3D Micromolding of Arrayed Waveguide Gratings on Upconversion Luminescent Layers for Flexible Transparent Displays without Mirrors,Electrodes, and Electric Circuits

A new technique for the fabrication of arrayed waveguide gratings on upconversion luminescent layers for flexible transparent displays is reported. Ho³⁺‐ and Yb³⁺‐codoped NaYF₄ nanoparticles are synthesized by hydrothermal techniques. Transparent films consisting of two transparent polymers on the NaYF₄ nanoparticle films exhibit mechanical flexibility and high transparence in visible region. Patterned NaYF₄ nanoparticle films are fabricated by calcination‐free micromolding in capillaries. Arrayed waveguide gratings consisting of the two transparent polymers are formed on the patterned NaYF₄ nanoparticle films by micromolding in capillaries. Green and red luminescence is observed from the upconversion luminescent layers of the NaYF₄ nanoparticle films in the arrayed waveguide gratings under excitation at 980 nm laser light. Arrayed waveguide gratings on the upconversion luminescent layers are fabricated with Er³⁺‐doped NaYF₄ nanoparticles which can convert two photons at 850 and 1500 nm into single photon at 550 nm. These results demonstrate that flexible transparent displays can be fabricated by constructing arrayed waveguide gratings on upconversion luminescent layers, which can operate in nonprojection mode without mirrors, transparent electrodes, and electric circuits.     

The Role of Higher Lying Electronic States in Charge Photogeneration in Organic Solar Cells

The role of excess photon energy on charge generation efficiency in bulk heterojunction solar cells is still an open issue for the organic photovoltaic community. Here, the spectral dependence of the internal quantum efficiency (IQE) for a poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b]­dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)]:6,6‐phenyl‐C₆₁‐butyric acid methyl ester (PCPDTBT:PC60BM)‐based solar cell is derived combining accurate optoelectronic characterization and comprehensive optical modeling. This joint approach is shown to be essential to get reliable values of the IQE. Photons with energy higher than the bandgap of the donor material can effectively contribute to enhance the IQE of the solar cell. This holds true independently of the device architecture, reflecting an intrinsic property of the active material. Moreover, the nanomorphology of the bulk heterojunction plays a crucial role in determining the IQE spectral dependence: the coarser and more crystalline, the lesser the gain in IQE upon high energy excitation.     

塑料闪烁体的闪烁时间特性

采用137Cs激发塑料闪烁体发光,应用单光子计数法测量塑料闪烁体发光衰减曲线。根据测量原理搭建了实验平台,测量了ST401和EJ232两种闪烁体的闪烁时间特性。实验结果用双指数拟合法进行分析可得,ST401发光衰减常数为2.9 ns和50 ns,EJ232发光衰减常数为1.6 ns和30 ns。实验平台所测幅度动态范围大于104,时间分辨小于0.8 ns。从统计学分析单光子计数法的物理过程,并采用蒙特卡罗方法模拟整个探测过程,探讨单光子计数法的适用条件。实验结果与数值模拟结果相洽。若终止探测器平均探测到的光子数不大于0.1,则多道测量结果可以近似为塑料闪烁体发光衰减曲线。     

高分辨SPI/TOFMS的研制及VOCs分子式确定

单光子能量10.6eV的真空紫外灯可电离大部分的挥发性有机物,生成分子离子,几乎无碎片,谱图简单。本文介绍了实验室自制的真空紫外灯单光子电离反射式飞行时间质谱仪的原理、仪器结构及初步结果。测试仪器分辨率超过4000(FWHM),质量精度优于6ppm。苯的检出限可至52ppbv。将仪器用于香烟烟气和聚氯乙烯(PVC)热解产物的检测。结果表明,单光子软电离源与高分辨质谱的结合,可直接用于复杂挥发性有机物(VOCs)分子式的确定。     

SPECT reconstruction with sub‐sinogram acquisitions

Described herein are the advantages of using sub‐sinograms for single photon emission computed tomography image reconstruction. A sub‐sinogram is a sinogram acquired with an entire data acquisition protocol, but in a fraction of the total acquisition time. A total‐sinogram is the summation of all sub‐sinograms. Images can be reconstructed from the total‐sinogram or from sub‐sinograms and then be summed to produce the final image. For a linear reconstruction method such as the filtered backprojection algorithm, there is no advantage of using sub‐sinograms. However, for nonlinear methods such as the maximum likelihood (ML) expectation maximization algorithm, the use of sub‐sinograms can produce better results. The ML estimator is a random variable, and one ML reconstruction is one realization of the random variable. The ML solution is better obtained via the mean value of the random variable of the ML estimator. Sub‐sinograms can provide many realizations of the ML estimator. We show that the use of sub‐sinograms can produce better estimations for the ML solution than can the total‐sinogram and can also reduce the statistical noise within iteratively reconstructed images. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 247–252, 2011;     

Efficient flexible phosphorescent polymer light-emitting diodes based on silver nanowire-polymer composite electrode

Blue, green, and red electrophosphorescent polymer light-emitting diodes have been fabricated on silver nanowire-polymer composite electrode. The devices are 20%-50% more efficient than control devices on ITO/glass and exhibit small efficiency roll-off at high luminances. The blue PLEDs were repeatedly bent to 1.5 mm radius concave or convex with calculated strain in the emissive layer approximately 5% (tensile or compressive).