Superacid Catalyst SO42-/ZrO2-La2O3 Prepared by Ultrasonic Co-precipitation and Low Temperature Aging

低温陈化超声波共沉淀法制得SO₄^2-/ZrO^2-La₂O₃前驱体, 经H₂SO₄处理, 在不同温度下焙烧得到纳米晶催化剂SO₄^2-/ZrO^2-La₂O₃;用Hammett指示剂法测定其酸性. 用XRD、BET、TEM、IR和XPS对样品进行表征,其催化活性用醋酸和甘油的酯化反应进行了评价. 结果表明经超声波搅拌和低温(-15 ºC)陈化,650 ºC焙烧4 h得到的固体超强酸表现出较高催化活性.     

Microwave-assisted synthesis of CuO/ZnO and CuO/ZnO/Al2O3 precursors using urea hydrolysis

Binary CuO/ZnO and ternary CuO/ZnO/Al₂O₃ catalysts have been rapidly synthesized in a multimode microwave oven by the homogeneous precipitation of aurichalcite and hydrotalcite-like precursors using urea hydrolysis. For purposes of comparison, the same catalysts were prepared under conventional heating. The corresponding metal nitrates were mixed with various amounts of urea to yield different urea/(ΣM⁺) molar ratios. The precipitation proceeded stepwise, copper being the first metal to be hydrolyzed. It was found that the higher the urea content, the higher the alkalinization of the solution, an effect which favored the precipitation of Zn (II) (the most pH dependent metal), and in turn, the synthesis of aurichalcite and hydrotalcite-like precursors.Microwave-synthesized catalysts presented similar characteristics to those obtained under conventional heating, but in considerably reduced aging times. Microwave radiation proved to be more efficient than conventional heating under harsh conditions of precipitation, i.e., lower molar ratios of urea with respect to the metal cations in the solution.     

Luminescence investigation of red phosphors Ca0.54Sr0.34−1.5xEu0.08Smx(MoO4)y (WO4)1−y for UV-white LED device

Ca_0.54Sr_0.34−1.5xEu_0.08Sm_x(MoO₄)_y (WO₄)_1−y red phosphors were prepared by solid-state reaction using Na⁺ as a charge compensator for light-emitting diodes (LED). The effects of Na⁺ concentration, synthesis temperature, reaction time and Eu³⁺ concentration were studied for the properties of luminescence and crystal structure of red phosphors. The results show that the optimum reaction condition is 6%, 900 °C, 2 h and 8%. The photoluminescence spectra show that red phosphors are effectively excited at 616 nm by 292, 395 and 465 nm. The wavelengths of 465 nm nicely match the widely applied emission wavelengths of blue LED chips.     

Low thermal quenching and high-efficiency Ce, Tb-co-doped Ca3Sc2Si3O12 green phosphor for white light-emitting diodes

Low thermal quenching and high-efficiency Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSSO:Ce³⁺) phosphors with co-doping Tb³⁺ ion were prepared by a solid state method and the properties of these phosphors were investigated. The results showed that co-doping of Tb³⁺ not only enhances the photoluminescence remarkably and decreases the thermal quenching of the phosphor, but also heightens the performances of the LEDs fabricated with the phosphor. A high-efficiency and low color temperature white LED was fabricated with the prepared CSSO:1%Ce³⁺, 0.5%Tb³⁺ and a red phosphor, indicating that CSSO:1%Ce³⁺,0.5%Tb³⁺ phosphor is a suitable green phosphor for the fabrication of high-efficiency white LEDs.     

Synthesis and characterization of wire-like and near-spherical Eu2O3-doped Y2O3 phosphors by solvothermal reaction

Eu₂O₃-doped yttrium oxide (3 mol%) [Y₂O₃:Eu(3 mol%)] with wire-like and near-spherical morphologies were prepared by a solvothermal treatment using water, ethanol, ethylene glycol and glycerol as reaction media followed by calcination. The powders prepared in water and ethanol possessed wire structure, where the powder treated in water showed high aspect ratio and that in ethanol showed low aspect ratio. The powders prepared in ethylene glycol and glycerol possessed well-dispersed near-spherical powders, which showed almost the same level of photoluminescence emission intensity as that of submicron particles prepared without solvothermal treatment.     

Enhancement of photoluminescence in Sr2CeO4 phosphors by doping with non-rare earth impurities

Non-rare earth impurity doped Sr 2 CeO 4:X (X=Zn,Hg,Al,Ag,Cr) phosphors are prepared by using the combustion method.The structural and photoluminescent properties of the as-prepared phosphors are investigated by X-ray diffraction (XRD) and photoluminescence at room temperature.Experimental results show that zinc addition and firing processing can effectively enhance the photoluminescence of Sr 2 CeO 4 phosphors.     

The improvement of moisture resistance and thermal stability of Ca3SiO4Cl2:Eu phosphor coated with SiO2

Green-emitting phosphors Ca₃SiO₄Cl₂:Eu²⁺ were prepared by the high temperature solid-state method. Sol-gel process was adopted to encapsulate the as-prepared phosphors with tetraethylorthosilicate (TEOS) as silicon coating reagent. Fluorescence spectrometer, scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) patterns were employed to characterize the emission spectra, the surface morphologies and the phase structures, respectively. The chemical stability testing was operated by the method of soaking the phosphors in deionized water and roasting them at different temperatures. The results indicated that the surfaces of the green phosphors were evenly coated by SiO₂ and the phase structure of the coated phosphors remained the same as the uncoated samples. The luminance centre of Eu²⁺ did not shift after surface treatment and the luminance intensity of coated phosphors was lower than that of the uncoated samples. The results demonstrated that the water-resistance stability of the coated phosphor was improved to some degree because the pH value and the luminance intensity variation were both smaller than the uncoated phosphor after steeping within the same time. Moreover, the thermal stability of coated phosphors was enhanced obviously compared to the original samples based on the temperature dependent emission spectra measurement.     

Monochromatic blue-green and red emission of rare-earth ions in MgGa2O4 spinel

Pr³⁺-activated blue-green phosphor and Eu³⁺-activated red phosphor hosted in MgGa₂O₄ spinel have been prepared by a gel-assisted high-temperature calcination process, respectively. Both anion and cation vacancies in the host were formed by decreasing the Mg concentration in the reaction source. The induced vacancies provide possibility of the accommodation of the doped rare-earth ions with larger atomic size in the highly symmetrical spinel structure. Due to the efficient energy transfer from the spinel host to the sole 4f sub-level of the doped rare earths, monochromatic emissions with high efficiency can be obtained to allow the phosphors to find applications in solid-state laser device and other phosphors excited under low energy. The corresponding spectroscopic transition mechanism has been proposed in this work.     

Intense blue-emitting Ca5Al8O14: Eu phosphor for mercury free lamp

The calcium aluminates doped with Eu ions, Ca₅Al₈O₁₄: Eu, phosphors are prepared by the combustion method. The formation of crystalline aluminates was confirmed by X-ray diffraction pattern. The prepared phosphors were characterized by SEM, TGA, DTA, particle size analyzer and Photoluminescence (PL) techniques. From the UV-excited luminescence spectra it was found that the Eu ions acts as a luminescent centre with luminescence at the blue (λ _max = 470 nm) region due to 4f ⁶5d ¹ → 4f ⁷ transition. The excitation spectra show the broad band at 355 nm wavelength (λ _em = 470 nm). The excitation 355 nm is a mercury free excitation and therefore Ca₅Al₈O₁₄: Eu may be useful for the solid state lighting phosphor in lamp industry.      

Synthesis and photoluminescent characteristics of Sr2CeO4 phosphors prepared via a microwave-assisted solvothermal process

Blue-light emitting Sr₂CeO₄ phosphors were successfully prepared via a microwave-assisted solvothermal method employing ethylene glycol as a solvent. The formation of Sr₂CeO₄ phase began when the solvothermally derived precursors were heated at 800 °C. With increase in heating temperatures, significantly enhanced excitation and emission intensities were observed because of an increase in the amount of Sr₂CeO₄. Heating at 1200 °C led to a substantial decrease in mission intensity due to thermal decomposition of Sr₂CeO₄ at elevated temperatures. The solvothermally derived Sr₂CeO₄ was found to exhibit higher emission intensity than the solid-state-reaction-derived phosphors. According to the deconvoluted emission spectra, two emission peaks are attributed to two metal-to-ligand charge-transfer states. Based on the deconvoluted results, a qualitative energy-level diagram of Sr₂CeO₄ was proposed. VUV-excited luminescence studies for Sr₂CeO₄ indicate that one peak at 193 nm is assigned to the charge-transfer transition between Sr²⁺ and O²⁻.     

Synthesis and characterization of Sr3Al2O6：Eu2＋, Dy3＋ phosphors prepared by sol-gel-combustion processing

A type of red luminescent Sr3Al2O6:Eu2+, Dy3+ phosphor powder is synthesised by sol-gel-combustion processing, with metal nitrates used as the source of metal ions and citric acid as a chelating agent of metal ions. By tracing the formation process of the sol-gel, it is found that it is necessary to reduce the amount of NO3- by dropping ethanol into the solution for forming a stable and homogeneous sol-gel. Thermogravimetric and Differential Scanning Calorimeter Analysis, x-ray diffractionmeter, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the luminescent properties of the as-synthesised Sr3Al2O6:Eu2+, Dy3+. The results reveal that the Sr3Al2O6 crystallises completely when the combustion ash is sintered at 1250 C. The excitation and the emission spectra indicate that the excitation broadband lies mainly in a visible range and the phosphors emit a strong light at 618 nm under the excitation of 472 nm. The afterglow of (Sr0.94Eu0.03Dy0.03)3Al2O6 phosphors sintered at 1250 ℃ lasts for over 1000 s when the excited source is cut off.     

Low temperature quenching and high efficiency Tm, La or Tb co-doped CaSc2O4:Ce phosphors for light-emitting diodes

Low temperature quenching and high efficiency CaSc₂O₄:Ce³⁺ (CSO:Ce³⁺) phosphors co-doped with Tm³⁺, La³⁺ and Tb³⁺ ions were prepared by a solid state method and the phase-forming, morphology, luminescence and application properties of these phosphors were investigated. The results showed that co-doping of Tm³⁺, La³⁺ and Tb³⁺ ions can improve the luminescence properties and decrease temperature quenching of CSO:Ce³⁺ phosphor remarkably. High efficiency green-light-emitting diodes were fabricated with the prepared phosphors and InGaN blue-emitting (∼460 nm) chips. The good performances of the green-light-emitting LEDs made from co-doped CSO:Ce³⁺ phosphors confirm the luminescence enhancement and indicate that Tm³⁺, La³⁺ and Tb³⁺ co-doped CSO:Ce³⁺ phosphors are suitable candidates for the fabrication of high efficiency white LEDs.     

P掺杂对绿色荧光粉BaMgAl$lt;sub$gt;10$lt;/sub$gt;O$lt;sub$gt;17$lt;/sub$gt;:Mn$lt;sup$gt;2+$lt;/sup$gt;性能的影响

采用高温固相法合成P掺杂的BaMgAl₁₀O₁₇:Mn²⁺荧光粉,其中P通过（NH₄）₂HPO₄引入.利用X射线衍射谱、傅里叶变换红外光谱、扫描电子显微镜、能量色散谱、真空紫外光谱等研究了P掺杂对BaMgAl₁₀O₁₇:Mn²⁺晶体结构、微观形貌、发光性能等的影响.研究结果表明：（NH₄）₂HPO₄具有助熔剂的作用,它的加入有助于荧光粉的晶化,改善荧光粉的形貌.P掺杂进入晶格,使得晶胞参数变小,从而改变了Mn²⁺的晶体场环境,引起发射光谱蓝移,色坐标x值降低.P掺杂能有效提高基质对真空紫外线的吸收,从而提高真空紫外激发下的发光强度. 关键词： P掺杂 10O₁₇:Mn²⁺')" href="#">BaMgAl₁₀O₁₇:Mn²⁺ 晶体结构 真空紫外     

Luminescence in trivalent rare earth activated Sr4Al2O7 phosphor

In this paper we report the combustion synthesis of trivalent rare-earth (RE³⁺ = Dy, Eu and Ce) activated Sr₄Al₂O₇ phosphor. The prepared phosphors were characterized by the X-ray powder diffraction (XRD) and photoluminescence (PL) techniques. Photoluminescence emission peaks of Sr₄Al₂O₇:Dy³⁺ phosphor at 474 nm and 578 nm in the blue and yellow region of the spectrum. The prepared Eu³⁺ doped phosphors were excited by 395 nm then we found that the characteristics emission of europium ions at 615 nm (⁵D₀?⁷F₂) and 592 nm (⁵D₀?⁷F₁). Photoluminescence (PL) peaks situated at wavelengths of 363 and 378 nm in the UV region under excitation at around 326 nm in the Sr₄Al₂O₇:Ce³⁺ phosphor.     

Emission analysis of Pr and Tm: Ca2Gd2W3O14 phosphors

5 mol% of Pr³⁺ and Tm³⁺ ions activated calcium gadolinium tungstate (Ca₂Gd₂W₃O₁₄₎ phosphors were synthesized by traditional solid state reaction method. Crystalline phase structure was identified from the X-ray diffraction (XRD) profiles. From the scanning electron microscopy (SEM) images, we have observed the agglomeration of the particles, and average grain size is around 40-300 nm. Using the energy dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectra, identified the elements and functional groups present in the prepared phosphors. The emission spectrum of Pr³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown an intense red emission at 615 nm with the excitation wavelength λ_exci=450 nm and thus these red color emitting powder phosphors are used as one of the components in the preparation of WLEDs. The excitation spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ powder phosphor has shown a ligand to metal charge transfer (W-O) band (LMCT) within the WO₄²⁻ group. Emission spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ phosphors have shown blue emissions at 453 nm (¹D₂→³F₄).     

Synthesis and properties of Au-Fe3O4 and Ag-Fe3O4 heterodimeric nanoparticles

Monodisperse Au-Fe 3 O 4 heterodimeric nanoparticles (NPs) were prepared by injecting precursors into a hot reaction solution.The size of Au and Fe 3 O 4 particles can be controlled by changing the injection temperature.UV-Vis spectra show that the surface plasma resonance band of Au-Fe 3 O 4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size.The as-prepared heterodimeric Au-Fe 3 O 4 NPs exhibited superparamagnetic properties at room temperature.The Ag-Fe 3 O 4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO 3 as precursor instead of HAuCl 4.It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs.     

Enhanced luminescent properties of long-persistent Sr2MgSi2O7:Eu, Dy phosphor prepared by the co-precipitation method

Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors were prepared by the (aminopropyl)-triethoxysilane (APTES) co-precipitation method. Effects of synthesis temperature on the crystal characteristics, luminescent properties and afterglow performance of Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors have been discussed in detail and compared with the corresponding commercial product. The experimental results indicated that the sample could be synthesized at a relatively lower temperature and had better performance on the above-mentioned properties using the co-precipitation method.     

A novel UV-emitting phosphor: Li6CaB3O8.5:Pb

Pure Li₆CaB₃O_8.5 and Li₆Ca_1−xPb_xB₃O_8.5 (0.005≤x≤0.04) materials were prepared by a solution combustion synthesis method. The phase of synthesized materials was determined using the powder XRD and FTIR. The synthesized materials were investigated using spectrofluorometer at room temperature. The emission and excitation bands of the synthesized phosphors were observed at 307 and 268 nm, respectively. The dependence of the emission intensity on the Pb²⁺ concentration for the Li₆Ca_1−xPb_xB₃O_8.5 (0.005≤x≤0.04) was studied and observed that the optimum concentration of Pb²⁺ in phosphor is 0.01 mol. The Stokes shift of the synthesized phosphor was calculated to be 4740 cm^-1.     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

Sol-gel growth of Gd2MoO6:Eu nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6:Eu) and their luminescent properties

SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors. The XRD results demonstrate that the Gd₂MoO₆:Eu³⁺ layers on the SiO₂ spheres begin to crystallize after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd₂MoO₆:Eu³⁺ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu³⁺ shows a strong PL luminescence (dominated by ⁵D₀-⁷F₂ red emission at 613 nm) under the excitation of 307 nm UV light. The PL intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles.