Highly enhanced luminescence of SrB4O7:Eu phosphor prepared by the combustion method using glycine as fuel

Eu²⁺ ion doped into SrB₄O₇ matrix was prepared by combustion method heated at 900 °C in air, using urea (U) or glycine (G) as fuels in different ratios (U100, A10, A25, G10, G25, G75, and G100). In some compositions, ammonium acetate (AA) was used to reduce the exothermicity of combustion reaction. X-ray diffraction and luminescence spectroscopy were used to characterize the material. The high intense emission band at 367 nm is assigned to 4f⁶5d → 4f⁷(⁸S_7/2) transition arisen from divalent europium ion. It is observed that the interconfigurational transition is dependent on the molar ratio of glycine:urea fuels. Glycine fuel favors Eu²⁺ formation in SrB₄O₇ host lattice prepared by combustion method.     

Single step synthesis of Ce doped CaAl2O4 and CaAl4O7 systems

Both CaAl₂O₄ (CA2) and CaAl₄O₇ (CA4) oxide-systems possess monoclinic crystal structure. Herein, we have prepared CA2 and CA4 systems via single step combustion route. A good correlation is observed between calculated and the standard lattice parameters. Ce³⁺ ions were deliberately doped as extrinsic impurities in order to understand the crystal symmetry effects on the emission characteristics in the as-prepared matrices. Large red-shift was observed in CA4-emission spectrum despite of their same crystal structures. Possible reasons are discussed.     

Influence of fuels on the morphology of undoped Y3Al5O12 and photoluminescence of Y3Al5O12:Eu prepared by a combustion method

Undoped and Eu-doped yttrium aluminum garnet nano-powders were prepared by a facile combustion method with citric acid/ethylene diamine tetraacetic acid (EDTA) as fuels and nitrates as oxidizers. The precursors and powders calcined at 1030 °C were investigated using thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. It was found that the powders could be indexed with a garnet structure. The grains were in shape of hemispherical with sizes between 60 nm and 100 nm. With decreasing the citric acid/EDTA ratio, the crystallite size decreased steadily and the specific surface area increased. Investigations of photoluminescence (PL) revealed that as-synthesized YAG:Eu³⁺ phosphor samples exhibited an orange emission band with a main peak at 591 nm under the excitation of 394 nm. As citric acid amounts increased, the quality of crystallinity became higher and the luminescent properties were monotonously enhanced.     

Synthesis of CaAl2O4:Eu,Nd long persistent phosphor by combustion processes and its optical properties

Eu²⁺,Nd³⁺ co-doped calcium aluminate with high brightness and long persistent luminescence was prepared by the combustion method. The luminescent properties of CaAl₂O₄-based luminescent materials have been studied systematically. The phosphor powders were further investigated by X-ray diffractometer (XRD), photoluminescence excitation and emission spectra (PL) and brightness meter. The analytical results indicated that the phase of CaAl₂O₄ was formed when the initiating combustion temperature was 400 °C. The broad band UV excited luminescence of the CaAl₂O₄:Eu²⁺,Nd³⁺ was observed at the blue region (λ_max = 440 nm) due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. The decay time of the persistence indicated that the persistent luminescence phosphor has bright phosphorescence and maintains a long duration.     

Synthesis and characterization of Ba2YSbO6 nanoparticles through a modified combustion process

Nanoparticles of Yttrium Barium Antimonate (Ba₂YSbO₆), a complex perovskite ceramic oxide have been synthesized using an auto ignition combustion process for the first time. The particle size and properties of the nanocrystals have been characterized by X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba₂YSbO₆ and has a complex cubic perovskite (A₂BB'O₆) crystalline structure with lattice constant a = 8.402 Å. Transmission electron microscopy study has shown that the particle size of the as-prepared powder was in the range 20-50 nm. The nanocrystals of Ba₂YSbO₆ synthesized by the combustion technique could be sintered to 97% of the theoretical density at a temperature of 1550 °C for 4 h. The combustion synthesis has a definite advantage that the phase pure Ba₂YSbO₆ nanopowder could be obtained by a single step process without the need of a calcination step.     

Photoluminescence of Fe2O3 nanoparticles prepared by laser oxidation of Fe catalysts in carbon nanotubes

Iron oxide nanoparticles have been produced on the top surface of aligned multi-walled carbon nanotubes by CO₂ laser processing. They were characterized to be Fe₂O₃ nanoparticles by X-ray photoelectron spectroscopy, X-ray diffraction and high resolution scanning electronic microscopy. Absorption bands in the visible region were found to be redshifted compared with the absorption of Fe₂O₃ nanoparticles prepared by traditional chemical methods. Photoluminescence from these Fe₂O₃ nanoparticles shows a broad emission band in the near infrared region for both excitations at 514 and 633 nm. Particle size is considered to be responsible for the unique optical properties of the Fe₂O₃ nanoparticles.     

The photoluminescence properties of Y2O3:Eu prepared by surfactant assisted co-precipitation-molten salt synthesis

Y₂O₃:Eu³⁺ red phosphors were prepared by surfactant assisted co-precipitation-molten salt synthesis method. The effects of surfactant content and annealing temperature on the structure and luminescence were investigated by X-ray diffraction and fluorescence spectrophotometer. The use of surfactant reduces the impurities on the surface of particles and promotes the reaction. The color purity of as-prepared Y₂O₃:Eu³⁺ red phosphors is improved with the presence of surfactant. In the excitation spectra, two strong bands at 394 and 466 nm are attributed to ⁷F_0,1-⁵L₆, ⁷F_0,1-⁵D₂ transitions of Eu³⁺ ions respectively. With the excitation of 394 or 466 nm, the as-fabricated samples reveal excellent red emission as high as that of samples monitored by 254 nm. Thus, the Y₂O₃:Eu³⁺ is a promising red phosphor for ultraviolet-visible light-emitting diodes.     

Preparation and photoluminescence of Er-doped Al2O3 films by sol-gel method

The 0-1.5 mol% Er³⁺-doped Al₂O₃ films have been prepared on the thermally oxidized SiO₂/Si(100) substrate in the dip-coating process by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with the addition of erbium nitrate [Er(NO₃)₃·5H₂O]. The continuous Er³⁺-doped Al₂O₃ films with the thickness of about 1.2 μm were obtained for nine coating cycles at a sintering temperature of 900 °C. The aggregate size for the Er³⁺-doped Al₂O₃ films increased with increasing the Er³⁺ doping concentration from 0 to 1.5 mol%. The root-mean-square roughness of the films was independent on the Er³⁺ doping, which was about 1.8 nm for the 0-1.5 mol% Er³⁺-doped Al₂O₃ films. The γ-Al₂O₃ phase with a (110) preferred orientation was produced for the Al₂O₃ film. The photoluminescence (PL) spectra of 0.1-1.5 mol% Er³⁺-doped Al₂O₃ films were observed at the measurement temperature of 10 K. There was no significant change for the PL peak intensity with the increase of Er³⁺ doping concentration from 0.1 to 1.5 mol%, and similar full width at half maximum of about 40 nm was detected for the 0.1-1.5 mol% Er³⁺-doped Al₂O₃ thin films. The Er³⁺-doped Al₂O₃ films possess the available PL properties for use in planar optical waveguides.     

Synthesis and photoluminescence of nano-Y2O3:Eu phosphors

We report nano-Y₂O₃:Eu³⁺ phosphors with particle size of about 50 nm and relatively high photoluminescence (PL) intensity which is close to the standard for application. The influences of the dope amount, the surfactant and the precipitation pH on the PL intensity, the particle size and the dispersion have been studied. It has been found that 4% is the best Eu³⁺ molar concentration to get the highest PL intensity for both nano- and micro-Y₂O₃:Eu³⁺. The addition of butanol as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH rises, the PL intensity and the particle size increase due to the formation of oxygen bridge bonds.     

纳米Gd2O3:Tb3+荧光粉的微乳液法合成及其光致发光性质

利用TX-100/正己醇/正辛烷/水微乳液法合成纳米Gd2O3Tb3+荧光粉,结构表征证实其为单相的氧化钆,掺杂对晶型无影响,粒子大小较均匀,分散性好,较少团聚.TG-DTA测量了Gd2O3Tb3+的晶型最终形成温度为590℃,发射光谱显示出Tb3+的4个特征发射.随着纳米粒子粒径的减少,发光强度逐渐减弱.     

Synthesis and photoluminescence properties of MgAl2O4:Mn hexagonal nanoplates

MgAl₂O₄:Mn²⁺ hexagonal nanoplates have been synthesized via a simple two-step method. The nanoplates have uniform hexagonal morphology with an average edge length of 1 μm and thickness of 30 nm. X-ray diffraction and various microscopic techniques indicate that MgAl₂O₄:Mn²⁺ nanoplates are single-crystal with multilayered morphology. The formation mechanism has also been discussed. Photoluminescence (PL) spectrum of the MgAl₂O₄:Mn²⁺ nanoplate shows a broad green emission band centered at 568 nm, which is assigned to the ⁴T₁ → ⁶A₁ transition of Mn²⁺ ion. The MgAl₂O₄:Mn²⁺ nanoplate is a promising candidate for efficient nanoscale optical material.     

Preparation and studies of Eu and Tb co-doped Gd2O3 and Y2O3 sol-gel scintillating films

Eu³⁺ (2.5 at.%) and Tb³⁺ (0.005-0.01 at.%) co-doped gadolinium and yttrium oxide (Gd₂O₃ and Y₂O₃) powders and films have been prepared using the sol-gel process. High density and optical quality thin films were prepared with the dip-coating technique. Gadolinium (III) 2,4-pentadionate and yttrium (III) 2,4-pentadionate were used as precursors, and europium and terbium in their nitrate forms were used as doping agents. Chemical and structural analyses (infrared spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy) were conducted on both sol-gel precursor powders and dip-coated films. The morphology of thin films heat-treated at 700 °C was studied by means of atomic force microscopy. It was shown that the highly dense and very smooth films had a root mean roughness (RMS) of 2 nm ± 0.2 (A = 0.0075 Tb³⁺) and 24 nm ± 3.0 (B = 0.01 Tb³⁺). After treatment at 700 °C, the crystallized films were in the cubic phase and presented a polycrystalline structure made up of randomly oriented crystallites with grain sizes varying from 20 to 60 nm. The X-ray induced emission spectra of Eu³⁺- and Tb³⁺-doped Gd₂O₃ and Y₂O₃ powders showed that Tb³⁺ contents of 0.005, 0.0075 and 0.01 at.% affected their optical properties. Lower Tb³⁺ concentrations (down to 0.005 at.%) in both systems enhanced the light yield.     

Novel 3D octahedral La2Sn2O7:Eu microcrystals: Hydrothermal synthesis and photoluminescence properties

Novel 3D octahedral La₂Sn₂O₇:Eu³⁺ microcrystals with pyrochlore structure have been synthesized via a hydrothermal route at 180 ºC for 36 h. The experimental results revealed that the pH value of the precursor solution not only plays an important role in determining the phase of the as-synthesized products, but also has a significant influence on the morphologies of the samples. High-quality and uniform octahedron with an average size of about 700 nm could be easily obtained at the pH value of 12. The photoluminescence spectra showed that 3D octahedral La₂Sn₂O₇:Eu³⁺ displayed improved luminescence compared with the samples of with other shapes. The growth mechanism of octahedral La₂Sn₂O₇:Eu³⁺ microcrystals was briefly proposed.     

Visible photoluminescence from Er-doped TiO2 nanofibres by electrospinning

Er³⁺-doped TiO₂ nanofibres were fabricated with electrospinning method followed by annealing in air at 420, 600, 800 and 1000 °C, respectively. The obtained nanofibres are relatively straight and have an average diameter of ∼ 75 nm. X-ray diffraction measurements showed that the crystal structure transforms from anatase to rutile phase with the increase of annealing temperature. Visible photoluminescence peaking at 528.1, 566.6 and 669.3 nm is detected which is ascribed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ions and the PL intensities increase with the increase of annealing temperature. Meanwhile at high annealing temperatures, near-infrared photoluminescence peaking at 815 nm due to the defect states associated with Ti³⁺ ions is also found. The strong green photoluminescence of Er³⁺ ions may have potential applications in one-dimensional luminescent nanodevices.     

Preparation of cobalt-zinc ferrite (Co0.8Zn0.2Fe2O4) nanopowder via combustion method and investigation of its magnetic properties

Cobalt-zinc ferrite (Co_0.8Zn_0.2Fe₂O₄) was prepared by combustion method, using cobalt, zinc and iron nitrates. The crystallinity of the as-burnt powder was developed by annealing at 700 °C. Crystalline phase was investigated by XRD. Using Williamson-Hall method, the average crystallite sizes for nanoparticles were determined to be about 27 nm before and 37 nm after annealing, and residual stresses for annealed particles were omitted. The morphology of the annealed sample was investigated by TEM and the mean particle size was determined to be about 30 nm. The final stoichiometry of the sample after annealing showed good agreement with the initial stoichiometry using atomic absorption spectrometry. Magnetic properties of the annealed sample such as saturation magnetization, remanence magnetization, and coercivity measured at room temperature were 70 emu/g, 14 emu/g, and 270 Oe, respectively. The Curie temperature of the sample was determined to be 350 °C using AC-susceptibility technique.     

Synthesis,characterization and photoluminescence properties of (Gd1−x,Eux)2O2SO4 sub-microphosphors by homogeneous precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors were synthesized by homogeneous precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and (NH₂)₂CO (urea) starting materials. Fourier transform infrared spectra show that the precursors with different molar ratios of (NH₂)₂CO to Gd₂(SO₄)₃ (the m value) are mostly composed of gadolinium hydroxyl, carbonate and sulfate groups with some crystal water. X-ray diffraction indicated that the precursor (m = 5) can be transformed into pure Gd₂O₂SO₄ phase after heat treated at 900 °C for 2 h in air. Field emission scanning electron microscope micrographs illustrate that the Gd₂O₂SO₄ phosphor particles (m = 5) are quasi-spherical in shape and well dispersed, with a mean particle size of about 300–500 nm. Photoluminescence spectroscopy reveals that the strongest emission peak for (Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors is located at 618 nm under 270 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 5 mol% and the concentration quenching mechanism is due to the electric dipole–dipole interaction. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions fits with a mono exponential function.     

Preparation and characterization of sol-gel derived Er-Yb codoped SiO2/TiO2 core-shell nanoparticles

The Er³⁺-Yb³⁺ codoped silica/titania core-shell nanoparticles were prepared by hydrolysis of titanium alkoxide precursors in the presence of lanthanide ions via sol-gel method. The structure of the particles was characterized by field emission scanning electron microscopy and transmission electron microscopy. The diameter of the silica core is about 50 nm. The thickness of the titania shell is about 4 nm. A typical doping density of Er³⁺ in the titania shell is 4.51 at.%, and the one of Yb³⁺ is 12.20 at.%. The UV-vis-NIR absorption spectra and the photoluminescence spectra were also investigated.     

Synthesis and photoluminescence properties of SrLu2O4:Eu superfine phosphor

Superfine powder SrLu₂O₄:Eu³⁺ was synthesized with a precursor prepared by an EDTA - sol-gel method at relatively low temperature using metal nitrate and EDTA as starting materials. The heat decomposition mechanism of the precursor, formation process of SrLu₂O₄:Eu³⁺and the properties of the particles were investigated by thermo-gravimetric (TG) - differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) analyses. The results show that pure SrLu₂O₄:Eu³⁺ superfine powder has been produced after the precursor was calcinated at 900 °C for 2 h and has an elliptical shape and an average diameter of 80-100 nm. Upon excitation with 250 nm light, all the SrLu₂O₄:Eu³⁺ powders show red and orange emissions due to the 4f-4f transitions of Eu³⁺ ions. The highest photoluminescence intensity at 610 nm was found at a content of about 6 mol% Eu³⁺. Splitting of the ⁵D₀-⁷F₁ emission transition revealed that the Eu³⁺ ions occupied two nonequivalent sites in the crystallite by substituting Lu³⁺ ions.     

Preparation and photoluminescence properties of Eu-doped Ga2O3 nanorods

GaOOH:Eu³⁺ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga₂O₃:Eu³⁺ were converted from as-prepared GaOOH:Eu³⁺ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu³⁺ powders with different morphologies and - and β-Ga₂:Eu³⁺ inherit the morphology of GaOOH:Eu³⁺ exactly. The photoluminescence characteristics of β-Ga₂O₃:Eu³⁺ were also investigated. Experimental results reveal that the color purity of β-Ga₂O₃:Eu³⁺ nanorods with high aspect ratio is enhanced in comparison with β-Ga₂O₃:Eu³⁺ nanorods with low aspect ratio.     

Synthesis and luminescent properties of ZnNb2O6 nanocrystals for solar cell

The phase formation, morphology and luminescent properties of ZnNb₂O₆ nanocrystals by the sol-gel method were investigated at a lower temperature than that of the traditional solid-state reaction method. The products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), photoluminescence spectroscopy (PL) and absorption spectra. The activation energy of ZnNb₂O₆ grain growth is obtained about 18.4 kJ/mol. The diameters of the nanocrystals are in the range of 20-40 nm. The PL spectra excited at 276 nm have a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectrum of the sample at a calcination temperature of 800 °C has a band gap energy of 3.68 eV.