Optically stimulated luminescence of Dy~(3+)-doped NaCaPO_4 glass-ceramics

Dy~(3+)-doped glass-ceramics containing NaCaPO_4 crystals were successfully fabricated by heat treatment at base glass,and the luminescence properties were investigated for potential applications in radiation measurements.The photo luminescence(PL) excitation and emission spectra exhibit transitions related to Dy~(3+) ions corresponding to the strongest excitation and emission wavelengths at 351 and 575 nm,respectively.The CW-OSL properties as a function of dopant concentration,pre-heating temperature,pre-heating time and signal fading were investigated.The most appropriate Dy~(3+)ion concentration was found to be 0.25 mol%.The TL glow curves have a broad peak feature peaking at 195±5 ℃.The fading of the OSL signal would keep stable in five days with the intensity value of about 76.11%.The samples also exhibit good signal reusability and a broad linear dose response range(0.02-1000 Gy).     

Effect of titanium dioxide and gadolinium dopants on photocatalytic behavior for acriflavine dye

Herein,we report the experimental methodology to optimize the operational parameters of the photocatalytic degradation of acriflavine dye using TiO_2 and Gd~(3+) as dopant.A series of Gd~(3+) doped TiO_2 nanoparticles were synthesized via hydrothermal route and characterized using various techniques like FT-IR,UV,XRD,FESEM and EDS.It is observed that synthesized particles are in the range of 25-30 nm with spherical shape in nature.TiO_2 has rutile phase and the average particle size was estimated from Scherrer's equation.Energy bandgap was estimated using Tauc's plot.The photodegradation was carried out under UV light in pseudofirst order condition.To understand the kinetics,four experimental parameters were chosen as independent variables like percentage of dopant,initial concentration of dye,dosage of catalyst and pH of reaction medium.The degradation efficiency of 92% was observed for 0.5%Gd doped TiO_2 at catalyst dosage of 0.3 g/dm~3,pH 10 and dye concentration of 3×10~(-6) mol/dm~3.It is observed that,the photocatalytic activity of TiO_2 can be increased by using gadolinium as dopant only in optimum concentration.Further,this photocatalyst can be employed to degrade other o rganic pollutants.     

Existence form of lathanum and its improving mechanism of visible-light-driven La-F co-doped TiO_2

The existence form and effect of La on the phase composition,morphology,recombination of photocarriers,and optical absorptivity of La-F codoped TiO_2 were investigated.Experimental results indicate that all the phase composition of samples is anatase TiO_2,the grain sizes decrease with the increasing of La content The catalysts have a well-defined spherical structure with an average size of 12-14 nm,and the doping elements are uniformly dispersed.Compared with pure TiO_2,the absorption edge of La_(1.5)F_5-TiO_2 red shifts from 388 to 437 nm,accordingly the energy gap(E_g) reduces from 32 to 2.84 eV,Besides,the recombination rate of electron-holes in La_(1.5)F_5-TiO_2 is the weakest among the prepared samples,and the specific surface area of La_(1.5)F_5-TiO_2 reaches 105.27 m~2/g.The apparent reaction rate constant k of La_(1.5)F_5-TiO_2 for methylene blue(MB) degradation under visible light obtained from the apparent first-order model achieves 0.0166±0.52 min~(-1),which is greater than 0.0033±0.09 min 1 of TiO_2.Moreover,high-resolution transmission electron microscopy(HRTEM) observation reveals that there coexist La_2O_3 particles in the co-doped TiO_2.     

A comparative study of physicochemical and photocatalytic properties of visible light responsive Fe,Gd and P single and tri-doped TiO2 nanomaterials

High performance Fe-Gd-P tri-doped TiO_2 nanoparticles(1 at% for each dopant) were successfully synthesized by a modified sol-gel method. Various analytical and spectroscopic techniques were carried out to determine the physicochemical properties of the prepared samples, including XRD, EDX, FESEM,BET, FTIR, XPS, PL, EIS and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activities of prepared samples were evaluated by photo degradation of methyl orange(MO) and 4-chlorophenol(4-CP) as model pollutants under visible light irradiation. Effects of each dopant on different properties of TiO_2 nanoparticles were investigated. Results show that Gd and P doping enhances TiO2 surface textural properties by forming Ti-O-Gd and Ti-O-P bonds. It is found that Gd plays a superior role in increasing oxygen vacancies and organic species on TiO_2 surface. Gd doping also facilitates transferring of the photo-induced charge carriers to the surface adsorbed species. The enhanced electronic band structure and visible light response, as well as high electron lifetime of Fe-Gd-P tri-doped sample is mainly attributed to Fe and Gd doping. The tri-doped TiO_2 with rate constant of k_(app)= 1.28 × 10~(-2) min~(-1) for MO and k_(app) = 0.94 × 10~(-2) min~(-1) for 4-CP, shows the highest photodegradation rate among all samples including undoped and single doped samples. The improved photocatalytic performance of Fe-Gd-P tridoped TiO_2 is due to the synergistic effect of enhanced surface chemistry and textural properties,increased number of surface adsorbed hydroxyl groups and organic species, improved visible light absorption, increased lifetime of the photo-induced electron/hole pairs and boosted interfacial charge transfer.     

Enhanced photocatalytic activities of Nd-doped TiO_2 under visible light using a facile sol-gel method

Titanium dioxide nanoparticles modified with neodymium in the range of 1 mol% to 5 mol% were prepared with template-free sol-gel method.The structures of obtained samples were characterized by X-ray powder diffraction analysis.X-ray photoelectron spectroscopy,scanning electron microscopy,transmission electron microscopy and diffuse reflectance spectroscopy.The photocatalytic activity of the obtained samples was evaluated by photodegradation of methyl orange in aqueous solution under ultraviolet-visible(λ 350 nm) and visible(λ 420 nm) irradiation.The experimental results show that the 1 mol% Nd-doped TiO_2 exhibits the highest photocatalytic activity,of which the degradation can reach to 96.5% under visible irradiation.According to the XRD results,the pristine samples are combined with anatase TiO_2 and rutile TiO_2.while the Nd-doped TiO_2 samples are anatase TiO_2 only.This transformation has made an obvious promotion of photocatalyst activity after modification.     

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.     

Effects of annealing temperature and neodymium concentration on structural and photoluminescence properties of Nd~(3+)-doped Y_2O_3-SiO_2 powders

We report the structural and photoluminescence(PL) properties of Nd~(3+)-doped Y_2 O_3-SiO_2 powders(Y_2 O_3-SiO_2:Nd~(3+)) as functions of annealing temperature and Nd~(3+) ion doping concentration.Y_2 O_3-SiO_2:Nd~(3+)powders were prepared using the high-energy ball-milling(HEBM) method,and their structural and PL properties were investigated using X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,and PL spectroscopy.The XRD results reveal a cubic phase without impurities,and the peak broadening decreases with an increase in annealing temperature due to the increase in the crystallite size.The PL emission intensity increases with an increase in annealing temperature.The highest PL emission intensity is observed for the 300-min milled mixture annealed at 1000℃ for 1 h with a Nd~(3+) concentration of 1 mol%.The PL peaks excited by 800 nm radiation were detected,centered at 1080 nm(~4 F_(3/2)→~4 I_(11/2)) and 1350 nm(~4 F_(3/2)→~4 I_(13/2)).     

Phase constitutions,growth pattern and mechanical properties of Mg-1.4Gd-1.2Y-xZn-0.15Zr(at%) alloys

The effects of minor Zn(0.2 at%,0.4 at%,0.6 at%) on the microstructures and mechanical properties of Mg-1.4 Gd-1.2 Y-0.15 Zr(at%) alloys were systematically explored.Results reveal that increasing Zn content leads to the increase of the intergranular phases and the change of their composition from Mg_24(Gd,Y)_5 phase and(Mg,Zn)_3(Gd,Y) phase to 18 R-LPSO phase and(Mg,Zn)_3(Gd,Y) phase.Mg_24(Gd,Y)_5 phase is body-centered cubic structure and shares the same lattice constant with Mg_24Y_5 while(Mg,Zn)_3(Gd,Y)phase is face-centered cubic structure with lattice constant of 0.72 nm,slightly lower than Mg_3Gd.18RLPSO structure is identified to be monoclinic with c-axis not strictly vertical to the bottom surface but93.5°.The growth patterns of intergranular phases change from the divorced growth to coupled growth as compositions change.Moreover,the mechanical performance improves with Zn rising,ascribed to the decrease of brittle phases at grain boundaries and the increase of LPSO structure phases.     

Tetranuclear yttrium and gadolinium 2-acetylcyclopentanoate clusters: Synthesis and their use as spin-coating precursors for metal oxide film formation for field-effect transistor fabrication

Lanthanide clusters [Ln_4(μ_3-OH)_2(η~2-accp)_4((μ-O)-η~2-accp)_6](Ln = Y(4),Gd(5); accp = 2-acetylcyclopentanoate) are accessible by treatment of [M(NO_3)_3·6 H_2 O](M = Y(1),Gd(2)) with 3 equiv. of Haccp(3) in presence of NaOH. The molecular structures of 4 and 5 in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O_2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O_2. PXRD measurements of the TG residues confirm the formation of Ln_2 O_3.Spin-coating experiments were carried out with 4 and 5 for Ln_2 O_3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87±1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y_2 O_3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y_2 O_3 as a gate dielectric in electronic devices.     

Structural,morphological and optical properties of new Eu-doped and vacancied lead molybdato-tungstates

A new tetragonal,scheelite-type Pb_(1-3 x)■_xEU_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x)(0 x ≤0.1970 and ■ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction(XRD) and scanning electron microscopy(SEM) results confirm the formation of single, tetragonal scheelite-type phases(space group I4_1/a) with the average crystallite size in the range of ～20-100 μm. Substitution of Pb~(2+) with Eu~(3+) is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO_4 framework. A change in lattice parameters(both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO_4 and WO_4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb_(1-3 x)■_xEu_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x) solid solution for x=0.0098 shows the highest melting point(1057 ℃) which is slightly higher than that of pure PbMoO_4(1040 ℃). The UV-vis diffuse reflectance spectroscopy(DRS) and the Tauc plots were used to extrapolate the optical indirect band gap(E_g) of doped materials. Eu-doped ceramics are insulators(E_g 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.     

Effect of rare earth and transition metal La-Mn substitution on electrical properties of co-precipitated M-type Ba-ferrites nanoparticles

In the current research work Ba_(1-x)La)xMn)yFe_(12-y)O_(19) hexa-ferrite nanoparticles of different compositions were synthesized using chemical co-precipitation technique. The structural properties were explored using X-ray diffractions(XRD), scanning electron microscopy(SEM) and Fourier transmission infrared spectroscopy(FTIR). XRD indexed pattern confirms the formation of M-type hexagonal phase. The crystallite size of synthesized samples ranges from 13 to 34 ± 2 nm. FTIR peaks observe also confirmed the presence of metaloxygen bond of the desired product. The position of peak at 467 cm~(-1) corresponds to A_2 u vibration for octahedral Fe(4+)-O and peak position E1 u corresponds to vibration of Fe(3+)O4 octahedral bonds. The band v_1 in range(677-559 cm~(-1)) and v_2 in frequency range(356-419 cm~(-1)) are associated to A and B sites.Dielectric properties of all compositions were measured with frequency. The dielectric constant, loss and tangent loss decrease from 26 to 9, 25 to 2 and 0.94 to 0.14, respectively with frequency. DC electrical resistivity is increased with dopant concentration increasing from 2.15 × 10~4 to 1.92 ×10~5 Ω·cm.     

Synthesis and luminescence of Eu3+ doped nanocrystalline TiO2 spheres

Eu~(3+) doped TiO_2 anatase spheres were obtained by modified sol-gel approach.Spheres(110—250 nm) are composed of smaller(5-15 nm) nanocrystals and exhibit red emission under UV light excitation.Materials were synthesized by multi-step method from glycolated titania alkoxides.Europium doped(1.0 mol%) and non-doped spheres were synthesized.Their optical and structural properties were compared by materials characterization methods,such as X-ray powder diffraction,transmission electron microscopy and PL spectroscopy.Doped TiO_2 spheres are crystalline phase pure and exhibit high luminescence intensity.     

Synthesis and luminescent properties of BaGd2O4:Eu3+ phosphors with highly efficient red-emitting

The BaGd_(2-2 x)Eu_(2 x)O_4(BG, x = 0.01-0.09) phosphors were successfully synthesized via the sol-gel method,and BaY_(2-2 y)Eu_(2 y)O_4(BY, y = 0.005-0.07) phosphors were included for comparison. The pure phase BG phosphors with the ordered CaFe_2 O_4-type structure are obtained by annealing at 1300℃ for5 h. The phosphors with uniform particle size of 120 nm and good dispersion display typical Eu~(3+)emission with the strongest peak at 613 nm(~5 D_0→~7 F_2 transition of Eu3+) under optimal excitation band at 262 nm(CTB band). The presence of Gd~(3+) excitation bands on the PLE spectra monitoring the Eu3+emission directly proves an evidence of Gd~(3+)-Eu~(3+) energy transfer. Owing to the concentration quenching, the optimum content of Eu3+ addition is 5 at%(x = 0.05), and the quenching mechanism is determined to be the exchange reaction between Eu3+. All the BG samples have similar color coordinates and temperature of(0.64 ± 0.02, 0.36 ± 0.01) and 2000 ± 100 K,respectively. The lifetime value of BaGd_(1.9)Eu_(0.1)O_4 for 613 nm is fitted to be 2.19 ± 0.01 ms, and the Eu~(3+) concentration does not change the lifetime significantly. Owing to the Gd~(3+)-Eu~(3+) energy transfer, the luminescent intensity of the BaGd_(1.9)Eu_(0.1)O_4 phosphor is better than BY system. The BG system served as a new type of phosphor is expected to be widely used in lighting and display areas.     

Synthesis and characterization of yttrium and antimony codoped SnO2 conductive nanoparticles

Y was used as a dopant in preparing conductive powder to improve its performance. Y and Sb co-doped SnO₂ conductive nanoparticles were prepared by the complexation-coprecipitation method with Sn, Sb₂O₃ and Y₂O₃ as the raw materials. Crystal phase, thermal behavior and structure of the prepared conductive nanoparticles were characterized by X-ray diffraction (XRD), thermal analysis (TG-DSC), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM) techniques, respectively. The Y and Sb co-doped SnO₂ conductive nanoparticles with a structure of tetragonal rutile had intense absorption in 4000-2500 cm^?1, and the diameter ranged from 10 to 30 nm. The resistivity of Y and Sb co-doped SnO₂ conductive nanoparticles was as low as 0.09 Ω·cm which was 4.6 times lower than that of Sb doped SnO₂ conductive nanoparticles.     

Improved luminescence and photocatalytic properties of Sm3+-doped ZnO nanoparticles via modified sol-gel route:A unified experimental and DFT+U approach

In the current study,a modified sol-gel route was used to produce undoped and Sm³⁺ doped(1 mol%,3 mol% and 5 mol%) ZnO nanoparticles(NPs).The study of opto-structural properties of Sm³⁺ doped NPs was carried out both experimentally and theoretically.Complete dissolution of Sm³⁺ ions into the ZnO lattice is obviously seen from X-ray diffraction(XRD) analysis.Morphological evolution with doping was studied using field emission scanning electron microscopy(FESEM) an...     

Luminescence properties of dysprosium doped YVO4 phosphor

Trivalent dysprosium(Dy~(3+)) activated nanocrystalline yttrium vanadate(YVO_4) phosphor was synthesized via co-precipitation method. The prepared samples were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), optical absorption and photo luminescence(PL) techniques. The XRD patterns reveal the tetragonal crystalline phase. SEM images reveal that Dy doped YVO_4 nanocrystals are agglomerated. EDAX confirms the formation of YVO_4:Dy. FTIR spectrum shows two strong absorption bands at 459 and 761 cm~(-1). Optical absorption spectrum showed the surface defects in the as-prepared samples. The PL emission spectrum shows two characteristic emission bands at 485 and 575 nm. The strong yellow emission peak at 575 nm is assigned to ~4 F_(9/2)→~6 H_(13/2) hyper sensitive transition of Dy~(3+) ions, Study of CIE chromaticity diagram indicates the suitability of the phosphor for the development of yellow-green LEDs.     

Hydrothermal synthesis,structure study and luminescent properties of YbPO4:Tb3+ nanoparticles

YbPO₄:Tb³⁺ were synthesized by mild hydrothermal method. The luminescent properties, morphologies and structure of the obtained powders were characterized by photoluminescence (PL) spectra, FESEM, X-ray diffractometer (XRD) and FTIR. The results showed that the prepared YbPO₄:Tb³⁺ nanoparticles were pure tetragonal phase and the average grain size varied with increasing of Tb³⁺ concentration. Hydrothermal temperature was revealed to be the key factor to enhance the emission intensity of YbPO₄:Tb³⁺ phosphors. The spherical nanoparticles could be effectively excited by near UV (369 nm) light and exhibited green performance at 543 nm (⁵D₄→⁷F₅), 489 nm (⁵D₄→⁷F₆) and 586 nm (⁵D₄→⁷F₄). The CIE chromaticity was calculated to be x=0.298, y=0.560. The YbPO₄:Tb³⁺ nanoparticles exhibited potential to act as UV absorber for solar cells to enhance the conversion efficiency.     

Synthesis,structure and luminescent properties of a new Vernier phase Lu7O6F9 doped by Eu^3＋ as potential scintillator with unique lath tube architecture

To explore novel nano-scintillator with a controllable architecture, pure and Eu3+ doped lutetium oxyfluoride(Lu7O6F9) powder were synthesized by combining mild hydrothermal method and solid state calcination approach. The products were all pure orthorhombic Vernier phase demonstrated by X-ray powder diffraction(XRD). The detailed crystal structure was also studied by Reitveld refinement. Lath-like microcrystals composed of nanoparticles with unique hollow tube of the products were supported by the images of scanning electron microscopy(SEM) and transmission electron microscopy(TEM). Excited by X-ray with W as the target, the pure product showed intense broad emission with the peak at about 400 nm suitable for modern photoelectric multiplier tube(PMT), while the Eu3+ doped sample transferred the incident energy to Eu3+ ions and gave strong 5D0→7Fj(j=0, 1, 2 and 4) emission, which fitted for imaging and labeling measurements. From the luminescent properties, both pure and Eu3+-doped products are potential excellent scintillator for X-ray imaging and other high energy detectors, and the pure product is also a good host candidate for rare earth doping.     

Influence of dysprosium concentration on sensitivity of luminescent thermometers of phosphors Ca_9Tb(PO_4)_5(SiO_4)F_2

Tb~(3+),Dy~(3+)-co-doped Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)F_2 phosphors were prepared via high-temperature solidphase reaction method and the potential application in optical temperature measurements due to their color-tunable property was investigated in detail.The photoluminescence emission(PL) and photoluminescence excitation(PLE) spectra results show that the as-prepared phosphors exhibit both Tb~(3+) and Dy~(3+) emissions at 546 nm(~5 D_4-~7 F_5 transition of Tb~(3+)) and 587 nm(~4 F_(9/2)-~6 H_(13/2) transition of Dy~(3+)) upon376 nm excitation,respectively.In addition,the fluorescence decay analysis shows that the lifetime of the Tb3+emission rapidly decreases,which confirms the energy transfer existence between Dy~(3+) and Tb~(3+).Under 376 nm excitation,the temperature dependence of the fluorescence intensity ratios for the dualmission bands peaked at 546 and 587 nm was studied in the temperature range from 303 to 573 K.The results show that with the increase of Dy~(3+) concentration,the relative sensitivity first increases and then decreases,what's more,the maximum relative sensitivity is 3.142×10~(-3)%/K for Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)-F_2(x=0.4).As a consequence,this preliminary study provides a novel method for exploring the novel thermo meters.     

Characterization and electrochemical performance of CeO2 and Eu-doped CeO2 films as a manganese redox flow battery component

Hexagonal CeO_2 and Eu-doped CeO_2 nanoparticles were obtained using a facile microwave-hydro thermal method under mild conditions and their application towards manganese redox flow battery component were studied. The structural properties were studied by X-ray diffraction and indicate that samples present a fluorite structure. Raman spectroscopy shows Eu3+ ions substitute Ce~(4+) and generate oxygen vacancies. Electrochemical properties of pure and Eu-doped CeO_2 films deposited at graphite substrates investigated by cyclic voltammetry and galvanostatic charge—discharge indicate that dopant concentration affects the electrochemical properties of CeO_2. The increase in the reversibility redox of electrochemical systems observed is attributed to coexistence of Ce~(4+)/Ce~(3+) redox couple confirmed by XPS.Charge—discharge tests display coulombic and voltage efficiency values of above 80% and 90%, respectively. The obtained specific capacity for Ce_(0.99)Eu_(0.01)O_2(372.49 mAh/g) and pure oxide(334.84 mAh/g)indicates that both samples are promising for application in Mn-batteries.