Sol-gel processed Ce^3＋, Tb^3＋ codoped white emitting phosphors in Sr2Al2SiO7

Sr2Al2SiO7：Ce^3＋, Tb^3＋ white emitting phosphors were fabricated using the sol-gel method. X-Ray Powder Diffraction （XRD） analysis confirmed the formation of Sr2Al2SiO7：Ce^3＋, Tb^3＋. Scanning Electron Microscopy （SEM） observation indicated that the microstructure of the phosphor consisted of regular fine grains with an average size of about 0.5-1 μm. Luminescence properties were analyzed by measuring the photoluminescence spectra. The Ce^3＋, Tb^3＋-codoped Sr2Al2SiO7 phosphors showed four main emission peaks： one at 414 nm for Ce^3＋ and three at 482, 543, and 588 nm for Tb^3＋. The emission spectra of the samples with different doping concentrations showed that the Tb^3＋ emission was dominant because of the persistent energy transfer from Ce^3＋. The decay characteristic was better than that prepared by the solid-state process in the comparable condition. The codoped phosphor displayed long persistent white phosphorescence.     

Synthesis of CaWO4：Eu3＋ phosphor powders via ethylene glycol route and its optical properties

Eu3+ doped CaWO4 with tetragonal system were prepared at comparatively low temperature (125 ?C) in ethylene glycol medium. The phosphor was further investigated by X-ray diffractometer (XRD), photoluminescence spectrophotometer (PL), Fourier transform infra red (FT-IR) spectroscopy and transmission electron microscopy (TEM). XRD analysis indicated a decrease in the unit cell volume of CaWO4 with increasing Eu3+ ion concentration. It indicated the homogeneous substitution of Ca2+ ions in CaWO4 by the Eu3+ ions. TEM images showed that the particle size ranged from 20 to 200 nm and it could extend the application of the nanoparticles. The photoluminescence study showed that the intensity of electric dipole transition (5D0→7F2) at 614 nm dominated over the magnetic dipole transition (5D0→7F1) at 592 nm. The optimum concentration of Eu3+ for the highest luminescence was found to be 20 at.%. The as prepared samples were found to be dis-persible in water and methanol.     

Energy transfer and frequency upconversion in Er~（3＋）-Yb~（3＋） codoped oxy-fluoro-tungstosilicate glasses

Er3+-Yb3+ codoped oxy-fluoro-tungstosilicate glasses with infrared-to-visible frequency upconversion luminescence were prepared by melting quenching in air.The effects of Er3+ doping on the optical properties of the samples were measured by means of techniques such as optical absorption spectra and photoluminescence spectra.The results showed that intense green and red signals centered at 546 and 665 nm,corresponding to the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ by a multiphoton stepwise phonon-assisted excited-state absorption process,respectively,were simultaneously observed by exciting the samples with a diode laser operating at 980 nm at room temperature.The upconversion process was found very sensitive to Er3+ content at a constant Yb2O3 content of 5 mol.%.With the increase of Er3+ content from 0.5% to 1.5%,the upconversion intensity increased gradually.Further increasing of Er3+ content to 3.0% resulted in a significant fluorescence quenching.Moreover,the possible upconversion mechanisms were discussed based on the energy-matching conditions and the quadratic dependence on excitation power.     

Synthesis of Long Afterglow Photoluminescent Materials Sr2MgSi2O7：Eu^2＋,Dy^3＋ by Sol-Gel Method

Long afterglow photoluminescent materials Sr2MgSi2O7 dopeo With Eu^2 ,Dy^3 were prepared by sol-gel method. The synthesized samples were characterized by X-ray diffraction. The excitation spectrum, emission spectrum and long decay curve were measured and analyzed. XRD pattern indicates that phosphor is with Sr2MgSi2O7 crystal structure. The wide range of excitation wavelength indicates that luminescent material can be excited by light from ultraviolet ray to visible light. The main peak of emission spectrum is located at 466nm. Sample excited by visible light can emit bright blue light, and the afterglow time lasts more than 8h.     

Thermoluminescence characteristics and dosimetric aspects of fluoroperovskites （NaMgF3：Eu2＋,Ce3＋）

The perovskite-like NaMgF3 polycrystalline powder samples, pure and rare earth doped, were synthesized by conventional solid state reaction method. The perovskite material was doped with 0.2 mol.% of EuF3 and CeF3 impurity. Phase purity of synthe-sized compounds was analyzed by powder X-ray diffraction technique. The thermoluminescence response of polycrystalline samples showed a linear response up to 12 Gy and then became sub linear at higher doses. The order of kinetics （b）, activation energy （E） and other trapping parameters were calculated using peak shape method and variable heating rate method. From glow curve analysis the symmetric factor was calculated. The glow curve showed two peaks at 404 and 488 K, and both of them confirmed the thermolumi-nescence in the phosphor, which obeyed second-order kinetics. The experimental resulted showed that this phosphor could have po-tential applications in radiation dosimetry.     

Preparation and Characterization of Red Luminescent Ca0.8 Zn0.2 TiO3 ： Pr3 ＋ , Na^＋ Nanophosphor

Nanophosphor with the nominal composition of Ca0.8 Zn0.2 TiO3 ： Pr3 ＋ , Na^＋ （CZTOPN） was synthesized at relatively low temperature by the sol-gel method. Metal ions were dispersed by citric acid in ethylene glycol solvent and then react with Ti（OC4H9）4 to form sol and gel. The decomposition process of the precursor, and crystallization and particle size of CZTOPN were examined by thermal analysis （TG-DSC）, powder X-ray diffraction （XRD）, and scan election microscopy （SEM）. Results of TG-DSC and XRD reveal that the composition of Ca0.8 Zn0.2 TiO3 ： Pr3 ＋ , Na^＋ changes with the sintering temperature. SEM data indicate that the diameter of particles is under 50 nm even if the sintering temperature increases to 1000 ℃. In contrast to a solid state reaction, the excitation spectra of samples synthesized by the sol-gel method shift blue about 10 nm and the emission intensity at 617 nm increases significantly.     

Preparation of lanthanum sulfide nanoparticles by thermal decomposition of lanthanum complex

γ-La2S3 nanoparticles were successfully prepared by thermal decomposition of lanthanum complex La(Et2S2CN)3·phen at low temperature. The obtained sample was characterized by the X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and element analysis. The decomposition mechanism of lanthanum complex was studied by thermogravimetric analyses (TGA). The results showed that the obtained samples were cubic phase particles with uniform sizes among 10-30 nm and γ-La2S3 was prepared by decomposition...     

Preparation and Long Persistence Red Luminescence of M0.2Ca0.8TiO3 ： Pr^3＋ （M = Mg^2＋ , Sr^2＋ , Ba^2＋ , Zn^2＋）

M0.2Ca0.8TiO3 : Pr^3 (M = Mg^2 , Sr^2 , Ba^2 , Zn^2 ) long persistence red phosphors were prepared by solid state reaction. The influence of the partially replacing Ca^2 in CaTiO3 with Mg^2 , Sr^2 , Ba^2 , Zn^2 on the excitation spectra, the emission spectra and the long persistence properties were studied. The results suggest that certain quantity of Mg^2 , Sr^2 , Ba^2 , Zn^2 which partially replace Ca^2 can enhance the luminescent intensity and prolong the afterglow persistence of the samples. The intensity of Mg0.2Ca0.8TiO3: Pr^3 is above all of the samples. Take Mg0.2Ca0.8TiO3:Pr^3 as the basic sample, the influence of Pr^3 concentrations (C (Pr^3 )) on the long afterglow properties were also studied.The results suggest that when the C (Pr^3 ) is 0.10% (tool fraction) the intensity of the sample is the highest. The excitation spectra of all these samples show broad band spectra ranging from 300 - 500 nm peaking at about 342 nm. The emission spectra also exhibit a broad band peaking at 613 nm (CaTiO3: Pr^3 is 612 nm). XRD research indicates that the crystalline phases change due to the replacement of divalent metal ions. The research on the thermoluminescence spectra of Mg0.2Ca0.8TiO3:Pr^3 indicates that the peak is at 107.35℃ and the depth of the trap energy is about 0.852 eV.     

Synthesis of Mesoporous, Nanocrystalline Lanthanum Phosphate in the Presence of Citric Acid and Stearic Acid

Lanthanum phosphate was prepared in the presence of citric acid and stearic acid under methanolic conditions at pH 4.5 and pH 7, respectively. The samples obtained were intensively characterized using X-ray diffraction, nitrogen adsorption-desorption isotherm study, transmission electron microscopy （TEM）, thermal gravimetric and differential thermal analysis, and Fourier transform infrared （FTIR） analysis . The as-synthesized samples prepared at pH 4.5 showed lamellar mesostruroned form with high crystallinity. Results showed that the pore size and pore volume changed when the materials were prepared under different pH conditions. Morphology of the samples was observed by using TEM, which showed that the samples possessed relatively small particles closely packed together. The as-synthesized samples were investigated using FTIR, and the mesopore formation mechanism was discussed.     

Synthesis and Luminescence Properties of Gd2O3：Eu^3＋ Phosphors

Gd2O3: Eu^3 phosphors were prepared by urea homogeneous precipitation with different surfactant and sol-gel method. XRD patterns show that all the obtained samples are in cubic Gd2O3, and the results of FTIR and fluorescent spectra conformed that OP is a good surfactant for preparing the Gd2O3:Eu^3 phosphors. The SEM photographs show that the particles prepared by urea homogeneous precipitation method are all spherical and well-dispersed, and grain morphology can be controlled by different surfactant. XRD and SEM indicate that the particle sizes prepared by sol-gel method are in the range of 5-30 nm, and the grain sizes increase with increasing of heated temperatures. Luminescence spectra indicat that the main emission peaks of all samples are at 610 nm, the intensities are different from samples prepared with different surfactant and the luminescence intensities increase with increasing of annealed temperatures.     

Preparation of Non-Grinding Long Afterglow SrAl2O4 ：Eu^2＋ , Dy^3＋ Material by Microwave Combustion Method

The non-grinding long afterglow material SrAl2O4：Eu^2＋ , Dy^3＋ was prepared by combustion method in home mierowave oven direetly, after dispersant, frother, eomburent, and mineralizer were added into the reacting system. XRD analysis showed that the powders were nearly pure SrAl2O4 phase with few other phases, and the size of the grain was 41.1 nm. Fluoreseenee speetrum results indieated that there were 2 exeitation peaks loeated at 345 and 400 nm, and the emission peak loeated at 516 nm, afterglow lasted up to 30 min or more. The mierowave eombustion method has advantages of less time, low temperature and no grinding process, and the material made by the method has good luminescent property.     

Preparation and Characterization of La0.8Sr0.2MnO3-δ Cathode for SOFCs Fabricated Using Azeotropic Distillation Method

Strontium doped lanthanum manganite (LSM) powders were synthesized by three different routes: azeotropic distillation, sol-gel and solid state reaction respectively. The LSM samples, made by azeotropic distillation and sol-gel methods were prepared by firing at 1000 ℃ for 6 h, and the LSM sample, made by solid state reaction method was produced by sintering at 1400 ℃ for 18 h. The samples were characterized by XRD, TEC, SEM, EIS and polarization performance analysis. The results show that all the samples made by different methods have pure orthorhombic LSM phase, however exhibit different micro structure and electrochemical characterization, which relates to the different synthesis methods. The solid state reaction method produces the samples with larger particle size compared with azeotropic distillation and sol-gel methods. The powders made by azeotropic distillation method have less agglomerated particles compared with that made by sol-gel method because the precursor in the former is dispersed in n-butanol before sintering. The polarization current density of powder made by azeotropic distillation method was twice of that made by sol-gel method and four times of that made by solid state reaction method. The values of polarization resistance (Rp) are 0.35 Ω·cm2 for the cathode synthesized by azeotropic distillation route, which is much lower than sol-gel (1.5 Ω·cm2) and solid state reaction (2.3 Ω·cm2) at 800 ℃.     

A blue luminescence glass-ceramics of Eu^2＋ ions activated Li2O-BaO-B2O3

New blue luminescence glass-ceramic samples were prepared in air by annealing of the Eu^3＋-doped Li2O-BaO-B2O3 glass. The as-made glass samples only showed the sharp emission peaks assigned to the transitions of 5^D0-7^Fj （J=0, 1, 2, 3, 4） of Eu^3＋ ions. The glass-ceramic samples gave a strong and broad emission band peaking at about 382 nm ascribed to the 5d-4f transition of Eu^2＋ ions. The optical properties such as excitation and emission spectra, and the decay time of the Eu^2＋ ions were investigated in the glasses or the glass-ceramics samples. The X-ray diffraction pattern showed that LiBan9O15 might be demonstrated to be the crystallites in the glass-ceramic, which contributed to the blue luminescence. SEM micrograph was investigated on the glass-ceramic samples obtained by crystallization of the glass matrix resulting in a mixture of poly-crystals.     

Luminescence of Er^3＋ in Oxyfluoride Transparent Glass-Ceramics

Erbium doped silicate, germanate, and tellurium-germanate oxyfluoride glasses were prepared in a bulk form. Through appropriate heat treatment of the as-prepared glasses, transparent glass-ceramics (TGCs) were obtained with the formation of β-PbF2∶Er3 nanocrystals in the glass matrix were confirmed by X-ray diffraction. Well-defined diffraction peaks were observed in the samples after heat-treatment. The average crystal diameter of these precipitated crystals from full-width at half-maximum (FWHM) of the diffraction peak was estimated to be between 8 and 13 nm. Optical absorption, photoluminescence, and upconversion luminescence were measured on as-prepared glass and glass-ceramics. Luminescence spectra in the TGC samples revealed well-resolved, sharp stark-splitting peaks, which indicates that a majority of Er3 ions has been incorporated into the crystalline phase of the nanocrystals. The intensity of the visible and near infrared luminescence mostly increases in TSG compared to that in the as-prepared glass. In 1.53 μm absorption and emission bands, the maximum absorption peak is blue-shifted from 1531 to 1507 nm, whereas the maximum emission peak is red-shifted from 1535 to 1543 nm in TGC, as compared with that in glass. The bandwidth at half-maximum (BWHM) of the emission band is significantly broader in TGC than in glass, which is beneficial to the erbium-doped fiber amplifier (EDFA). Upconversion luminescence was measured using 800 nm near-infrared light excitation. Drastically increased upconversion luminescence was observed from the TGC as compared to that from their corresponding as-prepared glasses. In addition to a strong green emission centered at 545 nm because of 4S3/2→4I15/2 transition and a weaker red emission centered at 662 nm because of 4F9/2→4I15/2 transition, generally seen from the Er3 doped glasses, two violet emissions centered at 410 nm because of 2H9/2→4I15/2 transition and centered at 379 nm because of 4G11/2→4I15/2 transition were also observed from the TGC. The increased luminescence was attributed to the decreased effective phonon energy and the increased energy transfer between the excited ions when Er3 ions were incorporated into the precipitated β-PbF2 nanocrystals. The results indicated two attractive spectroscopic properties of the Er3 doped TGC samples, compared to glass samples, namely a reduced multiphonon decay rate and a reduced inhomogeneous broadening. In addition, these oxyfluoride TGC materials were robust, easy and flexibile to process, and possible to be fabricated in the fiber form for device applications.     

Electrospinning synthesis and luminescent properties of Lu₂O₃:Eu³⁺ nanofibers

One-dimensional Lu2O3:Eu3+ nanofibers were prepared by electrospinning followed by high-temperature calcinations.Thermogravimetric and differential thermal analysis,X-ray powder diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,photoluminescent spectra and decay curves were used to characterize the samples.Results showed that samples began to crystallize at ～500 oC and crystallized completely around 1000 oC.The average diameter of nanofibers(1000 oC annealed) was about 55 nm and the particle size of Lu2O3:Eu3+ increased with increasing annealing temperature.Under ultraviolet excitation,nanofibers exhibited typical red emission of Eu3+ in Lu2O3.The effect of heat-treatment temperature on luminescent properties of nanofibers was also discussed.     

Co-Precipitation Preparation and Luminescent Behavior of （ Y, Gd） BO3 ： Eu Phosphor

(Y,Gd) BO3:Eu phosphors were prepared by co-precipitation precursors, and luminescent properties were investigated. The precursors were synthesized by introducing hydroxyl ion to mixed solution of rare earth hitrates and boric acid, either through adding ammonia( precursor 1 )or through controlled release of hydroxyl ion of urea( precursor 2). The precursors were fired in air at 1000℃ for 2 h. Resulted phosphor synthesized with precursor 1 has non-uniformed particle with mean diameter of about 3μm, while that with precursor 2 exhibits uniformed near spherical-like morphology with mean diameter of about 300 nm. Phosphors with the two methods exhibit same crystal structure as that of commercial one. Emission spectra of the samples indicate that the sample prepared with precursor 2 shows relative higher intensity( exited by 172 nm VUV)than that prepared with the other precursor.     

Synthesis, Electrical and Magnetic Properties of Fe304 Doped by Dy^3＋

The Dy^3＋ -doped Fe3O4 samples were synthesized by sol-gel method, and the effects of dopant on the electrical and magnetic properties were investigated. According to XRD analysis, the high concentration doping of dysprosium ions in Fe3O4 can not be obtained due to the difference of ionic radius, and Fe^3 ＋ ions are replaced by only a small amount of dysprosium ions. The magnetic property was characterized by VSM. The substitution results in the change of saturation magnetization, which may be due to the complex effects of increasing magnetization resulted from Dy^3＋ substitution and decreasing magnetization resulted from the impurity. The electrical property was characterized by four-probe method. With the increasing eoped content, magnetoresistance also increases, then decreases, and increases again. The spin-polarization of doped samples is lower than that of Fe3O4. Lower spin-polarization results in lower tunneling magnetoresistance. Fortunately, barrier was obtained by the second phase at the same time when sample was synthesized. The increase of appropriate barrier height leads to the change of tunneling magnetoresistance.     

Preparation of Ultrafine Perovskite Oxide LaMnO3 ＋λ by Supercritical Fluid Drying

Using La2O3 and Mn(NO3)2 as raw materials, the ultrafine lanthanum-manganese aerogel was prepared by sol-gel and surpercritical fluid drying complex technology. Calcining lanthanum-manganese aerogel at 600 and 800℃. The samples were characterized by FT-IR, XRD, TEM techniques and thermo-gravimetric, differential thermal analysis, and using CH4, CO oxidized reaction to inspect the catalytic activity of LaMnO3 λ. The result shows that (1) The method can get brown-blue, well-dispersed ultrafine powder, the existing form of lanthanum is La (OH)3 crystaline, and the existing form of manganese is amorphous condition.     

Synthesis and luminescence properties of CeF3：Tb3＋ nanodisks via ultrasound assisted ionic liquid method

CeF3 and CeF3：Tb3＋ nanocrystals were successfully synthesized by the ultrasound assisted ionic liquid （IL） method at room temperature. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, selected area electron diffraction （SAED）, high-resolution transmission electron micrographs （HRTEM） and photoluminescence （PL） spectra were employed to characterize the nanocrystals. The results of XRD indicated that the obtained samples crystallized well with a hexagonal phase crystal structure. SEM and TEM images demonstrated that the obtained CeF3：Tb3＋ nanocrystals had a discoid shapein the presence of ultrasound and IL, whereas only granular nanoparticles were obtained by magnetic stirring. The possible formation mechanisms of the crystal growth were proposed. The PL spectra of the CeF3：Tb3＋ nanodisks exhibited a strong green emission when excited at 254 nm. Furthermore, the photoluminescence intensity of CeF3：Tb3＋ of the discoid particles was largely improved com-pared with that of the granular nanoparticles.     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8 ：Eu^2＋, Dy^3＋ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8：Eu^2＋ , Dy^3＋ was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis （XRD）. It is found that the single anorthite phase formed at about 1000 %, which is 300 % lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.