Full-profile fitting of emission spectrum to determine transition intensity parameters of Yb~(3+):GdTaO_4

The Judd-Ofelt theoretic transition intensity parameters A_(tp)~k of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence.It is very difficult to determine them with emission or absorption spectra for a long time.A "full profile fitting" method to obtain A_(tp)~k in solids with its emission spectrum is proposed,in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability,line profile function,instrument measurement constant and transition center frequency or wavelength,and the whole experimental emission spectrum is the sum of all transitions.In this way,the emission spectrum is expressed as a function with the independent variables intensity parameters A_(tp)~k,full width at half maximum(FWHM) of profile functions,instrument measurement constant,wavelength,and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered.The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting A_(tp)~k and other parameters.Employing this method obviates measurement of the absolute emission spectrum intensity.It also eliminates dependence upon the number of emission transition peaks.Every experiment point in emission spectra,which usually have at least hundreds of data points,is the function with variables A_(tp)~k and other parameters,so it is usually viable to determine A_(tp)~k and other parameters using a large number of experimental values.We applied this method to determine twenty-five A_(tp)~k of Yb~(3+) in GdTaO_4.The calculated and experiment energy lifetimes,experimental and calculated emission spectrum are very consistent,indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum.The calculated emission cross sections of Yb~(3+):GdTaO_4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.     

用于液体激光介质的Nd~(3+)离子掺杂氟化镧纳米颗粒的制备与性能表征

设计并合成了掺杂不同Nd3+离子浓度的氟化镧纳米颗粒,并用油酸进行了表面修饰,使得这类纳米颗粒可分散于常见的有机溶剂中形成透明、均一、稳定的溶液。对纳米颗粒的结构、晶相以及发光性能进行了表征。固体和溶液材料在1 060 nm都有强的发射峰,说明纳米晶格可有效地保护Nd3+离子免受外界环境对发光的猝灭影响。纳米颗粒有机溶液的吸收损耗和散射损耗测试结果表明,其总损耗系数能够满足激光介质材料的损耗要求,为该材料的实用化打下了基础。     

Screening and interlayer coupling in multilayer MoS2

The two‐dimensional layered semiconducting di‐chalcogenides are emerging as promising candidates for post‐Si‐CMOS applications owing to their excellent electrostatic integrity and the presence of a finite energy bandgap, unlike graphene. However, in order to unravel the ultimate potential of these materials, one needs to investigate different aspects of carrier transport. In this Letter, we present the first comprehensive experimental study on the dependence of carrier mobility on the layer thickness of back‐gated multilayer MoS₂ field‐effect transistors. We observe a non‐monotonic trend in the extracted effective field‐effect mobility with layer thickness which is of relevance for the design of high‐performance devices. We also discuss a detailed theoretical model based on Thomas–Fermi charge screening and interlayer coupling in order to explain our experimental observations. Our model is generic and, therefore, is believed to be applicable to any two‐dimensional layered system.

     

钙钛矿Mn基氧化物的电子顺磁共振行为的实验研究

借助电子顺磁共振技术,对Mn³⁺/Mn⁴⁺=2∶1和1∶1的两个典型体系 在居里温度T_C以上温区的顺磁行为进行了实验研究.实验表明,存在一特征温度 T_min,通过该温度将T_C以上的磁行为分成两个明显可区分的温区： 在T_min以上,共振谱由一对称的单线构成,Lande 因子g值与温度无关且接近 自由电子的值(～20023),线宽随温度呈线性变化等;而在T_{min关键词： 稀土锰氧化物 电子顺磁共振 交换变窄 自旋-自旋相互作用 自旋-晶格相互作用}     

X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Hydrogen evolution reaction on Pt and Ru in alkali with volmer-step promotors and electronic structure modulators

Alkaline water electrolysis despite having a variety of choices for anodic oxygen evolution reaction (OER) catalysts out of non-precious metals suffers significantly due to the poor kinetics of cathodic hydrogen evolution reaction (HER) even with the state-of-the-art Pt and equally active Ru. The Volmer-step (water dissociation (WD) coupled proton adsorption) of alkaline HER is mostly the rate-determining step (RDS) and costs most of the work required. In this review, recent developments in improving the HER kinetics of Pt and Ru with Volmer-step promotors and electronic structure modulators have been comprehensively analyzed and critically presented with the challenges and prospects.     

Catalytic Selective Dihydrosilylation of Internal Alkynes Enabled by Rare‐Earth Ate Complex

Hydrosilylation of alkynes generally yield vinylsilanes, which are inert to the further hydrosilylation because of the steric effects. Reported here is the first successful dihydrosilylation of aryl‐ and silyl‐substituted internal alkynes enabled by a rare‐earth ate complex to yield geminal bis‐ and tris(silanes), respectively. The lanthanum bis(amido) ate complex supported by an ene‐diamido ligand proved to be the ideal catalyst for this unprecedented transformation, while the same series of yttrium and samarium alkyl and samarium bis(amido) ate complexes exhibited poor activity and selectivity, indicating significant effects of the ionic size and ate structure of the rare‐earth catalysts.     

Rare-earth metal derivatives supported by aminophenoxy ligand: Synthesis,characterization and catalytic performance in lactide polymerization

A library of rare-earth metal derivatives supported by an aminophenoxy ligand was prepared and their catalytic performance in lactide polymerization was investigated. It was found that the synthetic strategy had a profound effect on the formation of aminophenoxy rare-earth metal complexes. Amine elimination between Ln[N(SiMe₃)₂]₃(μ-Cl)Li(THF)₃ (Ln = Yb, Y) and 1 equiv. of the aminophenol [HONH] ([HONH] = ο-OCH₃-C₆H₄NHCH₂(3,5-^tBu₂-C₆H₂-2-OH)) in toluene gave the unexpected heterobimetallic bis(aminophenoxy) rare-earth metal complexes [ON]₂LnLi(THF)₂ (Ln = Yb ( 1 ), Y ( 2 )). When the reactions were carried out in THF and TMEDA, amine elimination produced the aminophenoxy rare-earth metal amide complexes {[ON]LnN(SiMe₃)₂}₂ (Ln = Yb ( 5 ), Y ( 6 )) in ca 85% isolated yields. Complexes 5 and 6 could also be obtained from salt metathesis reaction of {[ON]LnCl(THF)}₂ (Ln = Yb ( 3 ), Y ( 4 )) with NaN(SiMe₃)₂ in a 1:2 molar ratio. In addition, treatment of complexes 3 and 4 with NaOAr (Ar = &bond;C₆H₄-4-^tBu) and (SiMe₃)₂NC(NPrⁱ)₂Na in 1:4 and 1:2 molar ratios provided the corresponding aminophenoxy rare-earth metal derivatives {[ON](μ-OAr)Ln(μ-OAr)Na(THF)₂}₂ (Ln = Yb ( 7 ), Y ( 8 )) and {[ON]Ln[(ⁱPrN)₂CN(SiMe₃)₂]}₂ (Ln = Yb ( 9 ), Y ( 10 )), respectively. These complexes were fully characterized, and their molecular structures were determined using single-crystal X-ray diffraction. Polymerization experiments showed that complexes 1 , 2 , 5 , 6 , 9 and 10 were highly active for the ring-opening polymerization of l -lactide in toluene, and complex 1 promoted l -lactide polymerization in a controlled fashion. The polymerization of rac-lactide initiated by the neutral aminophenoxy rare-earth metal complexes 5 , 6 , 9 and 10 in THF afforded heterotactic polymers.     

Bipolar Electrochemistry Exfoliation of Layered Metal Chalcogenides Sb2S3 and Bi2S3 and their Hydrogen Evolution Applications

Efficient exfoliation and downsizing of Sb₂S₃ and Bi₂S₃ layered compounds by using scalable bipolar electrochemistry on their suspensions in aqueous media are here demonstrated. The resulting samples were characterized in detail by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy; their electrochemistry toward hydrogen evolution was also investigated. Hydrogen evolution ability of exfoliated Sb₂S₃ and Bi₂S₃ was investigated and compared to the bulk counterparts.     

Syntheses,molecular structures,and thermal decomposition of cyclopentadienyldicarbonylmanganese chalcogenide derivatives

Transmetallation of the dichalcogenide complexes [CpMn(CO)₂]₂(-X₂) (X = S or Se) with M(CO)₅(thf) (M = Cr or W) afforded new heterometallic complexes CpMn(CO)₂(-Se₂)Cr(CO)₅, CpMn(CO)₂(-Se₂)[Cr(CO)₅]₂, CpMn(CO)₂(-X₂)[W(CO)₅]₂ (X = S or Se), and CpMn(CO)₂(-Se₂)[Cr(CO)₅][W(CO)₅]. According to the X-ray diffraction data, their molecular structures contain the cyclic MnX₂ fragments coordinated by one or two M(CO)₅ groups via the X atoms. Study of thermal decomposition of the manganese complexes with different Mn : M : X ratios (M = Cr, W; X = S, Se, Te) by differential scanning calorimetry (DSC) and thermogravimetry demonstrated that this process took place at rather low temperatures (100—400 °C) and was accompanied by complete elimination of the CO groups followed by elimination of the Cp groups. At any metal to chalcogen ratio, the resulting inorganic chalcogenides contained no impurities of metal oxides and carbides.