Synthesis and luminescence properties of Mn4+-dopantCa14Zn6Ga10−xAlxO35 solid solution

Mn~(4+)-activated oxide phosphors,owing to their desirable spectral features,eco-friendly and low cost,are emerging as a new class of non-rare-earth red phosphors for warm white LEDs.However,these phosphors possess low photoluminescence quantum efficiency excited by blue chip currently.Herein we report an isostructural solid solution of Ca_(14)Zn_6Ga_(10-x)Al_xO_(35):0.15Mn~(4+)(0≤x≤10)synthesized by a traditional solidstate reaction route.The microstructure and luminescent performance of this red-emitting phosphor are investigated in detail with the aids of X-ray diffraction,diffuse reflection spectra,photoluminescence spectra/decay/QE,and temperature-dependent PL/QE measurements.Blue shift of energy peaks of~4A_2→~4T_1and~4A_2→~4T_2transition is illustrated by the Tanabe–Sugano diagram and the configurational coordinate diagram.The crystal field strength(Dq)and the Racah parameters(B and C)are carefully calculated to estimate the nephelauxetic effectβrespectively.Particularly we achieve external and internal quantum efficiencies as high as26.1%and 40.3%for Ca_(14)Zn_6Ga_6Al_4O_(35):0.15Mn~(4+)excited by 466 nm,the highest one ever reported in Mn~(4+)activated oxide phosphors under the similar condition.     

Structural and optical properties of Zn1−xNixTe thin films prepared by electron beam evaporation technique

Zn1-xNixTe thin films with different composition(x=0.0, 0.05, 0.10, 0.15 and 0.20) were deposited on glass substrate by electron beam evaporation technique followed by its characterization using advanced structural and optical analysis techniques. Structural properties of the prepared thin films were studied by X-ray diffraction(XRD). The XRD patterns revealed that the binary compounds transformed into a ternary compound with cubic structure having preferred orientation along the c-direction with(111) planes. Composition analysis of the films was determined by energy dispersive analysis of X-rays(EDAX) and found to be in agreement with the precursor composition. Optical properties such as extinction coefficient(k) and band gap energy of these films were examined by using a spectroscopic ellipsometer. It was found that the extinction coefficient(k) increased with the addition of Ni content in the alloy. In comparison, the band gap energy was also determined by using transmission spectra and found to be agreed with that of the ellipsometric results. These analyses confirm that the band gap energy decreases with the increase of Ni content in the alloy.     

Microstructures and mechanical properties of as-extruded Mg–5Sn–1Zn–xAl(x=1, 3 and 5) alloys

As-extruded Mg–5Sn–1Zn–xAl alloys(x=1, 3, and 5) were fabricated by hot extrusion. The experimental results revealed that the yield strength of alloys initially decreased and then increased with the increase of Al content. These changes were mainly attributed to the difference in crystallographic texture and volume fractions of second phases. The ultimate tensile strength, yield strength, and elongation of the alloys were greater than 310 MPa, 227 MPa, and 11%, respectively. The strain hardening ability of the alloys was also discussed.     

Improvements of dielectric properties of Cu doped LaTiO_(3+δ)

The ceramic composites of Cu-doped La_(1-x )Cu_x TiO_(3+δ)(x=0.05, 0.15, 0.3, 0.5) were synthesized by conventional solid-state reaction. The complex dielectric properties of the composites were investigated as a function of temperature(77 K ≤T≤ 320 K) and frequency(100 Hz ≤ f ≤1 MHz) separately. In all composites, the dielectric constants increase monotonously and the dielectric loss undulates with temperature. And it is clearly observed that extraordinarily high low-frequency dielectric constant(～10~4)appear at room temperature in La_0.5Cu_0.5TiO_(3+δ), which is 100 times larger than that of La_0.95Cu_0.05 TiO_(3+δ). Interestingly, the dielectric constants increase remarkably with the doped Cu contents, meanwhile the dielectric loss for all samples is ideal lower than 1 at room temperature in the measured frequency range. By means of complex impedance analysis, the improvements of dielectric properties are attributed to both bulk contribution and grain boundary effect, in which the bulk polaronic relaxation and the Maxwell–Wagner relaxation due to grain boundary response are heightened remarkably with the high doped Cu contents.     

Influence of Ga-doping on the thermoelectric properties of Bi(2−x)GaxTe2.7Se0.3 alloy

Bi(2-x)GaxTe2.7Se0.3(x=0, 0.04, 0.08, 0.12) alloys were fabricated by vacuum melting and hot pressing technique. The structure of the samples was evaluated by means of X-ray diffraction. The peak shift toward higher angle can be observed by Ga-doping. The effects of Ga substitution for Bi on the electrical and thermal transport properties were investigated in the temperature range of 300–500 K. The power factor values of the Ga-doped samples are obviously improved in the temperature range of 300–440 K. Among all the samples, the Bi(2-x)GaxTe2.7Se0.3(x=0.04) sample showed the lowest thermal conductivity near room temperature and the maximum ZT value reached 0.82 at 400 K.     

Microstructure, crystalline phase and electrical properties of Li0.06(Na0.5K0.5)0.94Nb(1−2x/5)Mg x O3 lead-free piezoelectric ceramics

MgO-modified Li_0.06(Na_0.5K_0.5)_0.94NbO₃ (L₆NKN) lead-free piezoelectric ceramics were synthesized by normal sintering at a relatively low temperature of 1000°C. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sinterability of the L₆NKN ceramics. X-ray diffraction analysis indicates that the morphotropic phase boundary (MPB) separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content (x) from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant (d ₃₃=238 pC/N), planar electromechanical coupling coefficient (k _p=41.5%), relative dielectric constant (? _r=905), and remanent polarization (P _r=38.3 μC/cm²) are obtained from the specimen with x=0.5at%, which suggests that the Li_0.06(Na_0.5K_0.5)_0.94Nb_(1?2x/5)Mg _x O₃ (x=0.5at%) ceramic is a promising lead-free piezoelectric material.     

Correlation between the glass-forming ability and activation energy of crystallization for Zr75−x Ni25Al x metallic glasses

The thermal stability and the kinetics of glass transition and crystallization for Zr_75?x Ni₂₅Al _x (x = 8–15) metallic glasses were investigated using differential scanning calorimetry (DSC) under continuous heating conditions. The apparent activation energy of glass transition rises monotonously with the Al content increasing; the activation energy of crystallization increases with Al changing from 8at% to 15at%, and then decreases with Al further up to 24at%, which exhibits a good correlation to the thermal stability and the glass-forming ability (GFA). The Zr₆₀Ni₂₅Al₁₅ metallic glass with the largest supercooled liquid region and GFA possesses the highest activation energy of crystallization. The relation between the thermal stability, GFA and activation energy of crystallization was discussed in terms of the primary precipitated phases.     

Optical properties of NdxGd1−xAl3(BO3)4 crystal

The optical properties of Nd x Gd 1-x Al-3(BO-3)-4 (NGAB) crystal are reported. The refractive index of it were mesured by V_prism method. The absorption spectra and the flourescence specra of NGAB were also obtained. The optical parameters of NGAB were calculated following J_O theory, the three optical parameters are Ω 2 =1 805×10 -20 , Ω 4=1 85×10 -20 , Ω 6=3 793×10 -20 (RMS=1 4×10 -7 ) and β c( 4F 3/2 → 4I 11/2 ) is about 0 53.     

Effect of KNbO3 content on the crystal structure and electrical properties of (1 − x)PbZr0.54Ti0.46O3-xKNbO3 piezoelectric ceramics

(1 ? x)PbZr_0.54Ti_0.46O₃-xKNbO₃ (0 ≤ x ≤ 25mol%) (abbreviated as PZT-xKN) piezoelectric ceramics were successfully fabricated by a traditional sintering technique at 1225°C for 30 min. The influence of KNbO₃ content on the crystal structure and electrical properties of the PZT-xKN piezoelectric ceramics was studied. Samples with 0 ≤ x ≤ 0.20 show a pure perovskite structure, indicating that all KNbO₃ diffused into the crystal lattice of PZT to form a single solid solution in this compositional range. A second Pb₃Nb₄O₁₃ phase is observed in the PZT-0.25KN sample, showing that the maximum solid solubility of KNbO₃ in PZT matrix ceramic is less than 25mol%. Compared with pure PZT piezoelectric ceramics, samples containing KNbO₃ have smaller crystal grains. PZT-0.15KN exhibits excellent piezoelectric properties with d ₃₃ = 209 pC/N.     

(Zn.Cd)S:Ag光解水放氢的研究

本文报导了利用掺有或不掺有KI的(Zu·Cd)S:Ag粉末作吸光材料,在钨丝灯下光解水放氢的某些结果。由于该反应是在自然条件下进行,也就是说不需要用缓冲剂把反应液调到一定的pH值,因此反应体系比较简单,除水之外不存在任何具它氢源,故所得之氢必然来自于水。     

Effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of La1−xMgxNi3.5 (x=0.20, 0.23, 0.25 at%) alloys

The effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of the annealed La_(1-x) Mg_x Ni_3.5(x=0.20, 0.23, 0.25 at%) alloys have been studied. All the samples were mainly composed of(LaMg)_2Ni_7,(LaMg)Ni_3, and LaNi_5 phases. Mg substitution for La changed the phase abundance, but did not change the constitution of all phases, which is con fi rmed by the results of backscattered SEM images and EDS analysis. The P–C isotherms indicated that the La_(1-x) Mg_x Ni_3.5alloys reversibly absorbed and desorbed hydrogen smoothly at 298 K. The hydrogen absorption cyclic stabilities of La_(1-x) Mg_x Ni_3.5alloy after 5 hydrogen absorption/desorption cycles reached the maximum values of91.9% and 96.0% at 298 K and 323 K, respectively. The hydrogen desorption capacity and plateau pressure for the La_(1-x) Mg_x Ni_3.5alloy reached the maximum values of 1.055 H/M and 0.074 MPa, respectively. The desorption capacities of La_(1-x) Mg_x Ni_3.5reached 0.193 H/M and 0.565 H/M in the fi rst minute at 298 K and 323 K, respectively. Electrochemical property measurement indicated that La_(1-x) Mg_x Ni_3.5(x=0.20,0.23, 0.25 at%) alloys possessed excellent activation capability and were completely activated within3 cycles. Discharge capacities of La_(1-x) Mg_x Ni_3.5alloys reached 378.2 m A h/g(x = 0.20 at%), 342.7 m A h/g(x = 0.23 at%), and 369.6 m A h/g(x = 0.25 at%), respectively. Moreover, energy density of La_(1-x) Mg_x Ni_3.5alloy was much larger than that of La_0.80Mg_0.20Ni_3.5 alloy and nearly approaches the maximum value of La0.75Mg0.25Ni3.5. Thus, the La_(1-x) Mg_x Ni_3.5alloy exhibits optimum comprehensive properties of hydrogen storage and electrochemistry.     

Hydrogen absorption properties of amorphous (Ni0.6Nb0.4−yTay)100−xZrx membranes

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun(Ni_(0.6)Nb_(0.4-y)Ta_y)_(100-x)Zr_x with y=0, 0.1 and x=20, 30 was studied. The result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T 400 °C, even in a hydrogen atmosphere(1-10 bar), the amorphous structure was retained. The crystallization process was characterized by differential thermal analysis and the activation energy of such process was obtained. The hydrogen absorption properties of the samples in their amorphous state were studied by the volumetric method,and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear change of the hydrogen solubility was observed with the variation of the Zr content. The values of the hydrogenation enthalpy changed from ~37 k J/mol for x=30 to ~9 k J/mol for x=20. The analysis of the volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum of energy levels.     

晶体结构对(Zn,Cd)S:Cu电致发光材料发光性能的影响

采用X射线衍射法定量测定了不同Cd2+含量下,(Zn,Cd)S:Cu,Cl电致发光粉的晶体结构成分.发现随着Cd2+的增加,材料中立方结构的含量逐渐减少,发光光谱向长波方向移动,而且亮度逐渐降低.利用相变使材料结构由六角结构向立方结构转变,大幅度提高了材料的发光亮度.     

Mossbauer spectra and magnetic properties of amorphous (Fe_(1-x)Co_x)_(77.5)Nd_4B_(18.5) alloys

本文研究了非晶合金(Fe_(1-x)Co_x)_(77.5)Nd_4B_(18.5)(0≤X≤1.O)的~57Fe穆斯堡尔谱和磁的特性.假设Co原子磁矩保持1.21μB,则Fe原子磁矩随着含量X的增加而增加.Fe磁矩的增加与Fe的平均超精细场的增加是一致的.当Co含量在x=0.7时居里温度达最大值,在室温下,晶体化的FeCoNdB合金在Co含量较小时有高的矫顽场和能积.     

Structural,morphological, and optical properties of tin(Ⅳ) oxide nanoparticles synthesized using Camellia sinensis extract: a green approach

Tin oxide (SnO2) nanoparticles were cost-effectively synthesized using nontoxic chemicals and green tea (Camellia sinensis) extract via a green synthesis method.The structural properties of the obtained nanoparticles were studied using X-ray diffraction,which indicated that the crystallite size was less than 20 nm.The particle size and morphology of the nanoparticles were analyzed using scanning electron microscopy and transmission electron microscopy.The morphological analysis revealed agglomerated spherical nanoparticles with sizes varying from 5 to 30 nm.The optical properties of the nanoparticles' band gap were characterized using diffuse reflectance spectroscopy.The band gap was found to decrease with increasing annealing temperature.The O vacancy defects were analyzed using photoluminescence spectroscopy.The increase in the crystallite size,decreasing band gap,and the increasing intensities of the UV and visible emission peaks indicated that the green-synthesized SnO2 may play future important roles in catalysis and optoelectronic devices.     

Structural,morphological,and optical properties of tin(Ⅳ) oxide nanoparticles synthesized using Camellia sinensis extract: a green approach

Tin oxide(SnO_2) nanoparticles were cost-effectively synthesized using nontoxic chemicals and green tea(Camellia sinensis) extract via a green synthesis method. The structural properties of the obtained nanoparticles were studied using X-ray diffraction, which indicated that the crystallite size was less than 20 nm. The particle size and morphology of the nanoparticles were analyzed using scanning electron microscopy and transmission electron microscopy. The morphological analysis revealed agglomerated spherical nanoparticles with sizes varying from 5 to 30 nm. The optical properties of the nanoparticles' band gap were characterized using diffuse reflectance spectroscopy. The band gap was found to decrease with increasing annealing temperature. The O vacancy defects were analyzed using photoluminescence spectroscopy. The increase in the crystallite size, decreasing band gap, and the increasing intensities of the UV and visible emission peaks indicated that the green-synthesized SnO_2 may play future important roles in catalysis and optoelectronic devices.     

Synthesis, structure and photo-physical properties of coordination polymer of Pr( Ⅲ ), Yb( ⅢⅢ )

采用水热合成的方法,以肉桂酸为配体,合成了2种Ln(Ⅲ)的配合物[Pr(C9 H7O2)3]n(1)和[Yd(C9 H7O2)3]n(2) (C9H7O2=肉桂酸根),通过X—射线单晶衍射仪确定了配合物1和2的晶体结构.结构分析表明,1和2均是以(C9 H7O2)为桥连配体而形成的1D无限链状结构,但不同构.1是三斜晶系,R3c空间群,晶胞参数为:a=2.2630(4)nm,b=2.2630(4) nm,c=0.787 6(3) nm,α=90°,β=90°,γ=120°;2是单斜晶系,P2(1)空间群,晶胞参数为:a=1.15336(16) nm,b=0.78421(11) nm,c=1.30222(18) nm,α=90°,β=94.371(2)°,γ=90°.在室温下测定了2种配合物固态粉末的IR光谱,UV-Vis-NIR光谱以及荧光激发和发射光谱,并进行了分析指认.这2种配合物IR光谱的主要谱带极为相似,它们的UV-ViS-NIR吸收光谱均表现出配体的π→π(')跃迁吸收带和稀土离子的f-f特征吸收带.此外,重点讨论了它们的发光性质,尤其是配合物2在NIR区表现出Yb(Ⅲ)的特征发射.     

Mesoporous β-Co(OH)_2 nanowafers and nanohexagonals obtained synchronously in one solution and their electrochemical hydrogen storage properties

A water/oil two-phase solution strategy has been developed for the synthesis of various β-Co(OH)_2 nanostructures. More importantly, two different morphologies of β-Co(OH)_2:mesoporous nanowafers and nanohexagons were successfully obtained through one reaction. Furthermore, the special mesoporous of β-Co(OH)_2 nanowafers and nanohexagons exhibited excellent electrochemical hydrogen storage capacities and cycling stability. The maximum capacity reached 265.9 and 215.7 mA hg~(-1) at room temperature, respectively.After 70 cycles, the discharging capacities of the electrode still remain above 218.2 and 175.4 mA hg~(-1), which indicates that the as-prepared mesoporous β-Co(OH)_2 nanowafers have a strong resistance against oxidation and corrosion. These results indicates that the mesoporous β-Co(OH)_2 nanowafers and nanohexagons may be potentially applied for electrochemical hydrogen storage.     

Preparation of (R)-and (S)-2-Allyl-1,3,2-Dinaphtho(α,β)[d.f]dioxaborepin and Their Reactions with Aldehydes

0　IntroductionEnantiopure 1,1′ bi 2 naphtholspossessingC2 chiralityhaveprovedtobeversatilechiralauxiliariesinanumberofasym metricreactions[1 \|6] .Althoughsomeboroncompoundsofthemhavebeenprepared[7 1 6] ,chemistryoftheirallylboranederivativeshasneverbeenreported .Toexplorepossibilityofapplyingseven memberedcyclicchrialallylboronateesterstoasymmetricsynthesisofchiralβ alkenylalcohols,whichareimportantintermediateinthepreparationofopticallyactivenaturalproducts,werecentlyat temptedtosynthesi…     

Preparation of ( )-1-Phenylethylamine by Optical Resolution of Racemic 1-Phenylethylamine with a Chiral Biopolymer,Casein

1 Results It has been reported that crystalline form racemates can be resoluted by various methods[1],but for optical resolution of liquid form racemates,the method is limited in chromatograph.So chiral compounds cannot be obtained on large scale by such method.In our previous paper,( )-3-chloro-1,2-propanediol has been obtained by optical resolution of its racemata (liquid) with a chiral biopolymer,casein[2].