Characteristics of ZnGa2O4 phosphors synthesized by solution combustion method

ZnGa₂O₄ phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn⁺² ions. The highest PL peak was observed with Mn⁺² ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.     

Luminescent properties of Sr2ZnSi2O7: Eu2+ phosphors prepared by combustion-assisted synthesis method

A blue-emitting phosphor Sr₂ZnSi₂O₇: Eu²⁺ was prepared by combustion-assisted synthesis method and an efficient blue emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 475?nm, which corresponds to the 4f⁶5d¹??4f⁷ transitions of Eu²⁺. The excitation spectrum is a broad band extending from 250 to 450?nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The effect of doped Eu²⁺ concentration on the emission intensity of Sr₂ZnSi₂O₇: Eu²⁺ was also investigated and the corresponding concentration quenching mechanism is verified to be an electric multipole-multipole interaction.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Ferroelectric Properties of the La0.03Sr0.225Ba0.7Nb2–yTiyO6–y/2 Ceramic System

The study of the dielectric properties of the stoichiometric Titanium doped Sr_0.255La_0.03Ba_0.7Nb₂O₆ ceramics prepared according to the formula Sr_0.225La_0.03Ba_0.7Nb_2–yTi_yO_6–y/2 is reported. A single phase compound is observed for low Ti content (y<0.1) in the XRD spectra, being isostructural with the SBN phase. For high Ti concentrations (y<0.1), the XRD patterns show, besides the SBN phase reflections, several small peaks associated with an additional phase present in the ceramics. A possible liquid phase sintering is analyzed. Strongly broadened dielectric curves are obtained in dielectric measurements, where the transition temperature decreases with the Titanium content. The diffuse phase transition coefficients are calculated, corroborating that Titanium increases the diffuse character of the transition in the monophasic region.     

Deposition of Europium Oxide on Si and its optical properties depending on thermal annealing conditions

We investigate the influence of the ambient gas during thermal annealing on the photoluminescence (PL) properties of europium compound thin films on Si substrates. The films were deposited by radio-frequency magnetron sputtering and subsequently annealed in N₂ or O₂ ambient gas by rapid thermal annealing (RTA). The results of X-ray diffraction indicate that the resulting europium compound annealed in N₂ ambient have several silicate phases such as EuSiO₃ and Eu₂SiO₄ compared to those annealed in O₂ ambient. The spectral results revealed that a broad luminescence associated with Eu²⁺ ions, with a maximum intensity at 600 nm and a FWHM of 110 nm, was observed from the thin film annealed at 1000 °C in N₂ ambient. However, a series of narrow PL spectra from Eu³⁺ ions were observed from the film annealed in O₂ ambient.     

Synthesis and temperature-dependent optical properties of Eu3+-doped NaYSiO4 red-emitting phosphors

Abstract

Novel Eu³⁺-activated orthosilicate NaYSiO₄:xEu³⁺ (x?=?0.02, 0.05, and 0.20) red-emitting phosphors were developed for white light emitting diode applications. The X-ray diffraction (XRD), photoluminescence excitation and emission spectra, temperature-dependent curves were applied to characterize the samples. The red emission of the NaYSiO₄:Eu³⁺ phosphor corresponding to ⁵D₀→⁷F₂ (614?nm) transition was observed under the excitation of 394?nm wavelength, which is suitable for UV LED chip. The quenching temperature for NaYSiO₄:0.05Eu³⁺ was found to be over 500 K. The CIE chromaticity coordinates of NaYSiO₄:0.05Eu³⁺ are very close to the National Television System Committee (NTSC) standard red.     

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y₂O₃: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y₂O₃: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu^{3 +} and Bi^{3 +} concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.     

Low dielectric dissipation and enhanced tunability of Ba0.6Sr0.4TiO3 thin films by the modified composition and multilayer structure

Ba_0.6Sr_0.4Ti_1+yO₃ (BST, y?=?0.1, 0.15, 0.2, 0.25, 0.3) thin films were fabricated on Pt-coated silicon substrates by modified sol-gel techniques. It was found that the tunability of BST thin films and dissipation factor decreased with the increase of Ti content. The multilayer structure of Ba_0.6Sr_0.4Ti_1+yO₃(200 nm)/Ba_0.6Sr_0.4TiO₃(100 nm)/Ba_0.6Sr_0.4Ti_1+yO₃ (200 nm; y?=?0.1, 0.2, 0.25) was designed to enhance the tunability. Our results indicated that the modified composition and multilayer structure were beneficial to lowering the dielectric dissipation and enhancing the tunability simultaneously. The tunability of 26.7% and dielectric dissipation of 0.013 were achieved for modified BST thin films.     

Characterization of Ni/Ce Co-Doped BST Thin Film Grown on LSCO/Pt Electrodes Prepared by Pulsed Laser Deposition

Perovskite (Ba_0.6Sr_0.4)TiO₃ (BST) thin films doped with Ni, Ce and Ni/Ce codopants were prepared on LSCO/Pt/SiO₂/Si substrates by pulsed laser deposition method. In this study, La_0.5Sr_0.5CoO₃ (LSCO) bottom electrodes were used to improve the crystallinity and dielectric properties of BST films. Single ion doped(1 mol%Ni doped,1 mol%Ce doped) BST films showed more improved crystallinity, smoother surface, and smaller grain size than that with 1 mol%Ni/1 mol%Ce. The dielectric constant and loss of Ni/Ce co-doped BST films were about 298 and 1.8%, respectively. In addition, tunability and figure of merit of co-doped BST films showed minimum values of approximately 9.3% and 5, respectively. With 1% Ni-doped BST thin films, results gave a tunability of 54.2% and a loss tangent of 1.8% while a figure of merit was 30. Correlation of the material properties with dielectric and tunable properties suggests the 1 mol%Ni-doped BST films are effective potential candidate for tunable device applications.     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

An Abnormal Photoluminescence Enhancement in (Eu,Yb) Co-doped SiO2 Thin Film

We report on the photoluminescence (PL) properties of europium (Eu) and ytterbium (Yb) co-doped SiO₂ thin film. The Eu (both Eu²⁺ and Eu³⁺) PL and the Yb³⁺ PL is co-related under different temperature annealing. However, upon 1100°C anneal, the Eu PL intensity is significantly stronger than other temperatures anneal. Transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction results, suggest that meta-stable Eu²⁺-related silicates (EuSiO₃) have formed in the oxide as well as the formation of Yb₂Si₂O₇.     

Cathodic Polarization Study on Doped Lanthanum Gallate Electrolyte Using Impedance Spectroscopy

The perovskite electrolyte La_{1 – x}Sr_xGa_{1 – y}Mg_yO₃ (LSGM) has received a lot of interest in recent years after it was first reported to have significantly higher oxygen-ion conductivity than conventional YSZ. A very large fraction of the total polarization losses in SOFC is known to occur at the electrode-electrolyte interfaces manifesting itself as the kinetic barrier to charge-transfer reactions. AC complex impedance spectroscopy studies were conducted on symmetrical cells of the type [air, electrode/LSGM electrolyte/electrode, air] to measure the charge-transfer polarization at the cathode-electrolyte interfaces. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The cathode materials investigated in this study include La_{1 – x}Sr_xMnO₃(LSM), LSCF (La_{1 – x}Sr_xCo_yFe_{1 – y}O₃) and a two-phase particulate composite consisting of LSM +doped-lanthanum gallate (LSGM). Symmetrical cell studies were also performed on SOFC anode materials. The principal anode material investigated in this study is a porous composite of Ni-gadolinium doped ceria (GDC). It is well known that Ni reacts with the state-of-the-art LSGM anode material. Thus our approach is to use a barrier layer of GDC between the Ni-GDC anode and the LSGM electrolyte. This paper will focus on the influence of microstructure, electrode composition, electrode thickness, interfacial compatibility and electrode processing conditions on cathode and anode polarization.     

Electrical and memory window properties of Sr0.8-xBaxBi2.2Ta2-yZryO9 ferroelectric gate in metal-ferroelectric-insulator-semiconductor structure

Electrical characteristics of Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ ferroelectric films grown on HfO₂/Si wafers by sol–gel spin coating technique were investigated from the viewpoint of application as ferroelectric gates in metal-ferroelectric-insulator-semiconductor (MFIS) stacks. It was observed that the leakage current density level was 10^-8 A/cm² under 14?V for moderate doping ratio. Determined memory windows from C-V characteristics of Sr_0.8Bi_2.2Ta₂O₉ (SBT) and Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ (x?=?0.04, 0.08, 0.12 and y?=?0.1, 0.2, 0.3) are 0.59, 0.65, 0.75, and 0.86?V at gate sweeping bias of 5?V, respectively. Some part of electronic properties of Sr_0.8-xBa_xBi_2.2Ta_2-yZr_yO₉ with the objective to enhance memory window up to 45?% were discussed. It was interpreted that defects which are formed in Ba and Zr modified SBT affected the electronic processes like leakage current, memory window and charge trapping.     

Electrical Properties of the Titanium Modified SBN Ceramic System

The electrical properties of the Sr_0.3Ba_0.7Nb₂O₆ system modified with different concentrations of titanium, following the general formula Sr_0.3Ba_0.7Nb_2–y Ti _y O_6–y/2 for charge compensation, are studied. The investigation is carried out in samples prepared by the conventional ceramic method. The X-ray diffraction analysis shows tetragonal tungsten bronze monophasic compounds in all cases. Dielectric measurements show a typical ferroelectric behavior with diffuse phase transition, where the transition temperature and the maximum permittivity decrease with increasing titanium content. The remanent polarization is obtained from hysteresis measurements in the ferroelectric region, while at high temperatures, two processes (a conductive and a ferroelectric process) are overlapping. The diffuse character of the ferroelectric-paraelectric phase transition is also studied and the diffusivity coefficient calculated in all cases.     

The effect of heat treatment temperature on phase formation and luminescence properties of calcium magnesium silicate glass-ceramics doped with Sm2O3

Abstract

The transparent glasses of CaO-MgO-Al₂O₃-SiO₂-ZnO system doped with Sm₂O₃ was prepared by conventional melt-quenching method. The obtained glasses were heat treated at a suitable temperature (875?°C–920?°C for 2?h) identified by differential thermal analysis (DTA). Phase formation and microstructure of glass-ceramics were characterized by X-ray diffraction and scanning electron microscopy, respectively. The optical transmission spectra were recorded by UV-Vis spectrophotometer in the wavelength range between 350 and 1000?nm. It was found that the increase in heat treatment temperature reduced the transparency of the glass-ceramics. The luminescence properties were identified by fluorescence spectroscopy. The excitation spectra of Sm₂O₃ doped CaO-MgO-Al₂O₃-SiO₂-ZnO glass-ceramic samples are in wavelength range of 550–750?nm and the emission spectra exhibited a strong orange-red luminescence composed of 562, 599 and 654?nm under excited at 402?nm. The results of XRD studies revealed the occurrence of diopside (CaMgSi₂O₆) and akermanite (Ca₂MgSi₂O₇) phases. The increasing of heat treatment temperature has no effect on the shift of emission spectra.     

白光LED用Li2+y(Gd1-xEux)4（MoO4）7-y（BO3）y新型红色荧光体

首次报道了采用高温固相反应合成Li2+y(Gd1-xEux)4(MoO4)7-y(BO3)y(0相似文献   

ZnGa2O4 thin films fabricated by Sol-gel spinning coating process

ZnGa₂O₄ thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500^∘C and an annealing temperature of 500^∘C and 600^∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution. XRD patterns of the film phosphors synthesized showed the peaks of ZnGa₂O₄ crystalline phases. AFM surface morphologies of the ZnGa₂O₄ thin film phosphors revealed marked differences according to an annealing temperature of 500^∘C and 600^∘C under an annealing atmosphere (3% H₂/Ar). On the other hand, the sheet resistance of ZnGa₂O₄ thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square with annealing temperature, respectively. The ZnGa₂O₄ thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation around 230 nm.     

Characterization of Pr- and Sm-Doped Ce0.8Gd0.2O2 − δ

Ce_0.8Gd_{0.2 – y}Pr_yO_{2 –} (y = 0–0.05) and Ce_0.8Gd_{0.2 – y}Sm_yO_{2 –} (y = 0–0.05) SOFC electrolyte materials were prepared using a reverse-strike co-precipitation method. The resulting powders were characterized using X-ray diffraction, Raman spectroscopy and electrochemical methods. XRD confirmed a single fluorite phase for all compositions. Increased Pr and Sm dopant level was found to cause a shift in the peak positions to slightly higher d-spacings with respect to pure CeO₂. The experimental lattice parameter was calculated using the peak positions determined from the XRD patterns. Raman spectra, for all dopant levels, showed two distinctive band features, namely a band at ca. 460 cm^{– 1} and a broader, weaker band at ca. 570 cm^{– 1}. As the proportion of praseodymia dopant is increased, the oxygen vacancy band shifts to a slightly lower wavenumber and decreases in relative intensity to the F_2g band. However, an anomaly occurs at the 1% dopant level; the oxygen vacancy band having a very low relative intensity. The conductivity was determined using AC—impedance spectroscopy, and it was found that for praseodymia, a maximum is observed at y = 0.015, while for samaria the maximum is observed at y = 0.01. It is also observed that the ionic conductivity for the samaria doped samples are lower than those of the praseodymia doped samples.     

Influence of Y and Mn alternately doped order on the microstructures and dielectric properties of Ba0.6Sr0.4TiO3 films

ABSTRACT

The influences of Y and Mn alternately doped order on the microstructures and dielectric properties of the Ba_0.6Sr_0.4TiO₃ (BST) films were reported in this paper. The Y and Mn alternately doped BST films were designed as YBST/MnBST/… and MnBST/YBST…multilayer films orderly expressed as (Y/Mn)_M and (Mn/Y)_M for short, and prepared on Pt/Ti/SiO₂/Si wafers by an improved sol-gel method, where Y and Mn represent yttrium doped BST layer and manganese doped BST layer, and M is cycle unit, respectively. The microstructures of the alternately doped BST films were observed by SEM and the capacitance-voltage curves at 100 kHz or 1 MHz were measured by a HP4284A LCR meter and the dielectric properties in the range of 1GHz were measured by an E4991A impedance analyzer. Compared to Y or Mn doped multilayer BST film, (Y/Mn)_M and (Mn/Y)_M show higher dielectric tunability and lower dielectric loss with higher dielectric constant. Moreover, (Y/Mn)_M show better dielectric properties than (Mn/Y)_M because (Y/Mn)_M show granular microstructures independent of M, while the (Mn/Y)_M show granular microstructures when M is 2 and add to a surface layer of columnar microstructures on the granular microstructures when M is 4. The related mechanisms were obtained in terms of the XRD phase structures, the cross-sectional SEM microstructures and the AFM morphologies.     

Ferroelectric properties of Ba1−x Sr x TiO3 thin films synthesized by using novel sol–gel technique through carbonates

Ba_1?x Sr _x TiO₃ (BST) thin films were prepared on the substrate of Pt/Ti/SiO₂/Si by using novel sol–gel process through carbonates. The surface morphology and domain contrast of the films were investigated by atomic force microscopy (AFM), and the domain structures of the BST film were observed when AFM were operated in piezoelectric force microscopic (PFM) analysis and in the friction mode (FFM). The ferroelectric properties of the films were also investigated. It is shown that BST films obtained by the new sol–gel process through carbonates exhibit good properties.