Spectroscopic properties of Ce : YAP scintillation crystal grown by temperature gradient technique

Spectroscopic properties of Ce-doped yttrium orthoaluminate (Ce:YAlO3 or Ce:YAP) crystals grown by temperature gradient technique (TGT) were investigated, and the effects of the growth conditions on the properties were analyzed.. Methods of optical absorption (OA), photoluminescence (PL), photoluminescence decay (PLD), X-ray excited luminescence (XL) and cathodeluminescence (CL) were used in these investigations. The results showed that the absorption band peak at 202, 394 and 532 nm originated from F and F+ color center induced by the weak reducing growth atmosphere, green emission band near 500 ran derived from Ce3+ -Ce3+ pairs and band at 650 similar to 850 run from some unintentional impurity in crystals.

Electrical properties and electroluminescence of 4H-SiC p-n junction diodes

Homoepitaxial growth of 4H-SiC on off-oriented Si-face(0001) substrates was performed by using the step-controlled epitaxy technique in a newly developed low-pressure hot-wall CVD (LP-HWCVD) system with a horizontal air-cooled quartz tube at around 1500 degreesC and 1.33 x 10(4) Pa by employing SiH4 + C2H4 + H-2. In-situ doping during growth was carried out by adding NH3 gas into the precursor gases. It was shown that the maximum Hall mobility of the undoped 4H-SiC epilayers at room temperature is about 430 cm(2) (.) V-1 (.) s(-1) with a carrier concentration of similar to 10(16) cm(-3) and the highest carrier concentration of the N-doped 4H-SiC epilayer obtained at NH3 flow rate of 3 sccm is about 2.7 x 10(21) cm(-3) with a mobility of 0.75 cm(2) (.) V-1 (.) s(-1). SiC p-n junctions were obtained by epitaxially growing N-doped 4H-SiC epilayers on Al-doped 4H-SiC substrates. The C - V characteristics of the diodes were linear in the 1/C-3 - V coordinates indicating that the obtained p-n junctions were graded with a built-in voltage of 2.7 eV. The room temperature electroluminescence spectra of 4H-SiC p-n junctions are studied as a function of forward current. The D-A pair recombination due to nitrogen donors and the unintentional, deep boron center is dominant at low forward bias, while the D-A pair recombination due to nitrogen donors and aluminum acceptors are dominant at higher forward biases. The p-n junctions could operate at temperature of up to 400 degreesC, which provides a potential for high-temperature applications.

Growth of ZnO single crystal by chemical vapor transport method

ZnO crystals were grown by CVT method in closed quartz tube under seeded condition. Carbon was used as a transport agent to enhance the chemical transport of ZnO in the growth process. ZnO single crystals were grown by using GaN/sapphire and GaN/Si wafer as seeds. The property and crystal quality of the ZnO single crystals was studied by photoluminescence spectroscopy and X-ray diffraction technique.

Growth and characterization of semi-insulating GaN films grown by MOCVD

High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arc-min, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 degrees C was measured to be approximate 10(9) and 10(6) Omega(.)cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.

Growth of high quality semi-insulating InP single crystal by suppression of compensation defects

Deep level defects in as-grown and annealed SI-InP samples were investigated by thermally stimulated current spectroscopy. Correlations between electrical property, compensation ratio, thermal stability and deep defect concentration in SI-InP were revealed. An optimized crystal growth condition for high quality SI-InP was demonstrated based on the experimental results.

Growth of ZnO single crystal by chemical vapor transport method

ZnO crystals were grown by CVT method in closed quartz tube under seeded condition. Carbon was used as a transport agent to enhance the chemical transport of ZnO in the growth process. ZnO single crystals were grown by using GaN/sapphire and GaN/Si wafer as seeds. The property and crystal quality of the ZnO single crystals was studied by photoluminescence spectroscopy and X-ray diffraction technique.

Growth and characterization of semi-insulating GaN films grown by MOCVD

High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arc-min, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 degrees C was measured to be approximate 10(9) and 10(6) Omega(.)cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.

Growth of high quality semi-insulating InP single crystal by suppression of compensation defects

Deep level defects in as-grown and annealed SI-InP samples were investigated by thermally stimulated current spectroscopy. Correlations between electrical property, compensation ratio, thermal stability and deep defect concentration in SI-InP were revealed. An optimized crystal growth condition for high quality SI-InP was demonstrated based on the experimental results.

Cyanex923萃取稀土热力学、动力学及界面现象的研究

本文研究了中性萃取剂三烷基氧化膦(Cyanex 923)从硫酸介质中萃取与反萃三价稀土Yb(III)的热力学和动力学机理，对该萃取剂的界面活性进行了深入的研究，并详细探讨了其从硫酸介质中萃取Ce(IV)时液/液界面的吸附参数及萃合物的聚集。此外，还考察了一种羧酸类萃取剂仲辛基苯氧基取代乙酸(CA-12)所组成的萃取有机相中W/O微乳液的热力学稳定性与结构参数。 1. 研究了Cyanex 923从硫酸介质中萃取与反萃Yb(III)的热力学。考察了一些影响萃取与反萃的条件，如：酸度、盐析剂、温度、反萃剂种类等，得出了萃取机理与热力学函数，为分离Yb(III)与其它稀土元素提供了有用的参数。 2. 研究了Cyanex 923 从硫酸体系中萃取Yb(III)的动力学，通过考察搅拌强度、比界面积、温度、反应物浓度等各种因素对萃取速率的影响，确定其对Yb(III) 的萃取动力学为扩散控制过程，反应主要在液/液界面进行，控制步骤为反应物种通过界面凝滞膜的界面扩散过程，并推导出了萃取速率经验式。 3. 考察了温度、离子强度、酸度、添加剂和不同稀释剂对萃取剂Cyanex 923在Cyanex 923-稀释剂/Na2SO4-H2SO4界面的界面活性的影响，得到了Cyanex 923在不同条件下的界面吸附参数，对萃取剂界面活性与萃取动力学的关系进行了讨论。 4.考察了Cyanex 923-正庚烷/Ce(IV)-H2SO4 萃取体系在液/液界面的吸附参数，重点研究了体系的界面活性物种、萃合物聚集造成的界面现象及其对溶剂萃取过程的影响，详细地研究了Ce(IV)和H2SO4的萃取对萃取体系一些物化性质的影响,观测到了萃取体系中反胶束的存在。 5. 研究了皂化CA-12—添加剂组成的萃取有机相中W/O微乳液的热力学稳定性，考察了皂化率、电解质本性与浓度、pH值、温度对体系最大加溶水量的的影响，并考查了不同添加剂与含水量时微乳液形成的热力学函数及结构参数。

离子液体在铈（IV）钍及稀土（III）萃取分离中的应用研究

本文对1-辛基-3-甲基咪唑六氟磷酸盐离子液体（[C8mim]PF6）在包头稀土矿分离钍以及攀西矿分离铈工艺中的应用作了初步探索。论文首先研究了伯胺N1923溶于离子液体对硫酸体系钍的萃取分离行为，考察了酸度、盐析剂浓度、萃取剂浓度等对N1923/IL萃取钍的影响，并与庚烷体系的萃取规律作了对比。在此基础上对萃取机理进行了探讨，提出了不同于分子溶剂体系的萃取机理，认为N1923/IL在水相有硫酸钠作为盐析剂时对钍的萃取为“胶束增溶”萃取机理。此外，钍对稀土的分离考察结果认为，虽然N1923/IL对钍的萃取效率降低，但在一定条件下钍对稀土仍能保持较高的分离系数。由此本文对N1923/IL应用于钍的分离实践作了初步评估。 论文的另外一部分工作研究了纯[C8mim]PF6及其与2-乙基己基膦酸二（2-乙基己基）酯（DEHEHP）的混合体系对硝酸铈（IV）的萃取性能。研究发现纯[C8mim]PF6本身对硝酸铈（IV）有良好的萃取选择性，机理考察结果认为铈（IV）的萃取是由于Ce4+离子在富硝酸根溶液中形成络阴离子Ce(NO3)62-并与离子液体的阴离子PF6—发生交换的结果。一种新型含铈离子液体[C8mim]2Ce(NO3)6的合成进一步证实了这一机理。反萃考察发现被萃入离子液相的铈（IV）用水可完全反萃，且萃取和反萃过程中因离子交换机理导致的离子液体流失可以通过添加适量离子液体组分的方法予以抑制。此外，本文考察了DEHEHP溶于[C8mim]PF6对于含氟硝酸体系铈（IV）的萃取行为，发现在一定条件下DEHEHP对铈（IV）的萃取能获得与分子溶剂中等同的萃取机理。在此基础上，采用DEHEHP/IL从氟碳铈矿分解液中进行分离铈和氟的研究，获得纯度为99.9%以上的纳米CeF3产品。由此我们提出一个将离子液体应用于攀西氟碳铈矿铈钍稀土分离流程的模型，为离子液体在稀土清洁分离流程中实现溶剂绿色化的目标提供了一个范例。

Upconversion luminescence of Y2O3 : Er3+, Yb3+ nanoparticles prepared by a homogeneous precipitation method

Y2O3: Er3+, Yb3+ nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3:Er3+,Yb3+ nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to H-2(11/2), S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) transitions of the Er3+ ion, respectively.

Synergistic extraction and recovery of Cerium(IV) and Fluorin from sulfuric solutions with Cyanex 923 and di-2-ethylhexyl phosphoric acid

Synergistic extraction and recovery of Cerium(IV) (Ce(IV)) and Fluorin (F) from sulfuric solutions using mixture of Cyanex 923 and di-2-ethylhexyl phosphoric acid (D2EHPA) in n-heptane have been carried out. in order to investigate the synergistic extraction of Cyanex 923 + D2EHPA, extraction Ce(IV), F, Ce(III) and Ce-F mixture solution using D2EHPA or Cyanex 923 as extractant alone were studied firstly, and then Synergistic extraction of Ce(IV), F and Ce(IV)-F mixture solution with D2EHPA + Cyanex 923 were carried out. The largest synergistic coefficient of Ce(IV) is obtained at the mole fraction X-Cyanex (923) = 0.8. The synergistic enhancement coefficients (R-max) obtained for Ce(IV) are 23.12 in Ce(IV) solution, and in Ce-F mixed solution R-max for Ce(IV) and F are 2.24 and 3.25 respectively.

The separation of Cerium(IV) from nitric acid solutions containing Thorium(IV) and Lanthanides(III) using pure [C(8)mim]PF6 as extracting phase

The extraction behavior of Ce(IV) along with Th(IV) and Ln(III) (Ln = Ce, Gd, Yb) nitrate by pure ionic liquid, [C(8)mim]PF6, was investigated. [C(8)mim]PF6 alone showed good extraction ability for Ce(IV), while it was slight for Th(IV) and negligible for Ln(III). The extraction behavior of Ce(IV) by [C(8)mim]PF6 was particularly studied, and the most probable extraction mechanism proposed was the anion exchange mechanism. Moreover, the stripping of Ce(IV) from IL phase was also investigated. The Ce(IV) in IL phase can be quantitatively recovered by water.

Silica Materials Doped with Bifunctional Ionic Liquid Extractant for Yttrium Extraction

Two new silica-based organic-inorganic hybrid materials (B104SGs and O104SGs) doped with a binary mixture of imidazolium and phosphonium ionic liquids have been synthesized and used as sorbents in batch system for rare earths (RE) separation. Imidazolium ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate (C(4)mim(+)PF(6)(-)) or 1-octyl-3-methylimidazolium hexafluorophosphate (C(8)mim(+)PF(6)(-)) acted as porogens to prepare porous materials and additives to stabilize extractant within silica gel.

Solvent impregnated resin prepared using task-specific ionic liquids for rare earth separation

A novel bifunctional task-specific ionic liquid (TSIL), i.e. [trialkylmethylammonium][sec-nonylphenoxy acetate] ([A336] [CA-100]) was impregnated on intermediate polarized XAD-7 resin, and the prepared solvent impreganated resin (SIR) was studied for rare earth (RE) separation. Adsorption ability of the SIR was indicated to be obviously higher than that prepared by [A336][NO3] because of the functional anion of [A336][CA-100]. Adsorption kinetics, adsorption isotherm, separation and desorption of the SIR were also studied.