YAG:Er~(3+)激光晶体中Er~(3+)红外波段的荧光发射

YAG:Er~(3+)晶体中Er~(3+)在红外新波段所谓“大气窗口”的激光发射,由于具有优异性能,研究此材料者日益增多。但红外波段荧光光谱除有局部的报导外,尚无系统报导,近年来我们对0.80—3.00μm波段的Er~(3+)离子的荧光光谱,进行了较详细的研究,并获得了较为满意的结果。这些结果,对从事YAG:Er~(3+)材料和器件的工作者,无疑是较为有益的参考

激光晶体YAG:Er中的浓度效应

本文讨论了激光晶体YAG:Er中Er~(3+)浓度效应所引起的晶体结构畸变,Er~(3+)离子高激发态(~4S_(3/2),~4F_(9/2)和~2H_(11/2)能级)的发光与浓度猝灭,~4I_(11/2)→I_(13/2)自饱和跃迁和激光波长红移的变化规律。

Ho~(3+):Gd_3Ga_5O_(12)晶体的光谱性质及强度参数

本文详细地研究了Ho~(3+):Gd_3Ga_5O_(12)(以下简称Ho~(3+):GGG)中Ho~(3+)离子在0.5～3.0μm波段内的室温及77K温度下的荧光光谱。根据Judd—Ofelt理论,计算了Ho~(3+)离子的自发辐射电偶跃迁几率与辐射寿命等光谱强度参数。

Ho~(3+)离子及HoP_5O_(14)晶体的光谱性质

根据HoP_5O_(14)的吸收光谱和荧光光谱,用Judd-Ofelt理论计算了Ho~(3+)的强度参数.并计算了激发能级的辐射跃迁速率、辐射寿命、荧光分支比和积分发射截面等光谱参数.

激光晶体YAG中Er~(3+)的辐射跃迁

本文讨论和分析了激光晶体YAG中Er~(3+)离子的激光上能级的~4S_(3/2)、~4I_(11/2)和~4I_(13/2)辐射跃迁的有关因素。

(Nd,Ce):YAG晶体的激光性能

本文给出了(Nd,Ce) :YAG 晶体激光性能的实验结果。与优质 Nd:YAG 晶体比较,我们现在得到的双掺晶体的静态脉冲激光效率提高了80%,激光阈值也显著降低,并具有抗紫外特性。双掺晶体激光性能的大幅度提高,说明在 YAG 晶体里 Ce~(3+)是 Nd~(3+)很好的敏化离子。

基于4kW YAG激光器的激光拼焊焊接工艺

分析了激光拼焊工艺特征，重点研究了在大功率固体激光器条件下，激光拼焊焊接工艺中激光功率、焊接速度和离焦量等因素变化对焊接质量的影响，得出了变化规律曲线。并系统全面地研究了目前汽车常用板材全厚度系列激光拼焊工艺，采用叠代寻优的方法获得到了适用于全自动激光拼焊生产线的优化工艺规范。

Perovskite-type B-site Bi-doped ceramic membranes for oxygen separation

Novel mixed conducting oxides, B-site Bi-doped perovskites were exploited and synthesized. Cubic perovskite structures were formed for BaBi0.2COyFe0.8-yO3-delta (y less than or equal to 0.4) and BaBixCo0.2Fe0.8-xP3-delta (x=0.1-0.5) The materials exhibited considerable high oxygen permeability at high temperature. The oxygen permeation flux of BaBi0.2Co0.35Fe0.45O3-delta membrane reached about 0.77 x 10(-6) mol/cm(2) s under an air/helium oxygen partial pressure gradient at 900 degrees C, which was much higher than that of other bismuth-contained mixed conducting membranes. The permeation fluxes of the materials increased with the increase of cobalt content, but no apparent simple relationship was found with the bismuth content. The materials also demonstrated excellent reversibility of oxygen adsorption and desorption. Stable time-related oxygen permeation fluxes were found for BaBi0.2CO0.35Fe0.45O3-delta and BaBi0.3Co0.2Fe0.5O3-delta a membranes at 875 degrees C.

Easy fabrication of dense ceramic membrane for oxygen separation

A combined EDTA-citrate complexing method was developed for the easy preparation of mixed oxygen-ionic and electronic conducting dense ceramic membrane for oxygen separation. The nea method takes the advantage of lower calcination temperature for phase formation. lower membrane sintering temperature and higher relative density over the standard ceramic method.

Investigation of ideal zirconium-doped perovskite-type ceramic membrane materials for oxygen separation

Zirconium-doped perovskite-type membrane materials of BaCo0.4Fe0.6-xZrxO3-delta (x = 0-0.4) with mixed oxygen ion and electron conductivity were synthesized through a method of combining citric and EDTA acid complexes. The results of X-ray diffraction (XRD), oxygen temperature-programmed desorption (O-2-TPD) and hydrogen temperature-programmed reduction (H-2-TPR) showed that the incorporation of proper amount of zirconium into BaCo0.4Fe0.6O3-delta could stabilize the ideal and cubic structure of perovskite. Studies on the oxygen permeability of the as-synthesized membrane disks under air/He gradient indicated that the content of zirconium in these materials had great effects on oxygen permeation flux, activation energy for oxygen permeation and operation stability. The high oxygen permeation flux of 0.90 ml cm(-2) min(-1) at 950degreesC, the single activation energy for oxygen permeation in the range of 600-950 degreesC and the long-term operation stability at a relatively lower operational temperature of 800 degreesC under air/He gradient were achieved for the BaCo0.4Fe0.4Zr0.2O3-delta material. Meanwhile, the effect of carbon dioxide on structural stability and oxygen permeability of this material was also studied in detail, which revealed that the reversible stability could be attained for it. (C) 2002 Elsevier Science B.V. All rights reserved.

Titanium-based perovskite-type mixed conducting ceramic membranes for oxygen permeation

A titanium-based perovskite-type oxide was synthesized by an improved method of combining EDTA acid and citric acid complexes. High structural stability, good sintering ability, and relatively high oxygen permeation flux were obtained simultaneously for disks synthesized from this ceramic oxide. (C) 2002 Elsevier Science B.V All rights reserved.

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C-2 selectivity up to 40-70% was achieved, albeit that conversion rate were low, typically 0.5-3.5% at 800-900 degreesC with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/gamma -Al2O3 with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH4 conversion, 93.0% CO selectivity and 10.45 ml/cm(2) min oxygen permeation flux were achieved under steady state at 850 degreesC. Methane conversion and oxygen permeation flux increased with increasing temperature, No fracture of the membrane reactor was observed during syngas production. However, H-2-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875 degreesC for more than 500h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm(2) min. (C) 2001 Elsevier Science B.V. All rights reserved.