共查询到20条相似文献,搜索用时 15 毫秒
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《Fiber and Integrated Optics》2007,26(3):147-157
This paper investigates the performance of a given gigabit optical code division multiple access (O-CDMA) network for two distinct families of two-dimensional (2-D) codes. The purpose of this analysis is to provide additional information regarding code adequacy to a given system availability so that performance optimization can be more efficiently carried out. The analysis takes into account construction aspects of the codes as well as dispersive and nonlinear effects in the single-mode fiber (SMF), such as group velocity dispersion (GVD), polarization mode dispersion (PMD), self-phase modulation (SPM), and cross-phase modulation (XPM). The analysis focuses on four different transmission rates, i.e., 1.25, 2.5, 5, and 10 Gbit/s, and describes how signal degradations impact the performance of the network. The simulations are carried out for a back-to-back system and for a 50-km dispersion-compensated fiber-optic link. 相似文献
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Exploration of structural,optical, and photoluminescent properties of (1-x)NiCo2O4/xPbS nanocomposites for optoelectronic applications 下载免费PDF全文
The (1-x)NiCo2O4/xPbS (0≤ x≤ 0.2) nanocomposite samples are synthesized using the hydrothermal and thermolysis procedures. The different phases developed in the obtained nanocomposite samples are accurately determined using the x-ray diffraction technique equipped with a line-detector. The percentage of the formed phases (NiCo2O4 (NCO), PbS, PbSO4), structural and microstructure parameters are determined using Rietveld quantitative phase analysis. The transmission electron microscope (TEM) images and Rietveld analysis reveal almost isotropic particle size in the nano range with a very narrow size distribution. The obtained phase percentage of PbS and PbSO4 are smaller than nominated values (x) suggesting dissolving of some Pb and S ions into NCO which is then confirmed by the analysis of Fourier-transform infrared (FTIR) spectra of nanocomposite samples. The absorption spectra are modified upon doping NCO with PbS. The optical band gaps of the nanocomposites increase as the amount of PbS augments. The effect of alloying on extinction coefficient, refractive index, dielectric constant, optical conductivity, the intensity, and emitted color from the photoluminescence of the nanocomposite samples are also studied. The refractive index value of NCO and NCO-PbS nanocomposite samples exhibit normal dispersions. The photoluminescent measurements reveal that the NCO-PbS nanocomposites can emit a violet color. The improvement in the values of the nonlinear optical (NLO) parameters of pristine NCO at high frequencies or the nanocomposite samples at low frequencies, are made them used in NLO photonic devices. 相似文献
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N^+(N=Li,Na,K)对发光材料M3(M=Ca,Sr,Ba)Y2(BO3)4:Eu^3+光谱的影响 总被引:2,自引:0,他引:2
采用高温固相反应方法在空气中制备了M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 红色发光材料,测量结果显示,材料的主发射峰均位于613 nm处,监测613 nm发射峰时,所得材料的激发光谱相同。研究了Li ,Na 和K 对M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料激发与发射光谱的影响,结果显示,加入Li ,Na 和K 后,M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料的激发与发射光谱的峰值位置并不发生变化,但材料的激发与发射光谱的峰值强度均得到了不同程度的增强。在Li ,Na 和K 掺入浓度相同的条件下,研究发现,与加入Na 和K 时相比,加入Li 时,M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料的激发与发射光谱的峰值增强效果最明显。进而研究了Sr3Y2(BO3)4∶Eu3 材料发射峰强度随Li 掺杂浓度的变化情况,结果表明,随着Li 掺杂浓度的增大,Sr3Y2(BO3)4∶Eu3 材料发射峰强度先增大后减小,在Li 浓度为5 mol%时到达峰值,约为未掺杂时的两倍。 相似文献
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利用密度泛函和含时密度泛函理论研究了氧(O)和硫(S)原子掺杂的石墨相氮化碳(g-C_3N_4)_6量子点的几何、电子结构和紫外-可见光吸收性质.结果表明:掺杂后(g-C_3N_4)_6量子点杂质原子周围的C-N键长发生了一定的改变,最高电子占据分子轨道-最低电子未占据分子轨道(HOMO-LUMO)能隙显著减小.形成能的计算表明O原子取代掺杂的(g-C_3N_4)_6量子点体系更稳定,且O原子更易取代N3位点,而S原子更易取代N8位点.模拟的紫外-可见电子吸收光谱表明,O和S原子的掺杂改善了(g-C_3N_4)_6量子点的光吸收,使其吸收范围覆盖了整个可见光区域,甚至扩展到了红外区.而且适当的杂质浓度使(g-C_3N_4)_6量子点光吸收在强度和范围上都得到明显改善.通过O和S掺杂的比较,发现二者在可见光区对(g-C_3N_4)_6量子点的光吸收有相似的影响,然而在长波长区域二者的影响有明显差异.总体而言,O掺杂要优于S掺杂对(g-C_3N_4)_6量子点光吸收的影响. 相似文献
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采用高温固相法合成了白光LED用Ca8Mg(SiO4)4Cl2:Eu和Ca8Mg(SiO4)4Cl2:Eu,Dy绿色发光粉。研究发现:共掺Dy可以明显地提高Ca8Mg(SiO4)4Cl2:Eu发光粉的发光性能,表明Dy3+和Eu2+之间存在着能量传递过程。当Dy3+的最佳掺杂摩尔分数为0.02时,发光粉505nm处绿光发射的强度约提高12%。通过对Dy3+和Eu2+光谱特性的分析,Dy3+和Eu2+之间的能量传递机制可归因于无辐射交叉弛豫。 相似文献
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First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal 下载免费PDF全文
Zhang Peng Kong Chui-Gang Zheng Chao Wang Xin-Qiang Ma Yue Feng Jin-Bo Jiao Yu-Qiu Lu Gui-Wu 《中国物理 B》2015,24(2):24221-024221
The geometric structure,electronic structure,and optical properties of CdHg(SCN)4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation.The band gap of CdHg(SCN)4 crystal is calculated to be 3.198 eV,which is in good agreement with the experimental value 3.265 eV.The calculated second-order nonlinear optical coefficients are d_(14) = 1.2906 pm/V and d_(15) = 5.0928 pm/V,which are in agreement with the experimental results(d_(14)=(1.4 ±0.6) pm/V and d_(15)=(6.0 ±0.9) pm/V).Moreover,it is found that the contribution to the valence band mainly comes from Cd-4d,Hg-5d states,and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p,N-2p,and S-3p states.The second-order nonlinear optical effect of CdHg(SCN)_4 crystal results mainly from the internal electronic transition of(SCN)~-. 相似文献
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《Journal of Macromolecular Science: Physics》2013,52(5-6):657-665
Melting behavior in associating poly(4-vinylphenol)–N,N-dimethyloctadecylamine mixtures (PVPh-NDOA), which form comb-shaped aggregates, was investigated with various end functionality of the NDOA. Melting temperatures of the comb-shaped aggregates were depressed with slightly decreased end functionality of the surfactant. However, it was found that the repeating unit of PVPh and the dimethylamino group of NDOA formed 1:1 stoichiometric aggregates regardless of the decrement of the end functionality of the NDOA. In addition, it was shown that the excess surfactants, which did not have polar groups on the alkyl chain ends, act only as an impurity for the side-chain crystals of the PVPh-NDOA aggregates. 相似文献
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Optoelectronic characteristics of >9% efficient bilayered CuZnSn(S,Se)4 photovoltaic device 下载免费PDF全文
Wei Wu Nancy G. Tassi Yanyan Cao Jonathan V. Caspar Kaushik Roy‐Choudhury Lei Zhang 《固体物理学:研究快报》2015,9(4):236-240
Using binary and ternary chalcogenide nanoparticle solutions as precursors, a bi‐layered CZTSSe film is formed after being annealed in selenium atmosphere. Based on the CZTSSe film, a high efficiency thin‐film photovoltaic device (9.02% conversion efficiency) is made. Detailed characterizations of the device's performance and composition from XPS depth profiling are presented, and based on the results we discuss possible areas for further efficiency improvement. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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Synthesis and study the influence of yttrium doping on band structure,optical, non-linear optical and dielectric results for Ca12Al14O33 (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method 下载免费PDF全文
Ca12Al14O33(C12A7)and Y0.02Ca11.98Al14O33(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca12Al14O33(C12A7)and Y0.02Ca11.98Al14O33(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications. 相似文献
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基于第一性原理赝势平面波方法对伽马晶体CuCl, CuBr, CuI的体模量、体模量对压强的一阶偏导 数、电子结构、折射率等光学性质进行了计算.计算结果表明,广义梯度近似(GGA)下CuX(X = Cl, Br, I) 晶体的晶格常数与体模量的计算值与实验相差较小.与局域密度近似(LDA)相比, GGA更适合于 CuX(X = Cl, Br, I)晶体 的计算.这三者的价带都来源于Cu的3d态,导带部分主要来自Cu和卤素的s电子贡献,很少部分来自卤素的p电子 贡献.计算得到CuCl, CuBr, CuI的折射率分别为1.887, 2.015, 2.199,与应用Gladstone-Dale半经验关系得到 的结果符合得很好. 相似文献
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We first recall the main linear optical properties of semiconductor-doped glasses in the strong confinement regime. We then discuss the origin of the photodarkening effect and its consequences on the luminescence and absorption spectra. Photodarkening and, at high excitation intensity, Auger processes strongly modify carrier recombination as studied by time-resolved luminescence measurements. This is further supported by using nonlinear optical techniques such as optical phase conjugation. We finally recall the origin of the nonlinear response of such media in the resonant regime and the size dependence of the corresponding figure of merit. 相似文献
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在强场耦合图像中,采用双自旋-轨道耦合(SO)参量模型建立了过渡族3d2(3d8)离子的三角对称下全组态光谱能级和电子顺磁共振(EPR)公式.与经典的晶体场理论(仅考虑中心金属离子的自旋-轨道耦合作用)相比较,该公式还包括了配体离子的自旋-轨道耦合作用的贡献,这一模型在应用于计算共价性较强的晶体光谱和电子顺磁共振谱可得到合理的结果.作为验证,用完全对角化方法研究了品体NiX2(X=Cl,Br,I)的光谱和电子顺磁共振谱,结果表明,理论与实验很好地符合.建立的全组态谱能级和电子顺磁共振公式为更精确地计算光谱和电子顺磁共振谱提供了一条可行方法. 相似文献
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ABSTRACTHydrogen storage reactions on Ni ? C59X(X = B, N) heterofullerene are investigated by using the state-of-the-art density functional theory calculations. The Ni atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to five hydrogen molecules with average adsorption energies of (?0.94, ?0.48, ?0.33, ?0.25 and ?0.20 eV) per hydrogen molecule for Ni ? C59B, while (?1.20, ?0.60, ?0.41, ?0.28 and ?0.23 eV) per hydrogen molecule for Ni ? C59N. With no metal clustering, the system gravimetric capacities are expected to be as large as 10.87 and 10.85 wt % for 5H2NiC59B?and 5H2NiC59N, respectively. While the desorption activation barriers of the complexes 1H2 + C59X?(X = B, N)?are outside the Department of Energy domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH2 + C59X(X = B, N)(n = 2 ? 5) are inside this domain. The hydrogen storage of the irreversible 1H2 + NiC59X?(X = B, N) and reversible 2H2 + NiC59X?(X = B, N) interactions is characterised in terms of density of states and projected densities of states, pairwise and non-pairwise additivity, infrared, Raman, electrophilicity and molecular electrostatic potentials. 相似文献
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Min-Quan Kuang Hong-Kuan Yuan An-Long Kuang Hong Chen Li-Dan Wang 《Molecular physics》2017,115(20):2558-2564
The spin Hamiltonian parameters g and A for copper(II) in CuX4 (X = N, S, Cl and Br) tetrahedrons are theoretically investigated within a uniform model by utilizing the perturbation method and cluster approach for 3d9 ions suffering D2d symmetry in view of host structures and angular distortions in terms of a single parameter β. For all the studied polymers, the isotropy of g tensors gav and the hyperfine structure constant component A‖ are found, respectively, to undergo an increasing and decreasing trend with the enlarging average X–Cu–X angle β, while the obtained cubic crystal field parameter Dq and isotropic Fermi contact constant κ are experiencing a declining and growing tendency with the rising Cu–X bond length, respectively. The critical angle βc is concluded locating in the range of 109.471°–120° in which the g-isotropy value would reach the maximum, while the hyperfine structure factor might vanish that needs to be verified in future X-ray and EPR experiments. This work would be beneficial to the establishment of complete EPR and structure diagram for CuX4 complexes and the synthesis of new compounds possessing novel physical and chemical properties. 相似文献
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K2Ca2(SO4)3 microcrystalline pure, doped with Eu, Tb and co-doped with Eu, Tb was prepared by solid-state diffusion method. Nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by broadening of the XRD peaks using Scherrer's formula. The particle size of nanocrystalline powder material was approximately found to be around 20 nm. Thermoluminescence and photoluminescence were studied to see the effect of co-doping and particle size. Tb3+ co-doping decreases the intensity in the Eu2+ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The sensitivity of K2Ca2(SO4)3:Eu,Tb microcrystalline phosphor was around 15 times more than LiF-TLD 100 and 7 times more than CaSO4:Dy. A high temperature peak (615 K) was observed in case of the nanoparticles, which was attributed to a particle size induced phase transition. This was confirmed by differential scanning calormetry measurements. The decrease in the sensitivity in case of nanoparticles is attributed to the particle size effect i.e. volume to surface ratio. Theoretical analysis of the glow curves was done by glow curve convolution deconvolution method to calculate trapping parameters of various peaks. 相似文献