Synthesis of carbon dots with a tunable photoluminescence and their applications for the detection of acetone and hydrogen peroxide

Carbon dots(CDs) with multi-color emissive properties and a high photoluminescent quantum yield(PLQY) have attracted great attention recently due to their potential applications in chemical,environmental,biological and photo-electronic fields.Solvent-dependent effect in photoluminescence provides a facial and effective approach to tune the emission of CDs.In this study,green emissive nitrogen-doped carbon dots(N-CDs) are synthesized from p-hydroquinone and ethylenediamine through a simple hydrothermal method.The as-prepared N-CDs possess a robust excitation-independent green luminescence and a high PLQY of up to 15.9%.Further spectroscopic characterization indicates that the high PLQY is achieved by the balance of nitrogen doping states and the surface passivation extent in CDs.The N-CDs also exhibit solvent-dependent multi-color emissive property and distinct PLQY in different solvents(the maximum can reach up to 25.3%).Furthermore,the as-prepared N-CDs are applied as fluorescence probes to detect acetone and H2O2 in water.This method has exhibited a low detection limit of acetone(less than 0.1 %) and a quick and linear response to the H_2O_2 with the concentration from 0 to 120 μmol/L.This work broadens the knowledge of applying CDs as probes in the bio and chemical sensing fields.     

Ablation yield and angular distribution of ablated particles from laser-irradiated metals: The most fundamental determining factor

Five metals (Zn, Cu, Ni, Ti, and Mo) were irradiated with 150 shots of a Q-switched Nd:YAG pulsed laser in a vacuum of 10⁻³ torr. The ions projected out of the laser-produced plasma (LPP) plume were detected by CR-39 detectors positioned at −15°, 0°, 30°, 60°, and 90° with respect to the target-surface normal at a distance of 5 cm from the target in each case. The angular distribution of LPP ions, which is characterized by the exponent n of cosⁿ θ distribution, is given by n = 2.5-11 for the five target metals. The value of the exponent n has no systematic correlation with the square-root of atomic mass of the target metals but exhibits systematic dependence on the room temperature Debye-Waller's thermal parameter B or the mean-square amplitude of atomic vibrations 〈u²〉. Likewise, the ablation yield (atoms/shot) of the twelve target metals investigated by Thestrup et al. (2002) [8] under identical irradiation conditions is a function of the room temperature B-factor or 〈u²〉.     

A new probe of neutron skin thickness

The correlation between neutron-to-proton yield ratio (R_np) and neutron skin thickness (δ_np) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding R_np is obtained. The results show strong linear correlation between R_np and δ_np for neutron-rich Ca and Ni isotopes. It is suggested that R_np may be used as an experimental observable to extract δ_np for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state (EOS) of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.     

Influence of Gd doping on the absolute quantum efficiency and lifetime of EuxGd1-x（TTA）3phens

Absolute quantum yield （Ф） is one of the most important parameters to evaluate the potential of novel materials. Lanthanide complexes EuxGd1-x（TTA）3phens are synthesized with the ratio of Gd3＋ dopant concentration ranging from 10% to 90% to improve the absolute quantum yield. EuxGd1-x（TTA）3phens possess similar infrared and ultraviolet spectra, showing that they have similar molecular structures. The absolute emission quantum yields of EuxGd1-x（TTA）3phens are determined using a fluoromax-4 spectrofluorometer equipped with an integrating sphere. The fluorescence lifetimes of the EuxGd1-x（TTA）3phens are measured in the same experiment. It was found that both absolute quantum yields and fluorescence lifetimes of EuxGd1-x（TTA）3phens are of quasi-periodic variation with the change of the Gd3. dopant concentrations. The absolute quantum efficiency and fluorescence lifetime vary with respect to the Gd content in an opposite fashion, indicating that the rate of energy absorption by the EuxGd1-x（TTA）3phens and the conversion to light energy is critical for the absolute quantum efficiency. The radiative rate constant Kr and non-radiative rate constant Knr are calculated. The dependence of Kr and Knr on the Gd3＋ dopant concentrations is very similar to that of absolute quantum efficiency. The radiation rate constant Kr and absolute quantum efficiency have a linear relationship.     

Nanosized starlike molecules. Synthesis and optical properties of tris- and tetrakis[oligo(disilanylenebithienylene)dimethylsilyl]benzene

The syntheses of two types of starlike molecules with the arms that extend to three and four directions have been reported. The molecules with the arms consisting of a regular alternating arrangement of a silicon-silicon bond and bithienylene unit that extend to three directions were synthesized by the reactions of 1,3,5-tris(chlorodimethylsilyl)benzene, which was chosen as a core, with the lithio[oligo(disilanylenebithienylene)] derivatives. The starlike molecules with extended arms to four directions were prepared by the reaction of 1,2,4,5-tetrakis(fluorodimethylsilyl)benzene used as a core, with lithio[oligo(disilanylenebithienylene)]s. UV-Vis absorption and fluorescence properties of these starlike molecules have been investigated in a dioxane solution. The present molecules showed absorption maxima in a range of 321-337 nm, and revealed higher fluorescence quantum yields than that of the corresponding linear polymer, poly[(tetraethyldisilanylene)bithiophene].     

Synthesis of highly fluorescent LaF3:Ln/LaF3 core/shell nanocrystals by a surfactant-free aqueous solution route

A surfactant-free aqueous solution route has been established for the synthesis of LaF₃:Ln³⁺/LaF₃ core/shell nanocrystals (Ln=Ce, Tb, Nd) heated at 75 °C at ambient pressure. All the as-prepared nanocrystals with spherical shape have an average size around 20 nm, and consist of well crystallized hexagonal phases. The X-ray photoelectron spectra was used to confirm that the LaF₃ shells have coated the LaF₃:Ce³⁺, Tb³⁺ cores. Compared with that of the original cores under the same conditions, the emission intensity of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ and LaF₃:Nd³⁺/LaF₃ core/shell nanocrystals increased significantly of 120% and 60%, respectively. The quantum yield of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ core/shell nanocrystals reached about 27% in aqueous solution. These results indicate that a significant reduction of the quenching from the surface of the core nanocrystals can be obtained by the synthesis of the core/shell structures, and this method can provide more desirable lanthanide-doped nanocrystals for potential biological applications.     

再制造中零件供应系统整合优化研究

再制造企业里,在决策购买新零件或修复旧零件时,经常面对有限的拆卸修复信息和不确定的订货提前期.为了得到科学的决策,人们试图尽早地掌握拆卸修复零件的确切信息,与有能力的供应商建立良好的关系,或在企业建立管理信息系统来统计分析废旧品的状态和数量等.根据市场需求和产品批发价,以满足市场需求所要购买新零件数和拆卸修复机器数为决策变量,并考虑拆卸修复成功的概率,建立企业期望利润的数学模型,求得可能情况下的最优解或现实满意解.洞察再制造企业取得最大利润的主要影响因数及这些因数间的关系,为制作生产计划提供理论依据.最后指出进一步的研究问题.     

含吡啶环的芳香醚-噁二唑类化合物的合成及其光谱研究

为开发新的高强度的有机电致发光材料, 用含烷氧基的取代苯甲酸(2)与2,6-吡啶二甲酰肼(3)在POCl3作用下, “一锅煮”法合成6个结构对称的含吡啶环的芳香醚-噁二唑4a～4f. 通过MS, IR, 1H NMR, 元素分析等手段对其结构进行了表征. 化合物的荧光性能测定结果显示此类化合物具有良好的荧光性, 其荧光发射波长均在347～507 nm范围内, 最大荧光发射波长在384 nm附近处, 且荧光强度较强. 在芳环上引入5-Br基团(4e, 4f), 化合物的荧光发射波长发生红移, 荧光强度有所减弱. 以硫酸奎宁作参比, 测定6个目标产物的荧光量子产率, 5-Br基团的引入对荧光量子产率没有明显影响. 同时讨论了代表性产物4a在不同溶剂中最大荧光激发波长处的荧光量子产率, 发现溶剂极性对该类化合物的荧光量子产率基本没有影响.     

Analysis of a chemostat model with variable yield coefficient: Tessier kinetics

We investigate a chemostat model in which the growth rate is given by a Tessier expression with a variable yield coefficient. We combine analytical results with path-following methods. The washout conditions are found. When washout does not occur we establish the conditions under which the reactor performance and reactor productivity are maximised. We also determine the parameter region in which oscillations may be generated in the reactor. We briefly discuss the implications of our results for comparing the performance of a single bioreactor against a cascade of two bioreactors.     

一种蓝光单体的合成及其荧光性能研究

吡唑啉衍生物在生物医药[1,2]应用的领域非常广泛.吡唑啉还是一种优质的发光材料[3],其发射波长位于450nm左右,具有很高的荧光量子效率,且发光波长窄,色纯度好,是一种纯正的蓝光.当吡唑啉环3位引入给电子基时,化合物则具有很高的荧光量子产率,可制得具有高热稳定性的空穴传输蓝光发光材料[4-6]和荧光探针[7].它还可以将吸收的不可见的紫外光转变为蓝色的可见光反射出来,从而增加了光线的反射率,使被其处理过的物体白度和光泽提高,所以吡唑啉又被做为荧光增白剂和荧光染料[8,9]进行广泛地应用.