Sol-gel synthesis and photoluminescence properties of BaSO_4/Y_2O_3:Eu~(3+) core-shell submicrospheres

Europium-doped nanocrystalline Y2O3 phosphor layers were coated on the surface of preformed submicron BaSO4 spheres via the sol-gel process.The obtained BaSO4/Y2O3:Eu3+ core-shell phosphors were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS) and photoluminescence spectra.The results showed that the obtained BaSO4/Y2O3:Eu3+ core-shell phosphors consisted of well-dispersed submicron spherical particles with na...     

Systematic study of Nd~(3+) on structural properties of ZnO nanocomposite for biomedical applications; in-vitro biocompatibility,bioactivity, photoluminescence and antioxidant properties

Owing to the inconformity in ionic radius between Nd~(3+) and Zn~(2+), the successful incorporation of Nd~(3+) ion into the ZnO nanocrystals still remains a great challenge. In the present study various doping ratios containing 1 wt%, 5 wt%, 7 wt% and 10 wt% of Nd~(3+) doped ZnO nanoparticles(Nd/ZnO NPs) were synthesized in which a bio-layer caped the NPs. SEM/EDX analysis was performed on the ZnO and Nd/ZnO NPs. In addition, the as-synthesized NPs were characterized using X-ray diffraction(XRD), dynamic light scattering(DLS), differential reflectance spectroscopy(DRS) and photoluminescence(PL) spectroscopy.The average size of Nd(5 wt%)/ZnO NPs was in the range of 6.22 and 15 e18 nm based on XRD and SEM techniques, respectively. The measured band gap values for pure ZnO and Nd/ZnO NCs with doping ratios of 1 wt%, 5 wt%, 7 wt% and 9 wt% were equal to 3.46, 3.26, 3.05, 3.25 and 3.29, respectively. After inhalation, nanoparticles first interact with lung surfactant system and accordingly their toxic effects will appear on lungs cells such as A549 cell line. The effect of Nd/ZnO NPs to interact by human A549 cell line was evaluated by means of cell viability test. According to cell viability test the concentrations of 0.3 and 0.5 mg/mL of Nd/ZnO NPs induce a low toxicity. The present study shows that these toxic effects of Nd/ZnO NPs can be rectified by capping its surface via the addition of a bio-layer around particles in order to prevent them from interacting A549 cell line.     

Influence of annealing temperature on luminescent properties of Eu~(3+)/V~(5+) co-doped nanocrystalline Gd_2Ti_2O_7 powders

Nanosized Gd2(1-x)Eu2xTi2O7:yV5+ phosphors were prepared via sol-gel method and characterized with X-ray diffraction,Raman spectroscopy,diffuse reflectance spectra and photoluminescence spectra.Their PL properties were investigated as functions of the Eu3+ doping concentration and annealing temperature.The results indicated that the as-prepared samples showed a strong emission of Eu3+ under the irradiation of 303 nm.For Eu3+-doped Gd2Ti2O7,the orange emission at 586 nm was the strongest,which was correspond...     

Sensitizing effect of Nd~(3+) on Tb~(3+) activated ZrP_2O_7 long persistent phosphor materials

The long persistent phosphors of Zr_(0.97)P_2 O_7:0.018 Tb~(3+),0.012 Nd3+with Nd~(3+)as sensitized ions and Tb~(3+)as emission centers were synthesized using high temperature solid state reaction.The crystal structure and defects,excitation and emission spectra,decay curves and thermoluminescence(TL) curves of the phosphors were investigated.The synthesized Zr_(0.97)P_2 O_7:0.018 Tb3+,0.012 Nd3+is essentially in line with the standard card PDF#49-1079.The emission band with main peak at 548 nm exhibits the characteristic transitions of ~5 D_3-~7 F_j(j=5,4) and ~5 D3-~7 F_j(j=6,5,4,3) of Tb~(3+).The analysis of excitation and emission spectra shows that there exists the overlap between the emission peaks of Nd~(3+)at 466 and 485 nm and the excitation of Tb3+at 443 and 485 nm,and the energy transfer from Nd3+to Tb3+plays an important role in the improvement of luminescence properties.The decay curves shows that Zr_(0.97)P_2 O_7:0.018 Tb3+,0.012 Nd3+has longer afterglow time than ZrP_2 O_7 and Zr_(0.982)P_2 O_7:0.018 Tb3+.Additionally,the TL curves indicate that the trap depth at 0.72 eV in Zr_(0.97)P_2 O_7:0.018 Tb~(3+),0.012 Nd3+is to the benefit of the afterglow time.The possible luminescence mechanism of ZrP_2 O_7:Tb~(3+),Nd3+is proposed on the basis of the XPS spectra,EPR spectra,excitation and emission spectra,decay curves,TL curves and the analysis of defect equations.     

Spectroscopic and structural properties of MgAl_2O_4:Nd~(3+) nanopowders and ceramics

The structural and spectroscopic properties of MgAl2O4:1%Nd3+ spinel nanocrystals and ceramics were measured and analyzed. Ceramics were prepared from the above mentioned spinel nanocrystals and undoped commercial spinel powder, using the spark plasma sintering(SPS) method. Properties of the obtained ceramics strongly depended on the SPS conditions. The samples were not homogeneous and possessed defects and pores. The most transparent ceramics had 60% transparency at 1000 nm.     

Enhanced afterglow performance of CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors by co-doping Gd~(3+)

In order to effectively improve the afterglow properties of CaAl_2 O_4:Eu~(2+),Nd~(3+) phosphors,a series of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)phosphors belong to monoclinic CaAl_2 O_4,without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4 f~65 d→4 f~7 transition of Eu~(2+) ions.Doping with appropriate amount of Gd~(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd~(3+) induces the fluorescent quenching.The doping of moderate Gd3+changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.     

Enhanced photocatalytic activity of Gd~(3+) doped TiO_2 and Gd_2O_3 modified TiO_2 prepared via ball milling method

Gd~(3+)/TiO_2 and Gd_2O_3/TiO_2 nanoparticles were prepared by ball milling method.The effects of Gd~(3+)ion and Gd_2O_3 on the structure and optical property of TiO_2 were studied by XRD and UV-vis DRS.Specific surface area was determined by Brunauer-Emmett-Teller(BET)method.The morphology and elemental composition were characterized by SEM-EDS.XPS was used to determine the surface compositions and chemical character of elements.The sample sizes and microstructures were observed by TEM.The photocatalytic activities of TiO_2 nanoparticles modified with rare earth metal gadolinium(Gd~(3+)ion or Gd_2O_3)were evaluated by degradation of methylene blue(MB)under UV light.Experimental results indicate that 2,5 mol%Gd~(3+)/TiO_2 shows the best photocatalytic activity compared with Gd_2O_3/TiO_2 and pure TiO_2.The existence of gadolinium can exhibit the aggregation and induce lattice distortion of TiO_2 obtained from XRD,SEM and TEM results.The band gap energy of 2.5 mol%Gd~(3+)/TiO_2 decreases to3.07 eV and it leads to visible light absorption response which can be seen from UV-vis absorption spectra.The surface area of 2.5 mol%Gd~(3+)/TiO_2 equals to 85.8 m~2/g and average crystal size is 21.1 nm.EDS and XPS analyses reveal that gadolinium can be introduced either into TiO_2 lattice or adsorbed on the surface of TiO_2.The content of surface OH groups in 2.5 mol%Gd~(3+)/TiO_2 is 50,88%(1.55 times higher than that of pure TiO_2)and the content of lattice oxygen decreases to 11.26%.The MB(25 mg/L)degradation reaction rate constants of 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2 were0.0713,0.0588 and 0.0263 min~(-1),respectively.The degradation rates of rhodamine B(30 mg/L)in 60 min are 97,9%,90.1%and 84.6%for 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2,respectively.     

Photoluminescence properties of Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5Y_9F_(32)single crystal with high thermal stability for white light-emitting diodes

A novel Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes.The fluorescence spectra of various Sm~(3+)ion concentrations and fixed 0.4 mol% Tm~(3+) and 0.5 mol% Tb~(3+) were measured and studied systematically excited by near-ultraviolet light of 355 nm.The Sm3+ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands.A near pure white light emission with color coordinates(0.3295,0.3057) and color temperature(5657 K) can be obtained when the concentrations of Tm~(3+),Tb~(3+) and Sm~(3+) ions are 0.4 mol%,0.5 mol%and 0.8 mol%,respectively.Furthermore,the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%.The tri-doped Na_5 Y_9 F_(32) single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by～3% with the increase of temperature from 280 to 450 K.The present results demonstrate that the Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal may provide a promising candidate for white light-emitting diodes,luminescent materials and fluorescent display devices.     

A series of Er~(3+)-activated SrLaGa_3O_7 single crystal fibers for mid-infrared laser application

A multidisciplinary approach for the production and characterization of a series of high concentration Er3+activated SrLaGa3 O7(abbreviated as Er:SLGO)crystal fibers is shown to have a great promise for implementation in mid-infrared laser applications.The current approach includes the design and formation of unique layered tetrahedral network structures with several kinds of rare earth(RE)ions including Er ions distributing statistically between layers,such as Er:SLGO,Er,Nd:SLGO,Er,Yb,Ho:SLGO,Er,Eu:SLGO and Er,Ho:SLGO.Five kinds of Er:SLGO crystal fibers were designed to grow via a micropulling down method.Spectroscopic analyses show that Er,Yb,Ho:SLGO and Nd,Er:SLGO crystal fibers were superiorly endowed with inhomogeneous broadening absorption and strong emission.The unique structural components design enables the generation of improved absorption and emission recombination,and the inhibition of self-termination as well.Generally,the use of structural components design may warrant high-efficiency emissions in RE-doped crystal fibers.     

Influence of Y~(3+),Yb~(3+),Gd~(3+) cations on structural and electromagnetic properties of CuFe_2O_4 nanoferrites prepared via one step sol-gel method

Rare earths(REs) play a key role in distorting spinel structure by creating some defects at the lattice sites and make them suitable for magnetodielectric applications.In the present study,the nanoferrites of CuRE_(0.02)Fe_(1.98)O_4,where REs=Y~(3+),Yb~(3+),Gd~(3+),were prepared using one step sol-gel method.The prepared samples are copper ferrite(CFO),yttrium doped copper ferrite(Y-CFO),ytterbium doped copper ferrite(Yb-CFO) and gadolinium doped copper ferrite(Gd-CFO),respectively.The single-phase structure of all the REs doped nanoferrites was determined by X-ray diffraction(XRD) analysis.The porosity,agglomerations and grain size of the REs doped copper ferrite were examined using field emission scanning electron microscopy(FESEM) analysis.Fourier transform infrared spectroscopy(FTIR)elaborates the phase formation and environmental effects on the REs doped nanoparticles(NPs).The recorded room temperature M-H loops from a vibrating sample magnetometer(VSM) elucidate the magnetic properties of the REs doped spinel nanoferrites.The magnetic saturation(M_s) was calculated in the range of 23.08 to 51.78 emu/g.The calculated coercivity values(272.6 to 705.60 Oe) confirm the soft magnetic behavior of REs doped copper ferrites.Furthermore,the electromagnetic and dielectric properties were assessed using a Vector network analyzer(VNA) from 1 to 6 GHz.The permeability,permittivity,dielectric tangent loss and electric modulus of the REs doped spinel ferrites illustrate that the prepared NPs may be suitable for microwave and high frequency applications.     

Influence of dispersant on Y_2O_3:Eu~(3+) powders synthesized by combustion method

Y2O3:Eu3+ powders were synthesized by combustion method and the influence of dispersant was investigated.XRD analysis indicated that the particle size increased with a small amount of dispersant firstly and then decreased with a further increase of dispersant.The morphologies of the powders were studied by scanning electron microscopy(SEM) and high-resolution transmission electron microscopy(HRTEM).SEM images revealed that an appropriate amount of dispersant could reduce the agglomeration significantly.Due ...     

Gd_2O_3-Yb_2O_3-Y_2O_3-ZrO_2热障涂层材料及涂层性能研究

使用化学共沉淀法合成了纳米Gd2O3-Yb2O3-Y2O3-ZrO（2GYYZO）粉末,并最终制备了超细晶团聚的多元稀土氧化物掺杂的GYYZO热喷涂粉末,系统的研究了材料及涂层的基本性能,重点研究了材料及涂层的高温稳定性,材料和涂层的高温相稳定性相对传统纳米8YSZ材料明显提高,对高温热处理过程中涂层孔隙收缩、晶粒长大...     

Photoluminescence properties of Eu~(3+)-doped MgAl_2O_4 nanoparticles in various surrounding media

Eu~(3+)-doped MgAl_2O_4 nanoparticles were prepared by modified Pechini method.X-ray diffraction analysis shows pure tetragonal spinel phase without any impurities.The average size of synthesized nanoparticles was determined to be about 50-60 nm using scanning electron microscopy and static light scattering techniques.Emission and excitation spectra as well as lifetimes of MgAl_2O_4:Eu~(3+) nanophosphors were explored in surrounding media with different refractive indexes.Surrounding medium does not affect luminescence bands position,whereas ~5D_0 lifetime monotonically decreases along with increase of medium refractive index.Effect of surrounding media on radiative and nonradiative decay rates,which were calculated using 4f-4f intensity theory,was studied and discussed.Filling factor of prepared nanoparticles is defined using both radiative and observed lifetimes.     

Effect of alkaline metal ions on the photoluminescence properties of Eu~(3+)-doped Ca_3Al_2O_6 phosphors

Ca_3–xAl_2O_6:x Eu~(3+)(0.02≤x≤0.10) and Ca_(2.92)Al_2O_6:0.04Eu~(3+),0.04M~+(M~+=Li~+, Na~+, and K~+) phosphors were prepared by sol-gel method and their photoluminescence properties were investigated. The crystal structure of the annealed Ca_3–xAl_2O_6:x Eu~(3+) and Ca_(2.92)Al_2O_6:0.04Eu~(3+),0.04M~+ phosphors was analyzed with X-ray diffraction(XRD). The size and morphological characteristics of the annealed phosphors were investigated with a field emission scanning electron microscope(FE-SEM). The photoluminescence properties were evaluated with a spectrofluorometer. The phosphors were effectively excited by the light of 396 nm and showed intense red emission at 616 nm, which originated from the 5D_0→7F_2 transition of Eu~(3+). Among the prepared phosphors, the Ca_(2.96)Al_2O_6:0.04Eu~(3+) phosphor showed the strongest emission intensity and the highest color purity. The addition of alkaline metal ions(Li~+, Na~+, and K~+) to Ca_(2.96)Al_2O_6:0.04Eu~(3+) phosphor degraded the emission intensity and color purity.     

Recent progress of energy transfer and luminescence intensity boosting mechanism in Nd~(3+)-sensitized upconversion nanoparticles

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation.Enormous works have been reported about biomedical applications of 980 nm excited and Yb~(3+)-sensitized upconversion nanoparticles.However,980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment,leading to overheating effect that can induce thermal damages of normal cells and tissues.Recently,Nd~(3+)-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect.Even though Nd~(3+)-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb~(3+)-sensitized counterpart,there are several factors that reduce the upconversion luminescence intensity.In this review article,photon energy harvesting and transferring mechanisms in Nd~(3+),Yb~(3+)and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed.Factors that affect upconversion luminescence intensity and quantum yield of Nd~(3+)-sensitized upconversion nanoparticles are also addressed.Besides,some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd~(3+)sensitized upco nversion nanoparticles are tho roughly summarized.Lastly,the future challenges in the area and our perspectives are in sight.     

Optical studies of Y_3(Al,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors obtained by the Pechini method

The Y3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+)(YAGG) nano-phosphors with homogeneous particle-size distribution,low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method.Only slight aggregation of the crystallites occurs after post-annealing at 1100℃.The intense Ce~(3+)bands in the excitation spectra of the Ce~(3+),Cr~(3+),Nd~(3+)co-doped materials monitoring the Cr~(3+) emission at 690 nm indicate energy transfer from Ce~(3+) to Cr~(3+).Weak Nd~(3+) lines are observed,as well.In addition,the emission of Nd~(3+)at 1060 nm with excitation of Ce~(3+) and Cr~(3+) confirms the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.The short average luminescence decay times for the Ce~(3+) emission indicate the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.Eventually,the Y_3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors exhibit persistent luminescence originating from the 4f~3→4f~3 transitions of Nd~(3+) which matches well to the first biological window to be used in bioimaging applications.     

Synthesis and photoluminescent properties of Eu~(3+)/Dy~(3+) doped SrO-Al_2O_3-SiO_2 glass-ceramics

Eu~(3+)/Dy~(3+) single-doped and co-doped 6SrO-3Al_2O_3-91SiO_2 and 12SrO-6Al_2O_3-82SiO_2 glass and glass-ceramics were synthesized successfully by a sol-gel method. The prepared samples were characterized by the X-ray diffraction, high-resolution transmission electron microscopy, photoluminescent spectra and X-ray photoelectron spectroscopy. The effect of annealing temperature, doped ions and matrix component on the structure and the photoluminescent characteristics was systematically studied. The higher temperature was helpful to form nanocrystals and the amount of SrO and Al_2O_3 could better disperse the rare earth ions in matrix at suitable temperature, and both of them could improve the luminescent intensity. Meanwhile, the doped ions could change the luminescent color by single, codoped and energy transfer. The Sr_2SiO_4 nanocrystals were observed in silicates glasses and became larger with the increase of the annealing temperature and the luminous efficiency of rare-earth(RE) ions could be enhanced when the samples changed from glass state to glass-ceramic state. The results indicated that the photoluminescent properties could be changed through controlling the doped ions, annealing temperature and matrix component.     

Synthesis and enhanced photoluminescence properties of red emitting divalent ion (Ca2+) doped Eu:Y2O3 nanophosphors for optoelectronic applications

This work presents the synthesis of Y₂O₃:Eu³⁺,xCa²⁺ (x = 0 mol%, 1 mol%, 3 mol%, 5 mol%, 7 mol%, 9 mol%, 11 mol%) nanophosphors with enhanced photoluminescence properties through a facile solution combustion method for optoelectronic, display, and lighting applications. The X-ray diffraction (XRD) patterns of the proposed nanophosphor reveal its structural properties and crystalline nature. The transmission electron microscope (TEM) results confirm the change in the shape of the particle and aggregation of particles after co-doping with Ca²⁺. Fourier transform infrared spectroscopy (FTIR) and Raman vibrations also confirm the presence of Y–O vibration and subsequently explain the crystalline nature, structural properties, and purity of the samples. All the synthesized nanophosphors samples emit intense red emission at 613 nm (⁵D₀→⁷F₂) under excitation with 235, 394 and 466 nm wavelengths of Eu³⁺ ions. The photoluminescence (PL) emission spectra excited with 235 nm illustrate the highest emission peak with two other emission peaks excited with 466 and 394 nm that is 1.4 times higher than 466 nm and 1.9 times enhanced by 394 nm wavelength, respectively. The emission intensity of Y₂O₃:Eu³⁺,xCa²⁺ (5 mol%) is increased 8-fold as compared to Eu:Y₂O₃. Doping with Ca²⁺ ions enhances the emission intensity of Eu:Y₂O₃ nanophosphors due to an increase in energy transfer in Ca²⁺→Eu³⁺ through asymmetry in the crystal field and by introduction of radiative defect centers through oxygen vacancies in the yttria matrix. It is also observed that the optical band gap and the lifetime of the ⁵D₀ level of Eu³⁺ ions in Y₂O₃:Eu³⁺,xCa²⁺ nanophosphor sample gets changed with a doping concentration of Ca²⁺ ions. Nanophosphor also reveals high thermal stability and quantum yield as estimating activation energy of 0.25 eV and 81%, respectively. CIE, CCT, and color purity values (>98%) show an improved red-emitting nanophosphor in the warm region of light, which makes this material superior with a specific potential application for UV-based white LEDs with security ink, display devices, and various other optoelectronics devices.     

均匀共沉淀法合成纳米Gd_2O_3:Eu粉体及其发光特性

以六次甲基网胺(hexamethylenetetramine,(CH2)6N4,HMT)为沉淀剂,在GdCl3和EuCl3混合溶液中,利用均匀共沉淀法制得了纳米颗粒.结果表明,获得的Gd2O3:Eu纳米颗粒近似为球形,尺寸均匀,平均粒径为100 nm,且每个球形颗粒由平均粒径为20 nm的微晶聚并而成.Gd2O3:Eu荧光粉在波长612 nm的红光发射来自Eu3+的5D0-7F2电偶极跃迁,发光强度随煅烧温度提高而增强,随Eu3+掺杂摩尔分数的提高而增强.Eu3+掺杂摩尔分数超过7%时,发生浓度淬灭,发光强度减弱.     

First-principles study of structure,mechanical and optical properties of La-and Sc-doped Y_2O_3

The electronic,mechanical and optical properties of La-and Sc-doped Y_2O_3 were investigated using firstprinciples calculations.Two doping sites of Sc and La in Y_2O_3 were modeled.The calculated values of the energy of formation show that the most energetically favorable site for a La atom in Y_2O_3 is a d-site Y atom,while for Sc a b-site Y atom is the more stable position.The calculated band gap shows a slight decrease with increasing La or Sc concentration.The calculated results for the mechanical and optical properties of Y_(2-x)R_xO_3(R = Sc or La,0x ≤ 0.1875)show that La-or Sc-doped Y_2O_3 would have enhanced strength,and thus an ability of resisting external shocks,and increased hardness and mechanical toughness.These improved mechanical properties are achieved without sacrificing the optical properties of the doped compounds.So the doping of La or Sc in Y_2O_3 is permissible in the preparation of Y_2O_3 transparent ceramics,of course,doping of La or Sc will benefit the sintering of transparent ceramics.