Enhancement of photoluminescence of Ba2SiO4：Eu^2＋ by co-doping of La^3＋ or Y^3＋

Green light-emitting Ba2SiO4:Eu2+ phosphors co-doped with La or Y were synthesized by conventional solid-state reaction technique in reductive atmosphere (a mixture of 5% H2 and 95% N2). The results showed that the co-doping of La and Y could greatly enhance the fluorescence intensity of Ba2SiO4:Eu2+ phosphors. The optimum doping concentration expressed by the x value in (Ba0.985-1.5xREx)2SiO4: 0.03Eu2+ (RE=La or Y) was determined to be of 0.05. The excitation and emission peaks of all as-synthesized phosphors were wide bands. The excitation bands ranged from 250 to 400 nm, which matched well with the wavelength of near ultraviolet white light-emitting diodes (LED) chip and could be used as a potential candidate for the fabrication of white LED. The emission bands from 450 to 550 nm were typical 5d-4f transition emission of Eu2+ and displayed un-symmetry profiles because of the two substitution sites of Ba2+ with Eu2+.     

A comparison research on replacements of Ba2+ by Lu3+ and Ba2+-Si4+ by Lu3+-Al3+ in BaSi2O2N2:Eu phosphors

As a cyan-emitting oxonitridosilicate phosphor,BaSi₂O₂N₂:Eu²⁺can be used as a competent cyan compensator to improve the color rendering index of white light-emitting diodes(WLEDs).However,low luminescence efficiency and poor thermal stability of this type of phosphor seriously suppress its actual application in full-spectrum lighting.The replacements of Ba²⁺by Lu³⁺and Ba²⁺-Si⁴⁺by Lu³⁺-Al³⁺can greatly increase the luminescence intensity and improve the thermal stability at the same time.With Lu³⁺doping,the internal quantum efficiencyηIQE Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺is 24.08%higher than that of Ba_0.97Si₂O₂N₂:0.03 Eu²⁺.After Al³⁺co-doping,theηIQE is further increased by 10.31%compared to Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺.When the temperature rises to 473 K,the luminescence intensity of Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺maintains 62.32%of that at room temperature,which increases by 17.35%in relative to the Ba_0.97Si₂O₂N₂:0.03 Eu²⁺,while the luminescence intensity of Ba_0.925Si_1.97O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺,0.03 Al³⁺keeps 73.87%of the initial value,which increases by18.52%compared to Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺.The mechanisms for luminescence and thermal stability improvement are proposed.The Ba_0.925Si_1.97O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺,0.03 Al³⁺cyan phosphor,Y3 Al5 O12:Ce3+yellow phosphor and CaAlSiN3:Eu²⁺red phosphor are mixed thoroughly and coated on a blue LED(450 nm)to assemble a WLED.The WLED demonstrates a color rendering index(Ra)of 97.1 at150 mA,and the R1-R15 values are all above 90.The results indicate that as an effective cyan compensator in WLED,the BaSi₂O₂N₂:Eu²⁺,Lu³⁺,Al³⁺phosphor has great application prospect in the field of full-spectrum lighting.     

Improving luminescence and thermometric performance of Ba2CaWO6:Er3+ by tri-doping with Yb3+ and Na+

The Er³⁺doped double perovskite Ba₂ CaWO₆ crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio(FIR) of transitions from ² H_11/2 and ⁴ S_3/2to the lowered ⁴ I_15/2 level.However,the Ca²⁺vacancy defect caused by the charge difference between rare-earth ions and the substituted alkaline-earth ions gives rise to the non-radiative probability and limits the t...     

聚乙烯亚胺氨基化改性聚偏氟乙烯接枝丙烯酸纤维膜对活性艳红X-3B的吸附研究

以丙烯酸(AA)为接枝单体,通过溶液聚合法在聚偏氟乙烯(PVDF)上接枝AA,制备出PVDF-g-PAA共聚物,再使用聚乙烯亚胺(PEI)对PVDF-g-PAA进行氨基化改性,制备出PEI氨基化PVDF-g-PAA共聚物(PEI-PVDF-g-PAA),再通过静电纺丝法制备出PEIPVDF-g-PAA纤维膜。使用扫描电子显微镜对PEI-PVDF-g-PAA纤维膜的微观结构进行表征,结果显示纤维膜中纤维的直径为30～50nm,表面有丰富的微孔。以PEI-PVDF-g-PAA纤维膜为吸附材料对模拟活性艳红X-3B染料废水进行吸附,并研究其吸附动力学、吸附等温模型和吸附热力学,结果表明:PEI-PVDF-g-PAA纤维膜的吸附效果远远大于纯PVDF纤维膜和PVDF-g-PAA纤维膜。在活性艳红X-3B溶液的初始质量浓度为150mg/L、pH=1、吸附材料用量为0.015g时,吸附70min后达到平衡,平衡吸附量为494.95mg/g,PEI-PVDF-gPAA纤维膜对活性艳红X-3B的吸附过程满足拟二级动力学模型和Langmuir吸附等温模型,说明PEI-PVDF-g-PAA纤维膜对活性艳红...     

pH值对Ca2+、La3+和Al3+与拟南芥钙调素竞争结合作用的影响

利用Tb3+荧光光谱,通过Tb·CaM系统的特征光谱在加入Ca2+、La3+和Al3+前后荧光强度的改变,研究了pH值对Ca2+、La3+和Al3+与拟南芥钙调素 (CaM)竞争结合作用的影响.结果表明,在中性条件下,金属离子与Tb·CaM系统中Tb3+的竞争能力强弱顺序为:La3+＞Ca2+＞Al3+,与钙调素的结合力为:Tb3+＞ La3+＞Ca2+＞Al3+.在pH值等于4.5的酸性条件下,Ca2+、La3+和Al3+与Tb3+的竞争结合能力较中性条件下弱,同时,稀土在酸性条件下的竞争结合力大于Ca2+和Al3+,Al3+与CaM竞争结合能力在酸性条件下大于Ca2+.竞争实验的结果从分子水平上证实了金属离子可取代Ca·CaM中的Ca2+与钙调素产生竞争性结合,模拟Ca2+ 4·CaM的行为,且pH值对金属离子与钙调素竞争结合力产生一定影响,揭示了胞外钙调素在酸性和金属离子浓度较高的生理条件下生物效应可能的分子机制.     

Er-modified MnOx for selective catalytic reduction of NOx with NH3 at low temperature: Promoting effect of erbium on catalytic performance

Various Er modified MnO_x catalysts were synthesized using co-precipitation approach and tested in the selective catalytic reduction of NO_x by ammonia(NH₃-SCR).Catalysts were analyzed with various characterization techniques,and it is found that the doping of Er can enormously enhance the catalytic performance of MnOx catalyst.MnEr_0.1 demonstrates advantageous catalytic performance in the NH₃-SCR reaction owing to rich surface acidic sites,hi...     

Construction of bimetallic Pt-Pd/CeO2-ZrO2-La2O3 catalysts with different Pt/Pd ratios and its structure-activity correlations for three-way catalytic performance

A series of Pt-Pd bimetallic catalysts supported on CeO₂-ZrO₂-La₂O₃ mixed oxides were synthesized through the conventional impregnation method.Three-way catalytic performance evaluations along with detailed physio-chemical characterizations were carried out to establish possible structure-activity correlations.Results show that on the one hand,different Pt/Pd ratios can strongly affect the TWC behaviors of Pt-Pd/CZL catalysts by modulating the synergis...     

Ga3+ as a functional substitute for Fe3+: preparation and characterization of the Ga3+Fe2+ and Ga3+Zn2+ forms of bovine spleen purple acid phosphatase

A general method has been developed that allows the specific substitution of both iron atoms in the enzyme bovine spleen purple acid phosphatase (BSPAP), which possesses a dinuclear iron center at the active site. The approach is demonstrated by the preparation and characterization (atomic absorption spectrometry, enzyme kinetics, optical spectroscopy, and electron paramagnetic resonance spectroscopy) of two metal-substituted forms in which the ferric iron has been replaced by Ga3+: Ga3+Fe2+-BSPAP and Ga3+Zn2+-BSPAP. Both forms are colorless but exhibit enzymatic activity comparable to that of the native Fe3+Fe2+-BSPAP. Small but consistent changes in kinetics parameters and pH profiles were detected both upon substitution of Fe3+ by Ga3+ and upon substitution of Fe2+ by Zn2+. These results constitute the first evidence that the diamagnetic Ga3+ ion can serve as a functional analogue of Fe3+ in an enzyme, and suggest a novel approach for the study of the role of Fe3+ in other iron enzymes.     

Mg~（2＋）,Ca~（2＋）,Ba~（2＋）离子部分取代对SrAl_2O_4：Eu~（2＋）,Dy~（3＋）晶体结构和发光性能的影响

采用高温固相反应法制备了Sr0.9M0.1Al2O4：Eu2＋,Dy3＋（M=Mg,Ca,Ba）长余辉发光材料,并对其晶体结构、光谱性质、余辉特性进行了分析.X射线衍射测试结果表明,Mg2＋,Ca2＋,Ba2＋离子部分取代SrAl2O4基质中的Sr后,基质晶体结构并没有发生改变.光谱测试结果表明,Mg2＋,Ca2＋,Ba2＋取代后发光材料的激发光谱都是一个从250~450 nm范围内的宽激发带,在266nm,320nm,360nm,416 nm处各有一个激发峰.发射光谱中Mg2＋和Ba2＋的取代使波长出现蓝移,而Ca2＋的取代使波长出现红移.余辉测试结果表明,Ca2＋取代后的余辉时间长于Mg2＋和Ba2＋的取代.     

Synthesis,crystal structure and photoluminescence properties of novel double perovskite La2CaSnO6:Eu3+ red-emitting phosphors

A series of new double perovskite La_2–xEu_xCaSnO₆ (0 ≤ x ≤ 0.8) red phosphors were synthesized by traditional solid-state reaction. The phase, microstructure, photoluminescence (PL) properties, quantum efficiency, and thermal stability of the phosphors were investigated. La₂CaSnO₆ matrix has a monoclinic double perovskite structure with space group P2₁/n. Under near-ultraviolet (UV) light at 395 nm, La_2–xEu_xCaSnO₆ phosphors exhibit the most typical red emission peak at 614 nm, which corresponds to ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺. The optimum Eu³⁺ doping content is attained at x = 0.5, and the La_1.5Eu_0.5CaSnO₆ phosphor shows a moderate quantum efficiency (32.3%) and high color purity (92.2%). Besides, the temperature-dependent spectrum of the phosphor was studied. The emission intensity of Eu³⁺ at 423 K decreases to 70.94% of the initial intensity at 303 K, and the activation energy ΔE is estimated to be 0.232 eV, suggesting that the phosphors possess good thermal stability. The fabricated w-LED based on the phosphors has higher R_a (89), lower CCT (4539K), and better chromaticity coordinates (0.371, 0.428). These results prove that the Eu³⁺-doped La₂CaSnO₆ red phosphor has great potential applications in w-LEDs.     

Effect of Li+ ion concentration on upconversion emission and temperature sensing behavior of La2O3:Er3+ phosphors

The effects of Li~+ co-doping concentration on the structure, upconversion luminescence and temperature sensing behavior of Er~(3+):La_2O_3 phosphors were investigated. X-ray diffraction and scanning electron microscopy observations reveal that Li~+ ion co-doping can change the lattice parameter of La_2O_3 host and increase the particle size of the samples. The optical investigation shows that co-doping of Li~+ ions can enhance the upconversion emission of Er~(3+) ions in La_2O_3 matrix effectively. Most importantly, the temperature sensing sensitivity of the samples is found to be dependent on Li~+ co-doping concentration,when the emission intensity ratio of the(~2H_(11/2)→~4 I_(15/2)) and(~4 S_(3/2)→~4 I_(15/2)) transitions of Er~(3+) is chosen as the thermometric index. Both of the optimum upconversion luminescence and temperature sensing sensitivity are obtained for 7 mol% Li~+ co-doped sample. When the Li~+ concentration is beyond 7 mol%,both the quenching in upconversion intensity and the degradation of temperature sensitivity are observed, which may be due to the serious distortion in local crystal field around Er~(3+) ions caused by the excess Li~+ ions.     

Comparison of the effects of Ca2+ and those of Mg2+ and La3+ on endplate currents in mouse interosseus muscles

Intravascular ultrasound imaging (IVUS) is a new method that permits in vivo visualization of central venous catheters with hitherto unknown image resolution. It provides information not only about thrombus formation, but also about catheter movement, catheter malposition, and vessel wall injuries. In the present investigation the method was applied to evaluate the frequency of thrombus formation on double-lumen hemodialysis catheters and its significance for catheter malfunction. In 14 patients who had a double-lumen hemodialysis catheter for temporary or long-term vascular access, IVUS of the catheter and the mediastinal vein stems was performed. Mean indwelling duration at the time of the ultrasound investigation was 101 days (range. 3 to 730 days; median, 58 days). Four patients had catheter-related thrombotic complications: IVUS failed to detect an intracatheter thrombus in one case; a catheter thrombus and superior vena cava stenosis were found in a catheter with normal function in one case; in one case with catheter malfunction, a combined catheter-mural thrombus was found; and in the remaining case, a catheter thrombus and a mural superior vena cava thrombus were found in a patient with normal catheter function and pulmonary emboli. Thus, two of 12 patients with well-functioning catheters (16%) had thrombotic complications demonstrated by IVUS, and one of two patients with catheter malfunction had thrombus identified by IVUS. It is concluded that thrombus formation is less likely in patients without signs of catheter malfunction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Promoting effect of microwave irradiation on CeO_2-TiO_2 catalyst for selective catalytic reduction of NO by NH_3

In this work we prepared several CeO₂-TiO₂ catalysts for the NH₃-SCR reactionusing co-precipitation with assistance of microwave irradiation. The catalytic NH₃-SCR activities over CeO₂-TiO₂ catalysts at low temperatures are largely enhanced by the treatment of microwave irradiation, the operation temperature window is also broadened. For better understanding the promotion mechanism, the catalyst prepared by conventional co-precipitation with and without microwave irradiation treatment was characterized with H₂-TPR, NH₃-TPD, XPS, XRD and BET. Microwave irradiation treatment accelerates the crystallite rate of CeO₂-TiO₂ catalysts, and greatly enlarges their surface area by adjusting their microstructures. The resistance to SO₂ and H₂O is also improved via regulating the hierarchical pore structure by the microwave irradiation. Microwave irradiation treatment can also improve the redox property and increase the acid sites over the catalyst surfaces. The result of in situ DRIFTS suggests that the microwave irradiation treatment generates more Brønsted acid sites on CeO₂-TiO₂-2 h catalyst, helpful in SCR reactions. XPS results show that after microwave irradiation on the CeO₂-TiO₂ catalysts, the surface demonstrates an elevated concentration of chemisorbed oxygen, consequently leading to better oxidation of NO to NO₂. Additionally, the molar ratio of Ce³⁺/Ce⁴⁺ has been elevated after being treated by microwave irradiation, a vital factor in enhancing the NH₃-SCR activities.