过氧化苯甲酰在液态聚碳硅烷交联中的应用

聚碳硅烷热解前的交联对于提高其最终陶瓷产率至关重要.研究了过氧化苯甲酰(BPO)引发液态超支化聚碳硅烷(HBPCS)的交联反应对于陶瓷产率的影响.FT-IR和GPC证实,添加为0.5%～2.0%(质量分数,下同)的BPO,即可在80～140℃下引发HBPCS交联;在考察的实验条件下,提高交联温度、延长反应时间或增加BPO用量,均可提高HBPCS交联程度.BPO用量为2.0%时,HBPCS交联样品在1000℃下的陶瓷产率高达65%,比未加BPO的提高25%.     

溶剂浸提法调节聚碳硅烷分子量及其分布的研究

真空热处理法去除聚碳硅烷(poIycarbosi-lane,PCS)小分子时,因伴随着化学反应导致PCS结构变化而降低其纺丝性能.溶剂浸提法则无此之虞.研究结果表明,不同溶剂对PCS的溶解能力是不同的,依次为:甲醇<二甲基甲酰胺<乙二醇单甲醚<无水乙醇<乙二醇单乙醚<异丙醇<甲酸乙酯<乙酸甲酯<正丙醇.这一溶解能力体现为可溶PCS量的不同和可溶PCS分子量的不同两个方面.溶解能力较大的溶剂可以溶解分子量较大的PCS;溶解量也较多.由于溶剂的这一特性,溶剂浸提法不仅可以用来去除小分子的PCS,而且可以用来调节PCS的分子量及其分布,改善其纺丝性能,提高其原丝强度,而不改变PCS的分子结构.     

Optical spectra of Eu2+ ion doped KMgF3 single crystals grown by Bridgman method

High-quality KMgF3 single crystal containing 0.5 mol% europium (Eu) was prepared by an improved Bridgman method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime were measured. The results indicate the reduction of Eu3+ to Eu2+ in the KMgF3 single crystal. Under the excitation of 259 nm, 370 nm and 394 nm, the sample has two distinct emissions of Eu2+:4f7→4f7(~363 nm) and 4f65d1→4f7 (~440 nm). The substitution site for Eu ion is confirmed. The optical property investigation result shows that the Eu2+ doped KMgF3 single crystal may be used as potential laser media and related materials for optical devices.     

刚性棒状金属有机聚合物

综述了在主链上含有过渡金属和刚性共轭有机桥的聚合物,即所谓的刚性棒状金属有机聚合物的种类、制备、性质及应用。     

Preparation and characterization of Y3Al5O12:Ln（Ln=Eu,Ce） phosphor powders by ultrasonic atomization and co-precipitation process

A novel technique for YAG:Ln(Ln=Eu,Ce) phosphor powder synthesis with a nanocrystalline structure was developed.Nanocrystalline YAG:Ln powder was prepared by an ultrasonic atomization and co-precipitation method using a mixture solution of ammonium hydroxide(NH3·H2O) and ammonium hydrogen carbonate(NH4HCO3) as precipitant.The as-prepared nano-powders were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),and fluorescence spectrometer.The obtained phosphor powders were homogenous and in size of 50-70 nm.The results demonstrated that by using ultrasonic atomization and co-precipitation process,we could synthesize a good quality YAG:Ln(Ln=Eu,Ce) phosphor powder that had many potential applications.     

低氧含量液态超支化聚碳硅烷的合成与陶瓷化研究

以甲醇对氯甲基三氯硅烷(Cl3SiCH2Cl)进行烷氧化反应,然后经过格氏偶联反应和还原反应,制备了低氧含量液态超支化聚碳硅烷(HBPCS)。通过凝胶渗透色谱法(GPC)、核磁共振(NMR)以及元素分析对由此制备的HBPCS进行表征。结果表明,提高烷氧化比例,可以有效抑制溶剂四氢呋喃开环的副反应,降低先驱体氧含量。通过热失重分析(TGA)和X射线衍射(XRD)分别对HBPCS的热性能及相应陶瓷在高温下的结晶行为进行研究。     

Bi/Tm共掺TiO2-BaO-SiO2-Ga2O3玻璃光谱特性与能量转换机理研究

用高温熔融法制备了Bi、Tm、Bi/Tm掺杂TiO₂-BaO-SiO₂-Ga₂O₃玻璃系统。在808 nm激光激发下, 与Tm单掺杂玻璃相比, Bi/Tm共掺玻璃中Tm³⁺的³H₄→³F₄跃迁荧光(~1485 nm)得到了显著的增强, 而Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)减弱。在980 nm激光激发下, Tm单掺玻璃中没有观察到Tm离子的特征发光, 而在Bi/Tm共掺玻璃中观察到Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)。这是由于在808和980 nm激光二极管(LD)各自激发下, Bi/Tm共掺玻璃中活性Bi离子的近红外发光能量传递给Tm³⁺, 分别产生³F₄→³H₄与³H₆→³H₅跃迁所致。采用Inokuti-Hirayama模型, 分析了该玻璃体系中Bi→Tm的能量传递机理。结果表明, Bi→Tm的能量传递属于电偶极–偶极相互作用。     

Gain properties of germanate glasses singly doped with Tm^3＋ and Ho^3＋ ions

Two kinds of germanate glasses singly doped with the ion concentration of 2.0mol.%Tm3+ and 2.0mol.%Ho3+, respectively, were prepared. According to McCumber theory, the absorption and stimulated emission cross-sections corresponding to the 3H6←→3F4 transitions of Tm3+ (at 1.8 μm) and the 5I8←→5I7 transitions of Ho3+ (at 2.0 μm) were obtained, and respective gain cross-section spectra were also computed as a function of population inversion according to absorption and emission cross-sections and the ion concentrations. For Tm3+-doped germanate glasses, the maximum of the absorption, emission, and gain cross-sections reached a value higher than those reported for fluorozirconate, fluoride, and oxyfluoride glasses. For Ho3+-doped germanate glasses, the maximum of absorption, emission, and gain cross-sections reached a value higher than that reported for fluorozircoaluminate glasses. Hence, these Tm3+-doped and Ho3+-doped germanate glasses exhibited an advantage for application in mid-infrared lasers at about 1.8 and 2.0 μm wavelength.     

氢型沸石掺杂聚乙烯醇膜的渗透蒸发性质及其在酯化反应中的催化作用研究

通过在PVA膜中掺杂沸石制得兼具催化和分离功能的酯化膜反应器。实验结果表明：在不同的沸石掺杂的乙酸／乙醇酯化体系中,氢型沸石不仅可以较大地提高PVA膜的渗透通量,其分离系统也较高,膜的适宜填充度应小于40％（质量比）,随填充度的增加,膜的催化活性和酯化转化率均有较大提高,酯化反应温度的升高,有利于反应速率及转化率的提高,对于乙酸／乙醇体系,最佳醇／酸＝1．2：1;不同的酯化体系,填充氢型涨均有利于其转化率的提高,但因体系而异。     

Enhanced emission of 2.9 μm from Ho3+/Pr3+ co-doped LiYF4 crystal excited by 640 nm

The use of Pr3+co-doping for great enhancement of mid-infrared(mid-IR) emissions at 2.9 μm and 2.4 μm is investigated in the Ho3+/Pr3+co-doped LiYF4 crystals.With the introduction of Pr3+ions,the fluorescence lifetime of Ho3+:5I7 level is 2.15 ms for Ho3+/Pr3+co-doped crystal,and the lifetime for Ho3+singly doped crystal is 17.70 ms,while the lifetime of Ho3+:5I6 level decreases slightly from 2.11 ms for Ho3+:LiYF4 to 1.83 ms for Ho3+/Pr3+:LiYF4.It is also demonstrated that the introduction of Pr3+greatly increases the mid-infrared emission of Ho3+:5I6 →5I7 which depopulates the Ho3+:5I7 level,while it has little influence on the Ho3+:5I6 level,which is beneficial for greater population inversion and laser operation.The analysis on the decay curves of the 2.0 μm emissions in the framework of the Inokuti-Hirayama model indicates that the energy transfer from Ho3+to Pr3+is mainly from electric dipole-dipole interaction.The calculated efficiency of energy transfer from Ho3+:5I7 to Pr3+:3F2 level is 87.53% for Ho3+/Pr3+(1.02%/0.22%) co-doped sample.Our results suggest that the Ho3+/Pr3+co-doped LiYF4 single crystals may have potential applications in mid-IR lasers.