Measurement of atomic L shell fluorescence (ω1, ω2, ω3) and Auger (a1, a2 and a3) yields for some elements in the atomic number range 59≤Z≤85

A comprehensive set of theoretical Coster–Kronig and fluorescence yields are presented for atomic numbers 18≤Z≤100. These quantities are based on ab initio relativistic calculations. Agreement with experimental values is fair for ω₁ and generally good for ω₂, ω₃ (Z≥54) [1]. Therefore, atomic L shell fluorescence (ω₁, ω₂, ω₃) and Auger yields (a₁, a₂ and a₃) for some elements in the atomic number range 59≤Z≤85 were determined. These selected measured semi-empirical values were also fitted by least squares to polynomials in the Z of the form ∑_na_nZⁿ and compared with theoretical and with earlier fitted values.     

CdTe水溶性量子点的合成表征及生物毒性测定——一个化学生物学实验

本实验以反应时间为变量,一步水相法合成了具有不同粒径的CdTe量子点。通过紫外-可见吸收光谱和荧光光谱表征不同反应时间得到的量子点,并计算其粒径、浓度以及荧光量子产率。取表征最优的量子点组次,配制成不同浓度,与酵母混合培养,用Biomass法测定CdTe量子点生物毒性。该实验涵盖无机合成相关知识,涉及分析表征方法应用以及量子点对生物细胞活性的影响,化学与生物学科交叉融合,有助于学生科研能力的培养与实验综合能力的提升。     

Lead-Free,Water-Stable A3Bi2I9 Perovskites: Crystal Growth and Blue-Emitting Quantum Dots [A=CH3NH3+, Cs+, and (Rb0.05Cs2.95)+]

Despite the great success in the increase in the power conversion efficiency of lead halide perovskite solar cells, the toxicity of lead and the unstable nature of the materials are still major concerns for their wider implementation at the industrial level. Herein, large-size single crystals (SCs) are developed in HI solution by using a temperature lowering method and nanocrystals (NCs) of A₃Bi₂I₉ perovskites [where A=CH₃NH₃⁺ (MA)⁺, Cs⁺, and (Rb_0.05Cs_2.95)⁺] are formed in ethanol (EtOH) and toluene (TOL). The stability of A₃Bi₂I₉ perovskite is investigated by immersing the SCs for 24 h and pellets for 12 h in water. Moreover, the A₃Bi₂I₉ perovskite NCs displays a promising photoluminescence quantum yield of 17.63 % and a long lifetime of 8.20 ns.     

Sky-Blue Triplet Emitters with Cyclometalated Imidazopyrazine-Based NHC-Ligands and Aromatic Bulky Acetylacetonates

Platinum(II) complexes with an N-heterocyclic carbene and a cyclometalating phenyl ligand (C^C*) are excellent candidates as efficient blue triplet emitters for OLED applications. The electronic and photophysical properties of these complexes can be fine-tuned with the objective to increase the quantum yields and lower the phosphorescence decay times. We found that platinum complexes with an imidazopyrazine C^C* ligand and bulky acetylacetonates are sky-blue triplet emitters, characterised by an almost unitary quantum yield and short phosphorescence decay times.     

Influence of electron beam pre-irradiation on the thermal behaviors of polyacrylonitrile

Thermal treatment of polyacrylonitrile pre-irradiated by electron beam was performed to investigate the radiation effects on thermally activated reactions. Thermal properties were characterized by differential scanning calorimetry and thermogravimetric analyses. Pre-irradiation lowers the onset temperature of reactions and alleviated the heat evolution process. Char yields (800 °C) of polyacrylonitrile increase significantly with increasing irradiation dose. FTIR was used to monitor the thermal reaction. The results reveal that the thermal reactions can be regulated by pre-irradiation dose. FTIR and UV-visible absorption spectra of pre-irradiation polyacrylonitrile illustrate the formation of -HCN-NCH- conjugation across the polymeric chains as a function of dose, which could improve the thermal behaviors of polyacrylonitrile.     

Fluorescence spectroscopy of potential electroluminescent materials: Substituent effects on DSB and segmented PPV derivatives

The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV) derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λ_a = 380–450 nm, ε = 20,000–60,000 M⁻¹ cm¹ and fluorescence maxima, quantum yields, and decay times of λ_r = 440–530 nm, Φ_f = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly the same absorption spectra, fluorescence spectra, and radiative rate constantsk _f= Φ_f/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φ_f and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep energy transfer processes between different oriented segments.     

Scintillation response of Ce-doped or intrinsic scintillating crystals in the range up to 1 MeV

A hybrid photomultiplier (HPMT) was used to study the scintillation response {N_phels(E) photoelectron and L.Y.(E) light yields and energy resolutions} of various known or newly developed scintillators—namely, Ce-doped crystals (perovskites or garnets), CsI(Tl) and the intrinsic BGO crystal—at different energies in the range 8 keV–1.33 MeV. Detailed comparative studies of the scintillation properties of these crystals are presented. A newly developed fast and heavy LuAG:Ce scintillator is characterized by about a 50% higher L.Y. compared to that of well-known and popular BGO (roughly 12 500 ph/MeV against 8080 ph/MeV, respectively).     

遥感植被指数和CASA模型估算山东省冬小麦单产

准确估算区域尺度冬小麦单产对明确区域农业生产现状与保证国家粮食安全有重要意义。光能利用率模型是作物单产估算的常用模型之一,模型中最大光能利用率（ξ_max）是准确估算作物单产的关键参数,作物的ξ_max是否随时间发生变化需要深入探讨。首先使用Savitzky-Golay（S-G）对中分辨率成像光谱仪（MODIS）时序植被指数数据进行滤波,采用差分法结合光谱突变法提取了山东省2000年-2015年冬小麦种植面积,并使用市级尺度年鉴统计面积对提取面积进行验证,然后使用固定ξ_max和变化ξ_max分别驱动光能利用率模型（CASA）,结合作物收获指数与冬小麦种植面积获取山东省2000年-2016年冬小麦单产时空分布特征,探讨最大光能利用率对作物单产模拟的影响。结果表明,滤波后的时序植被指数数据能够反映冬小麦生长的光谱特征,差分法与光谱突变法结合提取冬小麦面积具有较好的普适性,提取的多年冬小麦种植面积与年鉴统计冬小麦播种面积之间的决定系数（R2）达0.71;变化ξ_max情景下模拟的多年冬小麦单产与统计单产之间的决定系数更高,说明冬小麦ξ_max是随时间变化的,可能与冬小麦品种更替有关。基于统计与模拟的结果均显示山东省冬小麦单产在2000年-2016年间呈现增加趋势,两者表现出来的增加速率分别为93.12和149.79 kg·hm-2·a-1。在空间上,山东省冬小麦单产呈现西部高于东部的分布特征。     

Bifurcation for a functional yield chemostat when one competitor produces a toxin

A model, with general yield functions: Fi(S), i=1,2, of competition in the chemostat of two competitors for a single nutrient when one of the competitors produces toxin against its opponent is studied in this paper. The conditions in terms of the relevant parameters for the Hopf bifurcation of the three-dimensional system have been proved, which implies the existence of limit cycles in the 3-D system.     

Temperature dependence of the fluorescence quantum yields of diphenylsiloxane‐based copolymers in dilute solutions

The monomer and excimer fluorescence quantum yields of well‐defined poly(dimethylsiloxane‐co‐diphenylsiloxane)s with different diphenylsiloxane (Ph₂SiO) contents have been determined, along with those of 1,1,3,3‐tetraphenyl‐1,3‐dimethyldisiloxane and 1,1,3,3,5,5‐hexaphenyltrisiloxane‐1,5‐diol used as model compounds, in a dilute organic solvent at different temperatures. The measured fluorescence quantum yields of the copolymers are correlated with the fraction of the ? (CH₃)₂SiO? (Ph₂SiO)_n? (CH₃)₂SiO? structures. The monomer fluorescence yield for copolymers with low Ph₂SiO contents is dominated mainly by the isolated ? (CH₃)₂SiO? (Ph₂SiO)? (CH₃)₂SiO? unit, and the apparent mean binding energy of the excimer does not increase significantly with increasing Ph₂SiO content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 854–861, 2002