Pr3+/Yb3+共掺碲酸盐玻璃发光特性的研究

根据Pr3 /Yb3 共掺碲酸盐玻璃在 980nm附近的吸收谱及 1.3 1μm处的发射谱 ,研究了玻璃样品光谱特性随稀土离子浓度变化的规律。结果表明 :在Yb3 离子浓度不变的情况下 ,1.3 1μm处的发光随着Pr3 离子浓度的增加 ,其强度先增后减 ,并在浓度为 0 .15mol%时达到最大值 ,同时根据Judd -Ofelt理论计算了稀土离子的光辐射特性     

(Ce-Zr)mA1-mO2复合氧化物的制备及其表征

以碳酸铵为沉淀剂,采用共沉淀法制备铈锆、铈锆镧、铈锆镨复合氧化物,通过X射线衍射(XRD)、BET法和程序升温还原(TPR)等手段对复合氧化物进行了表征,研究了高温焙烧条件下不同铈锆摩尔比和掺杂镧镨对复合氧化物的结构和性能的影响,并初步分析了掺杂La和Pr的作用机理.结果表明, Ce0.76Zr0.24O2在高温焙烧后仍然保持着立方相的固溶体结构,衍射峰没有发生分裂,有着比较好的高温热稳定性;掺杂La和Pr以后均能在一定程度上提高氧化物的热稳定性.     

纳米粉末Ca_(0.8)Ba_(0.2)TiO_3:Pr的制备与表征

采用溶胶—凝胶法合成Ca0.8Ba0.2TiO3:Pr纳米粉末,分别应用XRD、SEM和荧光分光光度计对样品的结构、形貌和光学特性进行表征。结果表明,纳米粉末Ca0.8Ba0.2TiO3:Pr形状近似为球形,在900℃煅烧8h所得样品的激发主峰位于323nm,发射主峰在612nm处,对应Pr3+的1 D2→3 H4跃迁,并且,在900℃时样品的初始发光强度和余辉时间都是最高的。     

QoS组播路由问题的多目标规划模型研究

该文在对比QoS组播路由问题几种表述模型的基础上,提出了基于多目标规划的新模型,讨论了该模型的求解方法;同时,采用Prüfer编码,提出了求解该模型的遗传算法,并分析了该算法的复杂性。文中还给出了部分关键算法的自然语言描述。     

The influences of stoichiometry on the sintering behavior,optical and scintillation properties of Pr:LuAG ceramics

Sintering aids may enter the host lattice, create defects, and seriously deteriorate the scintillation properties of ceramic scintillators. In this study, the 0.3at%Pr:LuAG ceramics with different excess of Lu were fabricated by the solid-state reactive sintering without aids. The influences of stoichiometry on the sintering behaviors, optical and scintillation properties of the ceramics are systematically studied. The results show that the stoichiometric ceramics experience an abnormal grain growth during sintering. The Lu excess can restrain the abnormal grain growth of the ceramics because of the impurity drag effect. The excess Al₂O₃ as optical scattering centers, can also pin in the grain boundary to limit the fast migration of the grain boundaries. The light yield value of the as-sintered ceramics decreases with the increase of Lu content. After air-annealing, the ceramics with appropriate excess of Lu can achieve better optical quality and higher light yield compared to the stoichiometric Pr:LuAG ceramics.     

Optimizing the preparation of Ni-Ce-Pr catalysts for efficient hydrogen production by n-dodecane steam reforming

Nowadays, the development of fuel cell is getting more and more inseparable from the production of hydrogen. Long-chain hydrocarbons steam reforming is a feasible way for hydrogen supply. Herein, various nickel-ceria-praseodymium (Ni-Ce-Pr) catalysts have been prepared by a sol-gel method. Multiple parameters during catalyst preparation, including the amount of Ni, the content of doped Pr and the calcination temperature, were systematically studied for tuning the catalytic performance for n-dodecane steam reforming in a fixed-bed reactor under 15 mL/g_cat·h at 600°C and water-to-carbon molar ratio of 2 at 0.1 MPa. Reaction data showed that both the amount of Ni and the content of doped Pr will greatly affect the n-dodecane conversion and hydrogen production. Additionally, the calcination temperature during catalyst preparation showed a big influence on its performance for n-dodecane steam reforming. After optimization, 10Ni-CePr₂-600 exhibits the highest activity and stability for n-dodecane steam reforming, accompanying with the lowest rate of coke deposition (0.015 g_c/g_cat·h). The structure and oxygen vacancy of the catalyst was characterized by H₂-TPR, Raman, and X-ray photoelectron spectroscopy (XPS). The superior activity and stability of 10Ni-CePr₂-600 are ascribed to the strong interaction between NiO and support along with abundant oxygen vacancies in the Pr-doped ceria.     

High pressure spectroscopy of Pr in LiNbO3

Absorption, emission, and luminescence excitation spectra of the LiNbO₃ crystal doped with 0.5% Pr³⁺ and 0.8% Yb³⁺ are presented. Additionally the photoluminescence spectra at high pressure have been measured. Hydrostatic pressures up to 135 kbar were applied with a diamond anvil cell. Absorption of the Pr³⁺:LiNbO₃ crystal is characterized by the strong threshold at about 400 nm, related to the band-to band-transitions and the sharp structure in the visible region attributed to the transitions to ³P_J and ¹D₂ levels of Pr³⁺ ion. After the 488 nm excitation the yellow emission related to the ¹D₂→³H_J transition of Pr³⁺ have been observed when the ³P₀ emission has not been detected. The excitation spectra of the ¹D₂ luminescence consist of the sharp lines related to the ³H₄→³P_J (J=0, 1, 2) transitions and two broad bands peaked at 340 and 400 nm related probably to the bound exciton. The ¹D₂→³H_J emission shifts with pressure toward the lower energies with the rate of −2.4 cm⁻¹ kbar⁻¹. Additionally, for higher pressures the ¹D₂ emission is considerably quenched. This is explained as being due to the decrease of the energy of the bound exciton with pressure which results in the higher nonradiative depopulation rate of the ¹D₂ state.     

Production and quality analysis of Pr55gag particles produced in baculovirus-infected insect cells

In this work Sf-9 cells previously adapted to SF900II and EXCELL 401 serum-free media (SFM) were grown and infected at different agitation rates in order to study the effects of power input upon cell growth, infection and production of Pr55gag particles in both SFM. Maximum cell concentration increased from 3×10⁶ to 6×10⁶ cells cm⁻³ and 6·5×10⁶ cells cm⁻³ when the agitation increased from 80 to 250 rpm or sparged aeration (0·01 vvm at 170 rpm) is used, clearly indicating that cell growth is limited by gas transfer. The specific productivity increased 3·5-fold when the agitation rate was increased from 80 to 170 rpm, indicating that in SFM cell infection is also limited by gas transfer. The highest product concentration was obtained in SF900II at 120 h post-infection (hpi). The product quality analysis showed that SF900II is the best medium for production of Pr55gag particles and that a careful optimisation of the harvest time is required. The maximum product titre was obtained at 120 hpi, 48 h after the achievement of the highest quality. © 1998 SCI     

Superconducting and non-superconducting PrBa2Cu3O7

Superconducting properties of Pr123 and microscopic structural differences between the superconducting and non-superconducting Pr123 crystals are reviewed. It is shown that the variety of physical properties of Pr123 is closely related to Cu deficiency at the chain site and our experimental results are consistently explained with a model that the Pr 4f-O 2p hybridization forms a narrow band and carriers are localized by a kind of atomic disorder in non-superconducting crystals.     

A noticeable effect of Pr doping on key optoelectrical properties of CdS thin films prepared using spray pyrolysis technique for high-performance photodetector applications

High-quality thin film-based photodetectors containing praseodymium doped cadmium sulfide (Pr:CdS) were fabricated through spray pyrolysis and studied for various opto-electrical applications. Field emission electron microscopy (FE-SEM) revealed that the prepared films were highly compacted with an extremely fine nanostructure without any pinhole or crack. X-ray diffraction and FT-Raman spectroscopy studies confirmed the single hexagonal phase of all the films. The crystallite size was found to lie between 19 and 32 nm. Optical spectroscopy revealed that the fabricated films have low absorbance and high transmittance (in range of 70–80%). The energy gap was found to lie in the range of 2.40–2.44 eV. The PL spectra contained an intense green emission band at ~531 ± 5 nm (2.33 eV), and its intensity was enhanced by increasing the Pr doping content in CdS. The dark and photo currents of CdS increased by approximately 950 and 42 times, respectively with the addition of 5.0 wt% Pr. The responsivity (R) and specific detectivity (D*) were remarkably enhanced to 2.71 AW^-1 and 6.9 × 10¹¹ Jones, respectively, for the 5.0 wt% Pr:CdS film. The external quantum efficiency (EQE) of 5 wt% Pr:CdS films was 43 times that of pure CdS films, and the on/off ratio was 3.95 × 10² for 5.0 wt% Pr:CdS film. Its high R, D*, and EQE values, and photo-switching behavior make Pr:CdS a good contender for high quality photodetector applications.