Morphology and luminescence properties of BaMgAl10O17:Eu2+ blue phosphors by Aerosol Flame Deposition

BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) is widely used as a blue phosphor for fluorescent lamps and plasma display panels (PDP). The improvement of the luminescence efficiency is a significant issue for applications in plasma display panels. In this study, the Aerosol Flame Deposition (AFD) was applied to fabricate BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) particles with spherical shape and fine size in order to improve their luminescence. The sub-micrometer powder was synthesized in spherical shape in an oxy-hydrogen flame and deposited on a substrate in the form of porous film. The particle size of as-prepared powder increased with increasing the concentration of precursor solution and the heat treatment under reducing atmosphere increased particle size additionally with surface roughening due to the needle-like crystallized phases. Photoluminescence spectrum was observed at about 450nm due to the 5d–4f transition of Eu²⁺ and the intensity of phosphor was as high as 70% of that of the commercial phosphor.     

Microstructure and luminescent properties of Eu2W2O9 phosphors

A homogeneous Eu₂W₂O₉ phase with small grains (～4.0μm) was formed for the specimens fired below 1175°C. As the firing temperature was increased above 1150°C, grain growth occurred and the grain shape changed from faceted to round. The excitation spectra of the Eu₂W₂O₉ phosphor were similar to those of the Eu₂(WO₄)₃ phosphor, but the absorption band due to the O^2?→W⁶⁺ ligand to metal charge transfer was shifted to lower energies and the ⁷F_o→⁵H₃ and ⁷F_o→⁵F_2,4 transitions were not found. The intensity of the excitation and emission spectra of the Eu₂W₂O₉ phosphor considerably increased with increasing firing temperature, due to the increased grain size and changed grain shape. The intensity of the red emission band of the Eu₂W₂O₉ phosphor was higher than that of the Eu₂(WO₄)₃ phosphor. Moreover, the addition of LiCl to the Eu₂W₂O₉ phosphors considerably enhanced the intensity of their emission spectra, probably due to the increased grain size. Therefore, LiCl-added, Eu₂W₂O₉ phosphor is a promising candidate material for red color emission.     

Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors

Photoluminescence and photocurrent characteristics of Eu^{2 +} activated MAl₂O₄ (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy^{3 +} as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested. The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl₂O₄ with only Eu^{2 +} as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl₂O₄ showed a good proportional relationship to UV and visible light intensity. Especially, SrAl₂O₄ showed an excellent linearity within 1–5 mW/cm², but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

Epitaxial recrystallization and luminescence of CaAl2O4:Eu2+ thin films prepared on sapphire substrates

Eu²⁺ doped CaAl₂O₄ thin films were prepared on c-, a-, and r-plane sapphire substrates by a sputtering method, and then post-annealed for the recrystallization. Post-annealed films have out-of-plane epitaxial orientations of (010) and (001) CaAl₂O₄ on c- and a-plane sapphire substrates, respectively, whereas the films on r-plane were composed of two epitaxial phases of (210) CaAl₂O₄ and (210) CaAl₄O₇. In-plane relationships between films and substrates were also determined by an X-ray pole figure method, demonstrating that the films were epitaxially recrystallized, but not single crystals. The emission wavelengths were independent of the orientations of epitaxial films, showing a blue emission at 448 nm under 325 nm excitation, but the emission intensity depended on the film structure.     

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.     

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.     

液相法制备的LiV3O8的电化学性能

采用液相法合成了LiV3O8电极材料.X射线衍射分析表明:产物(100)衍射峰强度与用高温固相方法得到的相比明显降低.将其作为水溶液电解质锂离子电池的负极材料,恒流充放电结果显示:在-1.5～-0.2 V(vs.SCE)电位范围内,产物的首次放电比容量可达96 mAh/g.研究了导电剂乙炔黑的添加量对电极的首次放电比容量的影响,发现乙炔黑的添加量在10%左右最佳.     

沉淀法Al_2O_3对填充锂正极材料性能的影响

解决单质硫导电性问题是提高锂硫电池性能的关键。纳米氧化物不仅能提高硫电极的孔隙度,还能吸附较多硫离子,对电池的氧化还原反应起到催化作用。研究了纳米氧化物Al_2O_3对单质硫电化学性能的影响,并采用X射线衍射光谱法(XRD)、扫描电子显微镜法(SEM)、粒度分析仪对电池材料物相、颗粒形貌和粒度分布进行表征。利用高精度电池性能分析测试系统对正极材料、电池进行电性分析。     

Chemical processing and properties of Sr2(Ta,Nb)2O7 thin films

Abstract

The crystallographic orientation, microstructure and electrical properties of Sr₂(Ta, Nb)₂O₇ thin films strongly depended on the composition (Ta:Nb). Post-annealing at 850°C was effective for the improvement of some properties. The thin films with relatively Nb-rich compositions, such as Sr₂(Ta_0.6Nb_0.4)₂O₇ and Sr₂(Ta_0.5Nb_0.5)₂O₇, showed the (0k0) preferred orientation. The Sr₂(Ta_0.5Nb_0.5)₂O₇ thin film had a lamination layer structure after the post-annealing at 850°C for 6 min in oxygen. The characteristic microstructure originated in the crystallographic orientation of (0k0), which is the cleavage plane, and influenced electrical properties. The dielectric constant little change with the composition, however, the P-E hysteresis properties improved with the Nb content.     

Defects in BaMgAl10O17: Eu2+ Blue Phosphor

The luminescent properties of BaMgAl₁₀O₁₇: Eu²⁺ blue phosphor are closely related to the valence state of europium inside the crystal and its defect structure. Because of the complexity of the BAM structure, research was carried out to study the europium-related defects by computer simulation. Two different Mg distributions were found to have the same lattice energy, but the arrangement of Mg affected the defect energy and Eu position. Eu³⁺ behavior was also discussed to address the oxidation-induced luminescent degradation. Two energetically most-favorable positions were found for europium, depending on the oxidation state: the Beevers-Ross site on the conduction plane for Eu²⁺, and the Al(2) site in the middle of the spinel block for Eu³⁺. Results of defect complex and bond-valence calculations suggested that the large europium ion can reside in the oxygen close-packed spinel blocks. A comparison of europium defect properties calculated with two different potential models suggests that results of the simulations are potential independent.     

尖晶石型LiMn2O4的电化学性质

利用循环伏安法(CV)、恒流充放电、电化学阻抗谱(EIS)等电化学手段研究了溶胶凝胶法制备的尖晶石型LiMn2O4的电化学性质.结果表明用溶胶凝胶法制备的样品放电容量大,可逆性好,其中550℃煅烧的样品电化学性能最好;XRD结果表明,样品经过充放电,尖晶石结构仍保留,但出现深度放电产物Li2Mn2O4.     

水热法制备V_2O_5纳米材料的研究进展

介绍通过简单易操作的水热法制备各种纳米尺寸结构的五氧化二钒(V_2O_5)材料,包括低维度纳米结构材料、二维结构材料和三维结构材料。指出V_2O_5作为正极材料亟待解决的问题(如结构稳定性、电子导电率、锂离子扩散系数等),并展望水热法制备V_2O_5纳米结构材料的发展趋势。     

Synthesis and Luminescence Properties of Eu3+ Doped Sr2SiO4 Phosphor

Abstract

The europium doped Sr₂SiO₄ phosphors were prepared by the combustion synthesis technique. The prepared samples of europium doped Sr₂SiO₄ phosphors were characterized by the X-Ray Diffraction (XRD), Ultraviolet Visible spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectra (EDS) and Photoluminescence Technique (PL). The orthorhombic crystal structure of the prepared sample was confirmed by using XRD. The formation of fiber like nano structured nature was confirmed by the images captured using the FE-SEM technique. The band gap energies were calculated using the UV-Visible spectra of the samples and these band gap energies were observed as 4.5826?eV for Sr₂SiO₄ and 4.1748?eV for Eu (5?m%) doped Sr₂SiO₄. The two different PL emission peaks were observed for two different excitation wavelengths. One peak was observed at the 590?nm under 393?nm excitation and another peak was observed at the 615?nm under 408?nm excitation. The CIE color coordinates of the Eu³⁺ doped Sr₂SiO₄ phosphors are x?≈?0.6615, y?≈?0.3382 (red color) observed for 408?nm excitation and x?≈?0.5636, y?≈?0.4356 (orange) observed for 393?nm excitation calculated using the color calculator program radiant imaging.     

Effect of synthetic conditions on particle size and photo-luminescence properties of Y2O3:Eu3+ nanophosphor

In this paper, effect of synthetic conditions on the particle size, crystal structure, and the photoluminescence properties of the Y₂O₃:Eu³⁺ nanophosphor was investigated. Solvent and dispersing agent were determined as the synthetic parameters. The nanophosphor synthesized from methanol solvent showed the smaller particle size of 4 nm. The XRD analysis indicates that the crystal structure of the Y₂O₃:Eu³⁺ nanophosphor is mainly cubic crystal with orientation of (222), (440), (400), and small peak of (511) indicating monoclinic crystal. The Y₂O₃:Eu³⁺ nanophosphor synthesized by using methanol solvent and 0.1 wt.% hydroxypropyl cellulose (HPC) as a dispersing agent showed higher degree of crystallization of 10.5 of I ₍₂₂₂₎/I ₍₅₁₁₎ ratio than that without HPC. Also, the photoluminescence properties of the nanophosphor showed red color that excitation and emission wavelengths of the nanophosphor were 250 and 611 nm, respectively. Using the 250 nm UV source, the highly intensive photoluminescence peak could be achieved at 611 nm under the synthetic condition of methanol solvent adding 0.1 wt.% HPC.     

Preparation of sputtered SrAl2O4:Eu films and their thermoluminescence properties

SrAl₂O₄ activated with Eu, a new fluorescent material having a long decay time, was deposited on Si substrates using an RF sputtering technique with facing targets. The as‐deposited films did not show any peaks in the X‐ray diffraction spectra and no photoluminescence was observed. However, X‐ray diffraction peaks and a photoluminescent peak at about 520 nm were observed after annealing in a reducing Ar+H₂ gas and an inert Ar gas. The structure of the sputtered films was investigated using EDS and SEM. The thermoluminescence peaks were observed, and the lifetime of the fluorescence and the activation energies were calculated from the peaks. The results in this work are useful for future applications. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 7–14, 2000     

Electrical properties of TiO2 thin films prepared by the sol-gel method

A TiO₂ thin film was prepared by the sol-gel method using a metal alkoxide [Ti(O-i-Pr)₄ tetrasopropoxy titanium: TIPT]. The crystalline form of the film depends on the preparation conditions and the heat treatment temperature. When the ratio (γ) of H₂O to TIPT is 7, the crystalline phase is formed at 400°C; when γ = 2 it is formed at 500°C. The anatase crystal structure was obtained for both γ = 2 and γ = 7. The electrical conductivity of the TiO₂ film increased with the heat treatment temperature.     

Epitaxial Growth and Luminescent Properties of Mn2+-Activated ZnGa2O4 Films

The epitaxial growth and properties of Mn²⁺-doped ZnGa₂O₄ thin films on various single crystal substrates using pulsed laser deposition were investigated. Control of Zn/Ga stoichiometry required the use of a mosaic ZnGa₂O₄/ZnO ablation target to compensate for Zn loss due to evaporation. The photoluminescent intensity was a strong function of the Zn/Ga ratio, and also correlated with changes in the surface morphology. Superior photoluminescent intensity was attained from slightly Zn-deficient films which exhibit distinctive worm-like surface features. Enhanced photoluminescent intensity was observed in epitaxial films as compared to randomly-oriented polycrystalline deposits on glass substrates, suggesting an adverse effect of grain boundaries on luminescence properties.     

LiMn2O4的甘氨酸法合成

用甘氨酸法合成锂锰氧化合物,通过FTIR、NMR和TG/DTA等研究了锂锰.甘氨酸前驱体的组成、结构和锂锰氧化舍物的形成机理,并对LiMn2O4样品进行XRD分析.甘氨酸法可在低温下反应,得到原子级水平混合的锂离子与锰离子前驱体;在356℃左右就可得到尖晶石LiMn2O4;在400℃下煅烧合成的样品以纯尖晶石LiMn2O4存在,在750℃下煅烧合成的LiMn2O4样品,0.2 C首次放电比容量为119.8 mAh/g,20次循环后放电比容量为118.4 mAh/g.     

Photoluminescence properties of a green to red-emitting Eu3+, Tb3+ co-doped CaBi2Ta2O9 ferroelectrics

The CaBi₂Ta₂O₉ bismuth layered-structure ferroelectrics doped with rare earth ions Eu³⁺ and Tb³⁺, or co-doped with Eu³⁺/Tb³⁺ were prepared by the conventional solid-state reaction method. The microstructure and photoluminescence properties of CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ were investigated. The XRD patterns demonstrate that the rare earth ions have been effectively doped into CaBi₂Ta₂O₉ host lattices. The photoluminescence properties of CaBi₂Ta₂O₉ with different activator ions are researched in details. The novel red and green light emissions were observed under the excitation of blue and near-UV light. Notably, tunable emissions and a warm-white color have been achieved in the Eu³⁺ and Tb³⁺ co-doped CaBi₂Ta₂O₉ powders. These results suggest that CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ could be novel luminescence materials. It is also expected that rare earth doped CaBi₂Ta₂O₉ ferroelectrics can find potential applications in new multifunctional photoluminescence ferroelectric devices.