下转换材料β-NaYF4:Tb3+,Yb3+的水热法合成和发光性质研究

利用水热法合成了粉末发光材NaYF4∶Tb3+,Yb3+。分别用X射线衍射(XRD),光致发光谱(PL)和激发谱(PLE)测试了合成材料的物相结构和发光性质。研究结果表明:合成的NaYF4∶Tb3+,Yb3+材料为六方相的晶体,无立方相的。改变Tb3+和Yb3+的掺杂浓度后晶格结构没有变化,说明离子Tb3+和Yb3+取代的是Y3+离子的晶格位置。在355nm脉冲激光激发下,检测到了Tb3+的5 D3→7 FJ(J=5-0)和5 D4→7 FJ(J=6,5,4,3)可见波段特征发射光和Yb3+950～1 050nm(2 F5/2→2 F7/2)的近红外发光,研究了可见和近红外的发射强度随Yb3+掺杂浓度的变化,表明Tb3+和Yb3+之间存在能量传递,其可能的能量传递方式是共合作能量传递过程。当Tb3+和Yb3+的掺杂摩尔浓度分别是1mol%和6mol%时具有最强的近红外发射。     

手性联萘桥联双卟啉的电子光谱与二阶非线性光学性质

在6-31G(d,p)水平上用B3LYP方法对手性联萘桥联双卟啉系列分子进行几何构型优化. 用半经验ZINDO/S方法计算了这些分子的电子光谱, 结果表明手性联萘桥联双卟啉中两个卟啉生色团之间存在强的激子耦合作用, B带的Davydov分裂大小与两个卟啉环的相对取向以及卟啉环中心之间距离有关. 用ZINDO/SOS方法计算了分子的一阶超极化率. 卟啉环上引入推/拉电子基团可以有效地提高手性联萘桥联双卟啉的二阶非线性光学系数. 一阶超极化率的大小与双卟啉中推/拉电子基团的空间排列方式有关. 一阶超极化率的提高不仅与分子激发态与基态偶极矩差增大有关, 还和基态偶极矩与激子耦合激发态跃迁矩矢量的相对取向密切相关.     

Generation and expansion of laser-induced plasma as a spectroscopic emission source

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy (LIBS) has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermodynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.     

谈谈弹塑性力学中的简化问题

讨论了弹塑性力学中的基本假设、本构模型和简化分析方法. 指出在这一领域中, 简化是非常重要的和必需的.