Measurement of integrated luminosities at BESIII for data samples at center-of-mass energies between 4.0 and 4.6 GeV

The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.     

Effect of external electric field on the terahertz transmission characteristics of electrolyte solutions

We fabricated a microfluidic chip with simple structure and good sealing performance, and studied the influence of the electric field on THz absorption intensity of liquid samples treated at different times by using THz time domain spectroscopy system. The tested liquids were deionised water and CuSO₄, CuCl₂, NaHCO₃, Na₂CO₃ and NaCl solutions. The transmission intensity of the THz wave increases as the standing time of the electrolyte solution in the electric field increases. The applied electric field alters the dipole moment of water molecules in the electrolyte solution, which affects the vibration and rotation of the whole water molecules, breaks the hydrogen bonds in the water, increases the number of single water molecules and leads to the enhancement of the THz transmission spectrum.     

强度解调型光纤光栅温度传感实验

光纤光栅在工程上应用广泛,但由于存在解调系统复杂、成本高,尤其是需要使用光纤光谱仪等波长解调仪器,使得光纤光栅很难走入本科教学的实验课堂.本文提出了一种基于窄线宽DFB激光器的强度解调方案,极大地简化了光纤光栅传感器的解调系统,完全满足较高分辨率和实时检测的系统要求.合理安排的温度传感实验可以非常直观地展示光纤光栅的线性传感性能,使得工程化的光纤光栅传感技术轻松走进本科教学课堂,具有极高的推广和应用潜力.     

基于连续量子级联激光器的1103.4cm–1处NH3混叠吸收光谱特性研究

由于NH3在大气气溶胶化学中具有重要作用,所以快速和精确反演NH3浓度对环境问题非常重要.本文以9.05μm的室温连续量子级联激光器(quantum cascade laser,QCL)作为光源,采用波长扫描直接吸收可调谐二极管激光吸收光谱(tunable diode laser absorption spectroscopy,TDLAS)技术,研究了QCL在1103.4 cm–1的光谱特性,获得了激光器控制的温度电流与波长的关系.设计了QCL二级温控的低压实验平台,测量氨气在1103.4 cm–1处的6条混叠吸收线,在降低压强的情况下谱线展宽变小,使混叠光谱分离,由此计算各条吸收线的线强,进一步对测量不确定度进行分析.针对混叠严重的光谱提出了低压分离单光谱精确反演气体浓度的方法,并进行了实验验证.通过与HITRAN数据库进行结果对比,得出氨气在1103.4 cm–1的实验测量线强值与数据库偏差为2.71%-4.71%,实验测量线强值的不确定度在2.42%-8.92%,极低压条件下反演浓度与实际值的偏差在1%-3%.     

Improved photoelectrochemical hydrogen production over decorated titania with copper and nickel oxides by optimizing the photoanode and reaction characteristics

We optimized photocatalytic hydrogen production over TiO₂-based photocatalyst by varying the dopant (nickel and copper oxide), thin film active area, nature and concentration of sacrificial agents, and light intensity in a photoelectrochemical (PEC) cell/dye-sensitized solar cell (DSSC). Various characterization techniques have been used to investigate the structural, morphological, optical, and PEC behavior of single and codoped TiO₂. The TiO₂ decorated with both Cu and Ni oxides with active area of 1 cm² in a mixture of 5 vol % glycerol and 1 M KOH under light intensity of 100 mWcm^?2 produced the maximum hydrogen of 338.4 μmol cm^?2 for 2 h. The superior photocatalyst performance of this photocatalyst is attributed to its small crystallite size and large pore size, as confirmed by X-ray diffractometer, Transmission electron microscopy (TEM), and surface area of Brunauer-Emmet-Teller (S_BET). The absorption edges of this photocatalyst had the highest red shift compared with single doped and pure TiO₂ because of more indirect transitions of the photoexcited electrons, greater charge carrier separation, and lower recombination rate. The photoanode active area of 1 cm² with better photocatalytic performance correlated with the number of defects and grain boundaries. Glycerol shifted the conduction band of the photocatalyst to more negative flat potential compared with others. Increasing the concentration of glycerol further than 5 vol% saturated the photocatalyst active sites, increased photooxidation intermediates of glycerol, and reduced the hydrogen production. The light intensity had the maximum impact on the hydrogen production and could strongly control the number of charge carriers in both the PEC cell and the DSSC.     

六方相LaOF∶Er,Yb的上转换发光及温度传感特性

氟氧化物兼有氧化物优异的稳定性和氟化物的低声子能量,是上转换发光材料的一种热点基质材料,因而研究六方相LaOF∶Er,Yb的上转换发光性能及其温度特性具有重要意义。本文采用水热法制备了六方相LaOF∶Er,Yb荧光材料,通过X射线衍射(XRD)、扫描电镜(SEM)和荧光光谱对其结构和上转换荧光性能进行表征。实验结果表明,水热法120℃得到六方相LaF3,经800℃和1000℃退火后分别形成四方相LaOF和六方相LaOF。980 nm激发下,六方相LaOF∶Er,Yb中Yb3+与Er3+存在能量传递,通过双光子吸收产生绿光和红光的上转换荧光,并且Yb3+与Er3+的最佳浓度分别为3%和1%。最后研究了六方相LaOF∶Er,Yb在温度传感方面的应用,其在150~400 K温度范围的相对灵敏度和绝对灵敏度分别为0.037 K-1和0.0043 K-1。该材料具有优异的温度传感特性,对荧光温度传感器件的设计和应用具有指导意义。     

基于混合表面等离子体弯曲波导的紧凑型宽带偏振分束转换器的设计研究

设计了一种宽带的基于混合表面等离子体弯曲波导的偏振分束转换器, 使用有限元法计算硅波导、混合表面等离子体波导的模场分布和有效折射率, 为器件建模仿真分析提供了依据. 使用时域有限差分法优化器件结构, 以获得最佳的性能参数. 由于混合表面等离子体波导的双折射增强, 设计获得的偏振分束转换器具有超小尺寸和宽带的工作特性. 仿真结果表明 在1550nm的中心波长处消光比大于23dB, 插入损耗小于0.8dB; 在80nm的带宽上, 横磁偏振光转换为横电偏振光的偏振转换效率大于95％.     

Characteristic material parameters of CIGS solar cell related with device performance

CIGS solar cells with power conversion efficiency (PCE) in the range of 1.82%–12.30% were obtained by using two-step process, and were further analyzed through various measurement techniques. Material parameters showed diverse values and some trends depending on the device performance. The lower performance device showed small integrated PL intensity, short minority life time, larger defect density and lower activation energy, whereas the higher performance device showed opposite values. We investigated relationship between material parameters and PCE of solar cells, and found that some physical parameters such as integrated PL intensity, minority life time, defect density, and difference between band gap and activation energy (E_g-E_a), which all reflect defect states in bulk and at pn interface, are strongly related with PCE and would be used as a good indicator to evaluate device performance quickly.