白光LED用LaPO4:Eu3+红色荧光粉的合成与表征

利用水热法制备了性能稳定的红色荧光粉LaPO4:Eu3+,同时研究了不同的Eu3+浓度、煅烧温度对荧光粉发光性能的影响.通过X射线粉末衍射(XRD)和扫描电子显微镜(SEM)来表征荧光粉的晶体结构和颗粒大小及形貌;用激发光谱和发射光谱以及荧光衰减曲线来表征荧光粉的荧光性能.结果表明:未煅烧时前躯体主要是六方晶相LaPO4·0.5H2O,煅烧温度在900℃时,所制备样品为单斜相LaPO4:Eu3+;SEM图像显示5 at.%Eu3+掺杂LaPO4呈椭球形,颗粒长约为500 nm,宽约为300 nm.最大发射波长和激发波长分别为592 nm和393 nm,发射光谱中592 nm和612 nm的发射峰对应的是Eu3+离子的5D0→7F1和5D0→7F2跃迁.其荧光寿命为3.32 ms.     

Luminescent Properties of Green Phosphor Ca8Mg（SiO4 ）4 Cl2：EU^2＋ , DY^3＋ for LED Applications

The new phosphor calcium magnesium chlorosilicate, codoped with Eu^2＋ and Dy^3＋, was synthesized with the help of the high temperature solid state reaction in reducing atmosphere. The excitation and emission spectra were very similar to that of Ca8Mg（SiO4）4Cl2 ：Eu^2＋, and the Dy^3＋ concentration influenced the emission intensity of this phosphor. The intensity of Eu^2＋ and Dy^3＋ codoped CMSC was stronger than that of Eu^2＋ singly doped CMSC. The emission spectrum of the Dy^3＋ ion overlapped the absorption band of the Eu^2＋ ion, indicating that an energy transfer from Dy^3＋ to Eu^2＋ took place in CMSC：Eu^2＋, Dy^3＋ phosphor. The mechanism of the energy transfer from Dy^3＋ tO Eu^2＋, in this phosphor, might be resonant energy transfer.     

Photocatalytic activity of cerium-doped mesoporous TiO2 coated Fe3O4 magnetic composite under UV and visible light

A novel kind of magnetically separable photocatalyst of cerrium-doped mesoporous titanium dioxide coated magnetite (Ce/MTiO2/ Fe3O4) was prepared and its activities under UV and visible light were reported. The catalysts with Ce/MTiO2 shell and Fe3O4 core were pre-pared by coating photoactive Ce/MTiO2 onto a magnetic Fe3O4 core through the hydrolysis of tetrabutyltitanate (Ti(OBu)4, TBT) with pre-cursors of ammonium ceric nitrate and TBT in the presence of Fe3O4 particles. The MTiO2 shell was for photocatalysis, the Fe3O4 core was for separation by the magnetic field and the doped Ce was used to enhance the photocatalytic activity of MTiO2. The morphological, struc-tural and optical properties of the prepared samples were characterized by Brunauer-Emmett-Teller (BET) surface area, transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The effect of cerrium-doped content on the photocatalytic activity was studied and the result revealed that 0.5 mol.% Ce/MTiO2/Fe3O4 exhibited highest photoactivity. The photocatalytic activities of obtained photocatalysts under UV and visible light were estimated by measuring the degradation rate of methylene blue (MB, 50 mg/L) in an aqueous solution. The results showed that the prepared photocatalyst was activated by visible light and used as effective catalyst in photooxi-dation reactions. In addition, the possibility of cyclic usage of the prepared photocatalyst was also confirmed. Moreover, Ce/MTiO2 was tightly bound to Fe3O4 and could be easily recovered from the medium by an external magnetic filed. So, the photocatalyst can be reused without any mass loss. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Synthesis and characterization of manganese doped CeO2 nanopowders from hydrolysis and oxidation of Ce37Mn18C45

The Mn-doped CeO 2 nanopowders with high catalysis activity were successfully fabricated through a simple hydrolyzed-oxidized approach.Firstly,the alloy Ce 37 Mn 18 C 45 was prepared in vacuum induction melting furnace.Subsequently,Mn-doped CeO 2 nanopowders with 142 m 2 /g of specific surface area were obtained through a simple hydrolyzed-oxidized procedure of the alloy.Those nanopowders were heat treated at different temperatures.The obtained materials were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM) and energy dispersive spectroscopy(EDS).And the catalytic activity on vinyl chloride(VC) emission combustion was investigated.The results showed that those nanopowders after hydrolyzed-oxidized from Ce 37 Mn 18 C 45 mainly consisted of CeO 2 and Mn 3 O 4.Manganese element increased the thermal stability of CeO 2 nanopowders.The Mn-doped CeO 2 nanopowders had three morphologies.Small particles were Mn-doped CeO 2,square particles were Mn 3 O 4 and the rods were Mn 3 O 4 and Mn 2 O 3.The Mn-doped CeO 2 nanopowders had good vinyl chloride(VC) emission catalytic performance.     

Bi_2WO_6 doped with rare earth ions:Preparation,characterization and photocatalytic activity under simulated solar irradiation

Rare-earth modification Bi_2 WO_6 composites(RE/Bi_2 WO_6) were studied by experimental performance and theory computation based on the different 4 f orbits of selected rare earth elements(La,Ce,Gd,and Yb).The prepared RE/Bi_2 WO_6 was characterized by XRD,SEM/TEM,XPS,UV-vis DRS,and N_2 adsorption to learn their physical-chemical properties.Azo dye Rhodamine B(RhB) was photodegraded as a target pollutant to investigate the photocatalytic activity of prepared RE/Bi_2 WO_6 composites.The results of experiment and computation show that four rare earth elements with different electron configurations retain the phase and morphology of Bi_2 WO_6 and enhance the removal efficiency of RhB under simulated solar irradiation.The optimum doping contents are 0.01%,0.05%,0.05% and 0.01% for La-,Ce-,Gd-,and Yb-doped Bi_2 WO_6,respectively.However,light rare earth La and Ce doped composites indicate some difference in visible light adso rption capacity and mineralization on RhB co mpared with heavy rare earth Gd and Yb doped composites.Both La/Bi_2 WO_6 and Ce/Bi_2 WO_6 possess larger pore size and higher mineralization ability than Gd/Bi_2 WO_6 and Yb/Bi_2 WO_6 under the same experimental conditions while Gd/Bi_2 WO_6 and Yb/Bi_2 WO_6 show stronger red shift to the visible light due to the more 4 f electrons.The hole oxidation plays a major role in the photodegradation of RhB by all RE/Bi_2 WO_6.     

Preparation and photocatalytic activity of La^3＋ and Eu^3＋ co-doped TiO2 nanoparticles： photo-assisted degradation of methylene blue

Rare earth ions La³⁺ and Eu³⁺ co-doped TiO₂ photocatalyst (La-Eu/TiO₂) was prepared by sol-gel method, and characterized by various techniques such as X-ray diffraction (XRD), specific surface area and porosity (BET and BJH), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the La-Eu/TiO₂ was evaluated by the degradation of methylene blue (MB) under UV light irradiation. The catalyst had a relatively uniform particle diameter distribution in the range of 40–60 nm. When calcining at 600°C, the XRD patterns of La-Eu/TiO₂ indicated the anatase phase, while the XPS patterns showed the Ti⁴⁺, La³⁺ and Eu³⁺ ions existence. The DRS spectra showed red shift in the band-gap transition. The experimental results of MB degradation demonstrated that the photocatalytic activity of La-Eu/TiO₂ was significantly enhanced due to better separation of photogenerated electron-hole pairs.     

Synthesis and luminescence properties of SrAleO4：Eue＋,Dy3＋ hollow microspheres via a solvothermal co-precipitation method

SrAl2O4:Eu2+,Dy3+ hollow microspheres were successfully prepared through a facile and mild solvothermal co-precipitation combining with a postcalcining process.The structure and particle morphology were investigated by X-ray diffraction(XRD),scanning and transmission electron microscopy(SEM and TEM)pictures,respectively.The mechanism for the formation of spherical SrAl2O4:Eu2+,Dy3+ phosphor was preliminary presented.After being irradiated with ultraviolet(UV)light,the spherical phosphor emitted long-lasting green phosphorescence.Both the photoluminescence(PL)spectra and luminance decay,compared with that of commercial bulky powders,revealed that the phosphors had efficient luminescent and long lasting properties.It was considered that the SrAl2O4:Eu2+,Dy3+ hollow microspheres had promising long-lasting phosphorescence with potential scale-dependent applications in photonic devices.     

Hydrothermal Synthesis of RbLn2F7 and VUV Spectroscopy of RbLn2 F7 ：Eu^3＋（Ln=Gd, Y）

RbLn2F7（Ln = Gd, Y, Er, Yb and Lu）, crystallized in the hexagonal RbEr2F7 structure type, is synthesized by a hydrothermal method. The excitation spectra of Eu^3 ＋ -doped RbGd （Y）2F7 suggest that the oxygen content is very low in the samples obtained by hydrothermal synthesis. Only the f-f transitions of Gd^3＋ ions are observed in the excitation spectrum of RbGd2F7：Eu^3＋ （0.5mol%）, while those of Eu^3＋ ions do not appear. When the Gd^3＋ ions are excited, the absorbed energy is transferred efficiently from Gd^3＋ to Eu^3＋ . The spectra show that the doped Eu^3＋ ions are located in non-centrosymmetric sites in hexagonal RbLn2F7.     

Green,orange, and red upconversion luminescence in Nd^3＋/Yb^3＋： Cs2NaGdCl6 powders under 785 nm laser excitation

Nd^3＋：Cs2NaGdCl6 and Nd^3＋, Yb^3＋：Cs2NaGdCl6 polycrystalline powder samples were prepared by Morss method E. Under 785 nm semiconductor laser pumping, the upconversion luminescence of Nd^3＋ ions in Cs2NaGdCl6 was investigated at room temperature, and three upconversion emissions near 538 nm （Green）, 603 nm （Orange）, and 675 nm （Red） were observed and assigned to ^4G7/2→^4I9/2, （^4G7/2→^4I11/2; ^4G5/2→^4I9/2）, and （^4G7/2→^4I13/2; ^4G5/2→^4I11/2 ）, respectively. The dependences of these upconverted emissions on laser power and Nd^3＋ ion concentration were investigated, to explore the upconversion mechanism. The effect of doping Yb^3＋ ions on the upconversion luminescence of Nd^3＋ in Cs2NaGdCl6 was also studied under 785 nm laser excitation. The energy transfer processes were discussed as the possible mechanism for the above upconversion emissions.     

Synthesis and Upconversion Luminescence of LaF3 ： Yb^3＋ , Er^＋/SiO2 Core/Shell Microcrystals

LaF3：Yb^3＋ , Er^＋ microcrystals were synthesized by a hydrothermal method, and then, the LaF3： Yb^3＋ , Er^＋ microcrystals were coated with silica. Phase identification of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 was performed via XRD. The TEM image showed that the size of LaF3： Yb^3＋ , Er^＋ was 150 nm and LaF3： Yb^3＋ , Er^＋/SiO2 presented clearly a core/shell structure with 20 nm shell thickness. The upconversion spectra of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 in solid state and in ethanol were studied with a 980 nm diode laser as the excitation source. The upconversion spectra showed that the silica shell had little effect on the properties of fluorescence of the LaF3：Yb^3＋ , Er^＋ microcrystals. At the same time, the green luminescence photo of LaF3： Yb3＋, Er3＋/SiO2 in the PBS buffer was obtained, which indicated that the LaF3： Yb^3＋ , Er^＋/SiO2 could be used in biological applications.