Near infrared fluorescence and energy transfer in Ce/Nd Co-doped CaxSr1−xS

Novel near infrared (NIR) phosphors Ca_xSr_1−xS:Ce³⁺,Nd³⁺ were synthesized by a solid state reaction. The NIR emission was realized through an efficient absorption by the allowed 4f-5d transition of Ce³⁺ and efficient energy transfer to Nd³⁺ via well-matched energy levels. Ce³⁺ and Nd³⁺ content in CaS/SrS was optimized. It was found that CaS:Ce³⁺,Nd³⁺ gave much stronger NIR emission than that of SrS:Ce³⁺,Nd³⁺. Further studies on Ca_xSr_1−xS:Ce³⁺,Nd³⁺ indicated that both visible emission of Ce³⁺ and NIR emission of Nd³⁺ were observably affected by Ca/Sr ratio. The energy transfer efficiency, which can be estimated from fluorescence lifetime of Ce³⁺, increased from 52% to 74% for the Ca_xSr_1−xS:Ce³⁺,Nd³⁺ (x=0 to 1) series, accompanied with a shift of maximal emission wavelength of Ce³⁺ from 482 to 505 nm. The results showed that overlap between emission spectrum of Ce³⁺ and excitation spectrum of Nd³⁺ plays an important role in the energy transfer efficiency, and Ce³⁺ emitting in green or blue-greenish region sensitized the Nd³⁺ NIR fluorescence emission more efficiently than that in blue region.     

Investigation of resonant properties of metal core–shell nanoparticles using T-matrix calculations

Using T-matrix method, plasmon resonance properties of metal core–shell nanoparticles are systematically investigated. It is shown that dielectric/metal core–shell structure may be excited stronger at resonance than metal/dielectric and hetero-metal ones, but the resonance states are extremely sensible to the layers thickness. For three-layer nanospheres, resonance properties will be dominated by a sub-10 nm silver outermost shell, while only weakened by a silica one. Finally, tiny eccentric distance between the centers of core and shell in eccentric two-layer nanoparticles may fundamentally change the resonance mode of nanoparticles, and results in higher local electrical field enhancement than concentric nanospheres.     

Synthesis and optical properties of 10 mol% Ce, 5 mol% Tb co-doped KGdF4 and GdF3 submicro/nanocrystals

By controlling the pH values of prepared solutions, the 10 mol% Ce³⁺, 5 mol% Tb³⁺ co-doped KGdF₄ (synthesized with pH = 3) and the 10 mol% Ce³⁺, 5 mol% Tb³⁺ co-doped GdF₃ (synthesized with pH = 1) submicro/nanocrystals have been synthesized based on a citric acid assisted hydrothermal method. For comparison, the samples synthesized by co-precipitation method (without hydrothermal treatment) with pH = 3 and 1 were also collected. The X-ray diffraction data illustrate that the hydrothermal treated KGdF₄ sample crystallizes in the cubic phase and the GdF₃ sample crystallizes in the orthorhombic phase. However, the samples synthesized by co-precipitation method with pH = 3 and 1 are both cubic phase KGdF₄. The field emission scanning electron microscopy images suggest that the hydrothermal treated KGdF₄ submicro/nanocrystals present spherical morphology and the GdF₃ submicrocrystals are rhombic-shaped. And the photoluminescence excitation and emission spectra as well as the luminescent dynamic curves demonstrate the difference in optical properties of the two hydrothermal treated samples.     

Non-uniformity correction algorithm for IRFPA based on motion controllable micro-scanning and perimeter diaphragm strips

Non-uniformity correction is the key issue for the image quality improvement of infrared focal panel array (IRFPA) imaging. A non-uniformity correction (NUC) algorithm for IRFPA based on motion controllable micro-scanning platform and perimeter diaphragm strips is presented. We initially execute one-point calibration to the perimeter detectors, then based on controllable motion of adjacent frames, a special algebraic algorithm is proposed to transport the calibration of the perimeter detectors to those interior un-corrected ones. In this way, the bias parameter of the whole field of view (FOV) is calculated. The algorithm can be easily combined with sub-pixel imaging, thereby improving the quality of thermal imaging system (image spatial resolution and uniformity). All calculations are algebraic, with a low computation load. The algorithm can realize adaptive one point calibration without covering the central FOV rapidly. Experiments on simulated infrared data demonstrate that this algorithm requires only dozens of frames to obtain high quality corrections.     

The system design and assemble for the high resolution telescope system with segmented aperture

A design method along with its results, for a space optical system with high resolution and wide field of view, is described. Such optical systems can be used in the infrared as well as visible configurations. The proposed design is based on an on-axis Ritchey-Chrétien system with corrected lens element while the primary mirror is a segmented aperture. Here the on-axis concept allows wide-field enabling a variety of observations designed for the multi-object spectrometer instruments, optimized for low scattering and low emission of light. The use of segmented mirrors in the optical system allows adopting any method for its fabrication purposes. Segment results are discussed and the image quality of the design based on these results is evaluated in this paper.     

基于光子筛的软X光谱仪

 介绍了采用新型软X光谱学光子筛作为分光元件的软X光谱仪的原理和结构参数设计。新谱仪理论测量范围为100 eV~2 keV,光谱分辨力达0.35 nm。应用该谱仪在SILEX-Ⅰ装置上测量了飞秒激光与固体铜靶相互作用产生的X射线发射谱。实验结果表明,该谱仪主要性能指标达到设计要求,适合于激光与等离子体相互作用产生的软X射线研究。     

40Gbps NRZ在基于宽带CFBG色散补偿的G.652光纤中无电中继传输500km

在基于宽带CFBG色散补偿的G.652光纤中,40Gbps NRZ码无电中继传输500km,在误码率BER=10(-10)下的功率代价约为2.2dB,积累1h的误码率为7.3×10(-12).传输系统中采用的CFBG的3dB带宽约为1.2nm,中心波长处时延纹波小于25ps,反射谱纹波小于2dB,差分群时延小于1ps....     

Intersubband transitions in Al0.82In0.18N/GaN single quantum well

The influence of the width of a lattice-matched Al_0.82In_0.18N/GaN single quantum well (SQW) on the absorption coefficients and wavelength of the intersubband transition (ISBT) has been investigated by solving the Schrödinger and Poisson equations self-consistently. The wavelength of 1—2 ISBT increases with L, the thickness of the single quantum well, ranging from 2.88 μm to 3.59 μm. The absorption coefficients of 1—2 ISBT increase with L at first and then decrease with L, with a maximum when L is equal to 2.6 nm. The wavelength of 1—3 ISBT decreases with L at first and then increases with L, with a minimum when L is equal to 4 nm, ranging from approximately 2.03 μm to near 2.11 μm. The absorption coefficients of 1—3 ISBT decrease with L. The results indicate that mid-infrared can be realized by the Al_0.82In_0.18N/GaN SQW. In addition, the wavelength and absorption coefficients of ISBT can be adjusted by changing the width of the SQW.     

Level structures in the 114 In nucleus

High-spin states in ¹¹⁴In were populated using the reaction ¹¹⁰Pd(⁷Li, 3n)¹¹⁴In at a beam energy of 26MeV. The level scheme of ¹¹⁴In consisting of six bands is established up to excitation energy ～ 5MeV and spin ～ 17 ? with the addition of 58 new transitions and their configurations are discussed. The intense positive-parity dipole cascade may be interpreted as shears band based on $ \pi$ [(g _9/2)^-1] ? $ \nu$ [(g _7/2/d _5/2)(h _11/2)²] configuration. The $ \Delta$ I = 2 bands based on proton excitation have been observed in ¹¹⁴In for the first time.     

Nature of M-Ng interaction in the MNg 4 2+ (M = Cu, Ag and Au; Ng = He and Ne) molecules: ab initio calculations

Quantum chemical calculations of the structure and stability of MNg ₄ ²⁺ (M = Cu, Ag and Au; Ng = He and Ne) series at the CCSD(T) theoretical level are performed. The interaction mechanism is investigated using the natural bond orbital (NBO) and electron density analyses. The analyses of the electron density show the weak electrostatic interaction in the system.