Dependence of photoluminescence of CdSe/ZnS on excitation wavelength

We have found that the photoluminescence (PL) intensity of CdSe/ZnS nanocrystals placed on a thin film of insulator (GaAsOx/GaAs) depends on excitation wavelength through the interference effects of the excitation light. By employing the multi-reflection/interference calculation, the insulator thickness of the underlying non-uniform patterns can be evaluated by the simple observation of CdSe/ZnS PL with a couple of excitation wavelengths. Moreover, the differences observed for the temporal evolution of CdSe/ZnS PL (blue shifts and degradation) among the excitation wavelengths suggest that the photo-induced changes of chemical composition and surface ligands are responsible for blue shifts and degradation, respectively.     

低气压微波感耦氩等离子体空间分布特性光谱诊断

用二维光学多道分析仪研究了低气压表面波型微波感耦氬等离子体的光谱辐射特性?鼳bel反演后,得到了在各种气压和微波功率下等离子体辐射光强和激发温度的空间分布及其变化规律。讨论了此等离子体的激发机理。     

盐/甲醇体系荧光光谱的分析和指认

研究了CaCl2、LiCl和Ca(NO3)2在甲醇溶液中的荧光光谱,并对溶液中可能的团簇构型采用密度泛函理论和含时(TD)密度泛函理论中的B3LYP方法进行结构优化和激发能计算.实验结果表明CaCl2和LiCl与甲醇形成了具有荧光性质的簇合物,且随着CaCl2和LiCl浓度的增加溶液的荧光强度整体呈增强趋势,而Ca(NO3)2与甲醇相互作用使甲醇发生荧光猝灭.理论计算得到盐/甲醇溶液中可能存在多种簇合物,但能使甲醇溶液荧光增强的团簇构型主要为[CaCl(CH3OH)n]+和LiCl(CH3OH)n,而NO3-与甲醇通过氢键作用形成簇合物的振荡强度几乎为零,解释了NO3-使甲醇发生荧光猝灭的现象.     

Characterization of aquatic dissolved organic matter by asymmetrical flow field-flow fractionation coupled to UV-Visible diode array and excitation emission matrix fluorescence

Flow field-flow fractionation (FlFFF) with on-line UV/Visible diode array detector (DAD) and excitation emission matrix (EEM) fluorescence detector has been developed for the characterization of optical properties of aquatic dissolved organic matter (DOM) collected in the Otonabee River (Ontario, Canada) and Athabasca River (Alberta, Canada). The molecular weight (MW) distribution of DOM was estimated using a series of organic macromolecules ranging from 479 to 66,000 Da. Both the number-average (M_n) and weight-average (M_w) molecular weights of Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA) determined using these macromolecular standards were comparable to those obtained using polystyrenesulfonate (PSS) standards, suggesting that organic macromolecules can be used to estimate MW of natural organic colloids. The MW of eight river DOM samples determined by this method was found to have an M_n range of 0.8–1.1 kDa, which agrees with available literature estimates. The FlFFF-DAD-EEM system provided insight into the MW components of river DOM including the optical properties by on-line absorbance and fluorescence measurement. A red-shift in emission and excitation wavelength maxima associated with lower spectral slope ratios (S_R = S_275–295:S_350–400) was related to higher MW DOM. However, DOM of different origins at similar MW also showed significant difference in optical properties. A difference of 47 and 40 nm in excitation and emission peak C maxima was found. This supports the hypothesis that river DOM is not uniform in size and optical composition.     

隐性字迹的快速光谱显现与高光谱分类技术研究

擦除、密写、掩盖等隐性字迹的快速、无损显现与检验是法庭科学文件检验领域的研究难点。当前多采用切换多波段光源与滤光片的方法对隐性字迹进行显现,但对隐性字迹显现的光谱学机理分析较少,因此隐性字迹的显现效率与检验成功率均不高。为提高擦除、密写、掩盖三类隐性字迹的显现效率与检验精度,通过测量字迹的激发与荧光光谱、反射与透过光谱、微观形貌,对其显现机理与快速显现方法进行深入研究。并且基于液晶可调谐滤光器（LCTF）的高光谱成像技术与支持向量机（SVM）分类算法,提出一种对隐性字迹同时显现与分类的快速检验方法。晨光与百乐可擦笔字、荧光密写笔、柠檬汁均可在365 nm长波紫外光激发下发出较强荧光,其中可擦笔和柠檬汁的荧光波长为716 nm左右,荧光密写笔荧光波长为447 nm。此外,采用254或365 nm波长对柠檬汁隐性字迹进行紫外反射成像也可有效显现柠檬汁字迹。掩盖字迹的研究中发现,在700～2 500 nm红外波段,走珠笔、记号笔、可擦笔字迹透过率在60%以上,而中性笔字迹透过率在20%以下。因此,采用近红外波段850 nm成像有效显现了百乐走珠笔所覆盖的晨光中性笔字迹。同时,采用LCTF高光谱相机对三类隐性字迹在400～720 nm范围进行步长为5 nm的高光谱成像,并通过SVM分类算法对图像中不同笔迹成分进行同时显现和分类,分类总精度达99.284 4%,Kappa系数达0.959 1。以365 nm波长光源作为激发光进行光致发光成像可有效显现擦除与密写字迹。由于不同墨迹在近红外波段反射率差异较大,近红外成像可以有效显现掩盖字迹。基于LCTF高光谱成像的SVM分类技术可实现不同类别隐性字迹的同时显现与分类,并且有较高的显现效率与分类精度。     

甲醇分子(CH3OH)光谱性质的理论计算

研究了气相甲醇分子(CH3OH)基态和激发态性质。在对不同方法基组所得计算结果和实验结果进行比较之后,选用MP2(full)/6-311++G(2d,2p)理论方法进行计算,得到甲醇分子(CH3OH)基态和三重激发态的几何结构、能量以及频率信息;频率计算显示基态和三重态都为稳定构型。从三重态的结构出发,解释了三重态势能面为排斥型势能面的合理性。计算了甲醇分子单重激发态的垂直激发能,比较不同方法不同基组计算的甲醇分子单重激发态的垂直激发能,发现用TDDFT 中的b3p86方法使用6-311++G**基组的计算值和实验值符合得最好。计算得到的甲醇分子在MP2(full)/6-311++G(2d,2p)的绝热电离能和垂直电离能分别为11.18eV和11.32eV;计算得到的绝热电子亲和势与垂直电子亲和势分别为0.888eV和0.893eV。计算结果对实验研究有指导意义。     

1.54 μm Light emission from Er/O and Er/F doped Si p–i–n diodes grown by molecular beam epitaxy

Various light emitting devices (LED) have been processed using Er/O- and Er/F-doped Si layered structures grown by molecular beam epitaxy (MBE) at low temperature. A comparative study has been carried out in order to provide more understanding of the electroluminescence (EL) excitation and de-excitation mechanisms in particular at a high injection current regime. Comparing the experimental results with model calculations the values of excitation cross section, σ_ex, and effective Auger coefficient, C_A, have been determined for various devices operated at different biases. Time-resolved EL measurements of these Er/O- and Er/F-doped MBE Si structures, using an experimental set-up with a time response of 200 ns, have been performed with different excitation conditions. Besides the spontaneous Er emission (700 μs), some fast EL decay processes associated with the Auger energy transfer via free carriers (4 μs), and the hot carrier effects (200 ns) have been identified.     

A fast calculation of excitation autoionization cross-sections of Na-like ions

In this work, based on the calculation in detail, two new fitting formulae of total excitation and excitation autoionization cross-sections for Na-like ions (18?Z?39) are given. For discussing the variation of the total excitation autoionization cross-section, a systematic study of the dependence of the overall branching ratio on incident electron energy and nuclear charge is also carried out.     

Characteristics of Analyte Ionization in Low Power Microwave Plasma Torch

The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ionization were observed. The axial profiles of the degree of the ionization of some elements were determined. The experimental results are very important for developing the new analytical source——microwave plasma torch (MPT).