRD), decay curves, photoluminescence (PL), and thermoluminescence (TL). The results indicate that Sr₂MgSi₂O₇: Eu has afterglow properties, and the doping of Eu ion in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ can lower the depth of traps. Eu ion can not only serve as luminescence center, but also produce traps in the matrix, meanwhile, it also exerts certain influences on the traps produced by Dy in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺. The Dy ion can not act as luminescence center but relates to the change of the traps in the Sr₂MgSi₂O₇ matrix.     

Roles of Eu^2＋, Dy^3＋ Ions in Persistent Luminescence of Strontium Aluminates Phosphors

The polycrystalline Eu^2＋ and Dy ^3＋ co-doped strontium aluminates SrAl2O4： Eu^2＋, Dy^3＋ with different compositions were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence were studied and compared. Results show that the doped Eu^2＋ ion in SrAl2O4： Eu^2＋, Dy^3＋ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy^3＋ ion can hardly yield any luminescence under UV-excitation, but effectively enhance the persistent luminescence and thermo-luminescence of SrAl2O4： Eu^2＋. Dy^3＋ co-doping can help form electron traps with appropriate depth due to its suitable electro-negativity, and increase the density and depth of electron traps. Based on above observations, a persistent luminescence mechanism, electron transfer model, is proposed and illustrated.     

Crystallization and luminescence properties of Sm<Superscript>3+</Superscript>-doped SrO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

The Sm³⁺-doped SrO-Al₂O₃-SiO₂ (SAS) glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated by DTA, XRD, SEM and luminescence spectroscopy. The results indicate that the crystal phase precipitated in this system is monocelsian (SrAl₂Si₂O₈) and with the increase of nucleation/crystallization temperature, the crystallite increases from 66 % to 79 %. The Sm³⁺-doped SAS glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm under the excitation of 475 nm blue light which can be assigned to the ⁴G_5/2→⁶ H _j/2 (j=5, 7, 9, 11) transitions of Sm³⁺, respectively. Besides, by increasing the crystallization temperature or the concentration of Sm³⁺, the emission lights of the samples located at 565, 605 and 650 nm are intensified significantly. The present results demonstrate that the Sm³⁺-doped SAS glass-ceramics are promising luminescence materials for white LED devices by fine controlling and combining of these three green, orange and red lights in appropriate proportion.     

Preparation and optical properties of Er<Superscript>3+</Superscript>: Na<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> transparent glass-ceramics

Na₂O-Al₂O₃-SiO₂ glass-ceramics doped with Er³⁺ ions were synthesized by the conventional melt quenching technique at a low melting temperature. The samples were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR scanning spectrophotometry, and fluorescence spectrometry. The results show that the main crystalline phase of glass-ceramics is nepheline.The best heat-treatment process is at 520 °C for 2 h. Because the up-conversion luminescence and near infrared luminescence properties of glass doped with Eu³⁺ are studied in detail.     

Synthesis and luminescence of nano fluorescent powder of Y<Subscript>4</Subscript>Al<Subscript>2</Subscript>O<Subscript>9</Subscript>: Eu<Superscript>3+</Superscript>

Nano fluorescent powder of Y₄Al₂O₉: Eu³⁺ was synthesized by sol-gel method. The XRD shows that the product prepared at 900°C is pure-phase Y₄Al₂O₉: Eu³⁺. The Y₄Al₂O₉ powder is nano-size crystal testified by BF and ED analysis of TEM. The grain diameter of Y₄Al₂O₉ is in the range between 20 and 50nm, and its average is 30 nm. The luminescent spectra show that Eu³⁺ ious occupy two kinds of sites in Y₄Al₂O₉ crystal lattice. One is in the strict inversion center, and the other is in off lying inversion center. When excited with UV light (λ=254nm), Y₄Al₂O₉: Eu³⁺ exhibits an orange emission bond at λ=590 nm due to the⁵D_o→⁷F₁ transition and a red emission band at λ=610 nm due to⁵D_o→⁷F₂ transition. YUAN Xi-ming: Born in 1951 Funded by Key Scientific and Technological Project of Hubei Province (2001 AA102A03)     

Combustion synthesis and luminescent properties of CaO: Eu<Superscript>3+</Superscript>, M<Superscript>+</Superscript> (M=Li,Na, K) phosphor

Li⁺, Na⁺, or K⁺ co-doped CaO: Eu³⁺ phosphors were prepared by the combustion synthesis method and characterized by X-ray diffraction (XRD), photoluminescence and photoluminescence excitation (PL-PLE) spectra. The experimental results show that, upon excitation with 250 nm xenon light, the emission spectrum of the CaO: Eu³⁺ consists of 4f-4f emission transitions from the ⁵ D ₀ excited level to the ⁷ F _J (J=1, 2, 3) levels with the mainly electric dipole transition ⁵ D ₀→⁷ F ₂ of Eu³⁺, indicating that the Eu³⁺ occupies a low symmetry. The charge-transfer band (CTB) shows somewhat red shift with the decreasing ionic radii of co-doped alkali metal ions. The PL and PLE intensities are significantly enhanced, especially the strongest intensity of luminescent is CaO: Eu³⁺, Li⁺ phosphor, when alkali metal ions are incorporated. The strongest peak of emission is slightly shifted from 614 to 593 nm, indicating that the Eu³⁺ ion locates in a symmetric position (O _h ) when alkali metal ions are incorporated.     

Synthesis of M (M=Co<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>/Ni<Superscript>2+</Superscript>)-doped FeS<Subscript>2</Subscript> Nanospheres with Enhanced Visible-light-induced Photocatalytic Activity

Nano-spherical Co²⁺-doped FeS₂ was synthesized through a simple solvothermal method. The products were investigated using XRD, FE-SEM, BET, ICP, EDS, TEM, HRTEM, XPS, and UV-vis spectroscopy. The results indicated that Co²⁺ ion could change the particle nucleation process and inhibited the particle growth of FeS₂. In addition, when the content of doped Co²⁺ was 15%, the degradation efficiency of methylene blue (MB) achieved 60.72% after 210 min irradiation, which increased by 52.01% than that of the undoped FeS₂. Moreover, comparison experiments also demonstrated that the M (M=Co²⁺, Co²⁺/Ni²⁺)-doped FeS₂ photocatalytic activity efficiency sequence was Co²⁺ > Ni²⁺>Co²⁺/Ni²⁺. This is ascribed to the fact that the Co²⁺ doping could induce the absorption edge shifting into the visible-light region and increased the surface area of the samples. The effect mechanisms of M-doping on the band gap and the photocatalytic activity of FeS₂ were also discussed.     

Preparation and Performance of Si<Superscript>4+</Superscript>-doping Rod-shaped TiO<Subscript>2</Subscript> Powder by Nonhydrolytic Sol-gel Method

Titania (TiO₂) nanorod powder was prepared by nonhydrolytic sol-gel method using titanic chloride (TiCl₄) as titanium source, methylene dichloride (CH₂Cl₂) as solvent, absolute ethyl alcohol (CH₃CH₂OH) as oxygen donor. The effects of Si⁴⁺ doping on the TiO₂ nanocrystalline phase transformation temperature were systematically researched. The results showed that when the molar ratio of Ti⁴⁺ to Si⁴⁺ is 1 to1.3, TiO₂ prepared by calcination at 1100 °C for 1 hour exhibits rod shape and has good photocatalytic activity. Doping of Si⁴⁺ makes glass phase core-shell structure forming on the surface of anatase crystal particles, which can inhibit crystal phase transformation and raise the transformation temperature, making TiO₂ stable in anatase phase at 1200 °C.     

Microstructures and fatigue-free properties of the La<Superscript>3+</Superscript> and Nd<Superscript>3+</Superscript> doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by modified sol-gel technique

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were fabricated on Pt/TiO₂/SiO₂/Si (100) substrates by a modified sol-gel technique. X-ray diffraction indicated that these films were of single phase with random polycrystalline orientations. The surface morphologies of the films were observed by scanning electron microscope, showing uniform, dense films with grain size of 50–100 nm. Well-saturated hysteresis loops of the films were obtained in metal-ferroelectric-metal type capacitors with Cu top electrodes at an applied voltage of 400 kV/cm, giving the remanent polarization (2P _r) and coercive field (2E _c) values of the films of 25.1 μC/cm² and 203 kV/cm for BLT, and 44.2 μC/cm² and 296 kV/cm for BNT, respectively. Moreover, these capacitors did not show fatigue behaviors after up to 1.75×10¹⁰ switching cycles at the test frequency of 1 MHz, suggesting a fatigue-free character. The influences of the La³⁺ and Nd³⁺ doping on the properties of the films were comparatively discussed. Supported by the National Key Basic Research and Development Program of China (Grant No. 2006CB932305) and the Natural Science Foundation of Hubei Province, China (Grant No. 2004ABA082)     

Phase structure and electrical properties of La<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped BiInO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ceramics with high curie temperature

The phase structure and electrical properties of pure and La2O3-doped Bi-InO3-PbTiO3 （BI-PT） ceramics were studied respectively. In （1 -x）BI-xPT （x=0.72-0.80） ceramics, the stability of tetragonal phase increased with increasing x, and pure perovskite structure was obtained for x=-0.80 ceramics. The phase transition temperature range was between 575 ℃ and 600 ℃ for x=0.72-0.80 ceramics, higher than that of PT （-490 ℃）. The c/a ratio almost linearly decreased with increasing La2O3 content in x-0.80 ceramics. It is believed that Pb^2＋ vacancies were formed by La^3＋ substituting Pb^2＋ in La2O3-doped BI-PT ceramics. Tc shifted to lower temperature by 30 ℃/mol% La2O3. The maximum dielectric constant 8557 around 559 ℃ was exhibited in 0.5mol%-doped BI-0.80PT ceramics. La2O3-doped ceramics could be poled resulting from decreasing of c/a ratio and improving of dielectric loss and resistivity. The maximum piezoelectric coefficient d33 was 12 pC/N for 2mol%-doped BI-0.80PT ceramics.     

Fluorescence detection for H<Subscript>2</Subscript>PO<Subscript>4</Subscript><Superscript>-</Superscript> based on carbon dots/Fe<Superscript>3+</Superscript> composite

A novel fluorescent probe for H₂PO₄ ^- was designed and fabricated based on the carbon dots/Fe³⁺ composite. The carbon dots were synthesized by an established one-pot hydrothermal method and characterized by transmission electron microscope, X-ray diffractometer, UV-Vis absorption spectrometer and fluorescence spectrophotometer. The carbon dots/Fe³⁺ composite was obtained by aqueous mixing of carbon dots and FeCl₃, and its fluorescence property was characterized by fluorescence spectrophotometer. The fluorescence of carbon dots was quenched by aqueous Fe³⁺ cations, resulting in the low fluorescence intensity of the carbon dots/Fe³⁺ composite. On the other hand, H₂PO₄ ^- reduced the concentration of Fe³⁺ by chemical reaction and enhanced the fluorescence of the carbon dots/Fe³⁺ composite. The Stern-Volmer equation was introduced to describe the relation between the relative fluorescence intensity of the carbon dots/Fe³⁺ composite and the concentration of H₂PO₄ ^-, and a fine linearity (R ²=0.997) was found in the range of H₂PO₄ ^- concentration of 0.4-12 mM.     

Sensitization and intra-molecular energy transfer of Eu<Superscript>3+</Superscript> by Tb<Superscript>3+</Superscript> in Eu-Tb binuclear complexes/PMMA

A series of Eu0.5Tb0.5(TTA)3Phen/PMMA (TTA=thenoyltrifluoroacetone,Phen=phenanthroline) and Eu0.5Tb0.5(TTA)3Dipy/PMMA (Dipy=2,2’-dipyridyl) were prepared by in-situ polymerization.The structures of the composites were characterized by IR spectra and electron spectrum.Photoluminescence properties were investigated by UV-Vis spectra and fluorescence spectra.Meanwhile,the energy transfer models were set up.The results indicated that polymer parts were attached with the rare-earth molecular parts in the composi...     

Frequency up-conversion luminescence properties and mechanism of Tm<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped oxyfluorogermanate glasses

Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·(1.95-x)GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 (x=0.02,0.05,0.08,0.11,0.14,0.17)in mole percent.Intense blue(476 nm),green(524 and 546 nm)and red(658 nm)emissions which identified from the 1G 4 →3H 6 transition of Tm3+and the(2H 11/2 ,4S 3/2 )→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3+,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white l...     

Preparation and Upeonversion Lumineseenee ofNanoerystailine Gd2O3： Er^3＋, Yb^3＋

Nanocrystalline Gd1.77Yb0.2Er0.03O3 samples were prepared by combustion and precipitation methods. Structures and upconversion luminescence properties of samples were studied. The results of XRD show that all samples are cubic structure, the average crystallite size could be calculated as 23 nm and 39 nm, respectively. The lattice constants were obtained. The FT-IR spectra were measured to investigate the vibrational feature of the samples. Upconversion luminescence spectra of samples under 980 nm laser excitation were investigated. The strong red emission of samples were observed, and attributed to 4F9/2→4I152 transitions of Er^3＋ ions, the emission intensity for sample synthesized by precipitation method is stronger compared to that of combustion method. The possible upconversion luminescence mechanisms in nanocrystalline Gd1.77Yb0.2Er0.03O3 were discussed.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@PAM@NTA-Ni<Superscript>2+</Superscript> Magnetic Composite Nanoparticles for Highly Specific Separation of His-tagged Proteins

A facile approach has been developed to synthesize Fe₃O₄@PAM (polyacrylamide) nanoparticles (NPs) with carboxyl groups on the surfaces by copolymerization with acrylamide and acrylic acid in Fe₃O₄ NPs aqueous suspension. Nitrilotriacetic acid (NTA) was conjugated to the magnetic NPs via well-known carboniimide chemistry using EDC and NHS. The Ni²⁺ ions loaded on the surface of NPs provide abundant docking sites for immobilization of His-tagged green fluorescent proteins (His-tagged GFP). The high magnetic property of Fe₃O₄@PAM@NTA-Ni²⁺ allows an easy separation of the NPs from solution under an external magnetic field, with high His-tagged protein binding capacity (42 μg protein/mg of NPs). The NPs can be recycled for at least four times without significant loss of binding capacity to proteins. These materials show great potential to separate His-tagged protein with low-cost purification at industrial scale.     

Optimized photoluminescence of red phosphor K<Subscript>2</Subscript>LiAlF<Subscript>6</Subscript>:Mn<Superscript>4+</Superscript> synthesized by a cation-exchange method

Red phosphor K₂LiAlF₆:Mn⁴⁺ has been synthesized by a cation-exchange method in HF solution. To optimize their optical properties, phosphors were synthesized using different reaction conditions. The K₂LiAlF₆:0.5%Mn⁴⁺ synthesized at 20°C for 4 h shows the highest luminescence intensity. The temperature-dependent emission intensity of the phosphor was investigated, and it was found to exhibit good thermal stability, making it a promising red phosphor candidate for warm WLEDs.     

Structure and properties of Mg-doped SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> Bi-layered compounds

The structure and properties of Mg-doped SrBi4Ti4O15（SBT） were dicussed. Mg substitution into SBT had two possibilities states with the dopant amount variety. Mg cation substituted mostly into Sr^2＋ and the amount proportion was 68.11%.Mg ion will substitute into Ti ion site in perovskite layer when the doping amount increases. Polarization increases sharply when x=0.1 and then decreases becauses of the domain pinning. The Curie temperature of Mg-doped SBT is about 300 ℃ and there is a broad diffuse phase transition near Tc with a flat peak near the Ta of SBT.     

Dielectric tunable properties of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> microwave composite ceramics

BaTi₄O₉-doped Ba_0.6Sr_0.4TiO₃ (BST) composite ceramics were prepared by the conventional solid-state reaction and their structure, dielectric nonlinear characteristics and microwave dielectric properties were investigated. The secondary phase of the orthorhombic structure Ba₄Ti₁₃O₃₀ is formed among BST composite ceramics with the increase of BaTi₄O₉. At the same time, a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix. The degree of frequency dispersion of dielectric permittivity below T _m is increased initially and then decreased with respect to BaTi₄O₉. As the BaTi₄O₉ content increases, the tunability of composite ceramics decreases, while the Q value increases. Interestingly, 70 wt% BaTi₄O₉-doped BST has a tunability ∼4.0% (under 30 kV/cm biasing) versus a permittivity ∼68 and quality factor ∼134.1 (at ∼3.2 GHz). Supported by the Ministry of Science and Technology of China through 973-project (Grant No. 2009CB623302), the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (Grant No.707024), Shanghai Committee of Science and Technology (Grant No. 07DZ22302), and Shanghai Foundation Project under 06JC14070     

Preparation of nanometer Nd<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript> co-doped CaF<Subscript>2</Subscript> powder by coprecipitation-azeotropic distillation technique

The synthesis of Nd³⁺, Y³⁺:CaF₂ nanopowder was conducted by azeotropic distillation method, which effectively dehydrated hydrous CaF₂ and prevented forming hard agglomerates. X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning calorimetries-thermalgravimetry (DSC-TG), Fourier transform infrared spectroscopy (FT-IR) and absorption spectroscopy were performed to characterize the powder properties. The experimental results showed that products obtained by azeotropic distillation were single phased, rather monodispersed, successfully prevented the hard agglomerate formation and effectively removed the residual water inside the as-prepared precipitate than that of the direct drying. The absorption spectra showed a wider and stronger absorption bands around 792 nm, which should be profitable for LD pumping.     

Synthesis and electrochemical properties of Cr-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode materials for lithium-ion batteries

Cr-doped Li₃V₂(PO₄)₃ cathode materials Li₃V_2−x Cr _x (PO₄)₃ were prepared by a carbothermal reduction(CTR) process. The properties of the Cr-doped Li₃V₂(PO₄)₃ were investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM), and electrochemical measurements. Results show that the Cr-doped Li₃V₂(PO₄)₃ has the same monoclinic structure as the undoped Li₃V₂(PO₄)₃, and the particle size of Cr-doped Li₃V₂(PO₄)₃ is smaller than that of the undoped Li₃V₂(PO₄)₃ and the smallest particle size is only about 1 μm. The Cr-doped Li₃V₂(PO₄)₃ samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Cr was that x=0.04 in the Li₃V_2−x Cr _x (PO₄)₃ samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li₃V₂(PO₄)₃ cathode materials are attributed to the addition of Cr³⁺ ion by stabilizing the monoclinic structure. Funded by the Guangxi Natural Science Foundation(No. 0832259) and the National Basic Research Program of China (No. 2007CB613607)