Red shift of the energy of optical absorption of quantum dot arrays in conditions of dynamic stark effect

The absorption coefficient of quantum dot arrays in conditions of dynamic Stark effect is calculated. It is shown that when ω₁ > ω₀ a red shift of the energy of optical transitions takes place.     

a-Si ∶H/SiO2多量子阱材料制备及其光学性能和微结构研究

利用等离子体增强化学气相沉积技术制备了a-Si ∶H/SiO₂多量子阱结构材料.对a-Si ∶H/SiO₂多量子阱样品分别进行了3种不同的热处理,其中样品经1100 ℃高温退火可获得尺寸可控的nc-Si:H/SiO₂量子点超晶格结构,其尺寸与非晶硅子层厚度相当.比较了a-Si ∶H/SiO₂多量子阱材料与相同制备工艺条件下a-Si ∶H材料的吸收系数,在紫外/可见短波段前者的吸收系数明显增大,光学吸收边蓝移,说明该材料关键词：多量子阱量子限制效应光学吸收能带结构     

State-filling and magneto-photoluminescence of excited states in InGaAs/GaAs self-assembled quantum dots

We present the first radiative lifetime measurements and magneto-photoluminescence results of excited states in InGaAs/GaAs semiconductor self-assembled quantum dots. By increasing the photo-excitation intensity, excited state interband transitions up ton= 5 can be observed in the emission spectrum. The dynamics of the interband transitions and the inter-sublevel relaxation in these zero-dimensional energy levels lead to state-filling of the lower-energy states, allowing the quasi-Fermi level to be raised by more than 200 meV due to the combined large inter-sublevel spacing and the low density of states. The decay time of each energy level obtained under various excitation conditions is used to evaluate the inter-sublevel thermalization time. Finally, the emission spectrum of the dots filled with an average of about eight excitons is measured in magnetic fields up to 13 Tesla. The dependences of the spectrum as a function of carrier density and magnetic field are compared to calculations and interpreted in terms of coherent many-exciton states and their destruction by the magnetic field.     

Optical modulator using metal-oxide-semiconductor type Si ring resonator

Electric-field drive optical modulators using a Si ring resonator were fabricated on silicon-on-insulator (SOI) wafers. The fabricated resonators consisted of Si waveguides with width and thickness of 1.0 and 0.3 μm, respectively. In order to induce the linear electro-optic (EO) effect in the Si core layer, the strain was applied by covering the layer with Si₃N₄ film (0.26 μm thick) deposited by low pressure chemical vapor deposition (LPCVD) at 750 °C. The vertical electric-field was applied to the Si waveguide through the top and bottom cladding layers, and the optical output from the drop port at the resonance wavelength was measured. At a wavelength of 1501.6 nm, the optical modulation of 33% was obtained at 200V (electric-field at the silicon surface ∼3 × 10⁵ V/cm, nearly the breakdown field). The resonance wavelength was shifted toward the short wavelength side by applying both positive and negative voltages, this shift was explained by carrier concentration modulation. The linear EO effect in the Si core layer was not observed, presumably because the strain in the Si core layer was too small.     

包埋于氮化硅薄膜中的硅团簇的光致发光特性

采用等离子体增强化学气相沉积(PECVD)技术,在低温下制备了富硅氢化氮化硅薄膜。利用红外吸收(IR)谱,光电子能谱(XPS)和光致发光(PL)谱,研究了在不同温度下退火的薄膜样品的结构和发光特性。在经过低温退火的薄膜中观测到一个强的可见发光峰。当退火温度较高时,随着与硅悬键有关的发光峰消失,可见发光峰位发生了蓝移。讨论了退火对薄膜中硅团簇的形成及其对发光的影响。根据Raman谱,计算了氮化硅薄膜中硅团簇的尺寸大小。通过实验结果和分析,我们认为PL谱中较强的室温可见发光峰来自于包埋于氮化硅中的硅团簇。     

猫眼逆向调制自由空间激光通信技术的研究进展

猫眼逆向调制自由空间激光通信技术相比传统激光通信技术更具优势。本文介绍了逆向调制自由空间激光通信技术的原理和猫眼逆向调制终端的原理结构。综述了国内外猫眼逆向调制自由空间激光通信技术在调制器特性、猫眼光学系统和技术应用3个方面的研究现状。分析了猫眼逆向调制自由空间激光通信的关键技术。最后,展望了该项技术的应用前景。     

取代效应对脂滴检测NAPBr染料分子的双光子吸收和激发态性质影响的理论探究

双光子荧光染料分子在生物医学成像中具有广阔的应用前景,但取代效应对分子结构以及光物理性质影响的探求相对匮乏. 本文设计并研究了一系列脂滴检测染料分子,分析了分子的光学性质以及无辐射跃迁等. 通过分子内弱相互作用和电子- 空穴布居分析,阐述了其内在机理. 结果表明,所研究的分子均具有优良的光物理性能、高效荧光量子产量、大的斯托克斯位移以及显著的双光子吸收截面等. 本工作合理地解释了实验现象并阐述了取代效应对脂滴检测NAPBr染料分子的双光子吸收和激发态性质的影响,这为设计新型的高效有机分子提供了理论指导.     

The radiative lifetime and the optical absorption cross section measurements of neodymium

Using the technique of laser induced fluorescence, we have obtained the experimental results that the radiative lifetime of the ~7K_3~o state and the optical absorption cross section of the transition ~5I_4~e→~7K_3~o of neodymium are 675±50ns and (1.48±0.74)×10~(-13)cm~2 respectively.     

Silicon nanoparticles: Preparation,properties, and applications

Silicon nanoparticles have attracted great attention in the past decades because of their intriguing physical properties,active surface state, distinctive photoluminescence and biocompatibility. In this review, we present some of the recent progress in preparation methodologies and surface functionalization approaches of silicon nanoparticles. Further, their promising applications in the fields of energy and electronic engineering are introduced.     

一种新的芴类衍生物的三光子吸收诱导荧光和光限幅效应研究

通过对新合成的芴的一种具有对称性衍生物4-2-(7-(4-氨基苯乙烯基)-9,9-二(2-乙基己基)-9H-芴-2-)乙烯基)苯胺(BASF)的DMF溶液的研究,发现其具有很强三光子吸收频率上转换荧光发射特性,实验测出上转换荧光的波长范围是456—775nm,在510nm处的荧光强度与入射光强的三次方成正比.在0.03mol/L的浓度下就有明显的三光子吸收诱导的光限幅效应.非线性吸收系数和吸收截面分别为γ=4.34×10^-20cm³/W²和σ₃＝2.4×10^-39cm⁶/W².关键词：三光子吸收光限幅上转换荧光吸收截面     

Donor impurity-related photoionization cross section in GaAs cone-like quantum dots under applied electric field

The donor impurity-related electron states in GaAs cone-like quantum dots under the influence of an externally applied static electric field are theoretically investigated. Calculations are performed within the effective mass and parabolic band approximations, using the variational procedure to include the electron–impurity correlation effects. The uncorrelated Schrödinger-like electron states are obtained in quasi-analytical form and the entire electron–impurity correlated states are used to calculate the photoionisation cross section. Results for the electron state energies and the photoionisation cross section are reported as functions of the main geometrical parameters of the cone-like structures as well as of the electric field strength.     

纳米锗颗粒镶嵌薄膜的吸收光谱研究

用离子束溅射技术和热处理方法,制备出颗粒尺寸和镶嵌密度均可控制的高质量Ｇｅ－ＳｉＯ２纳米颗粒镶嵌薄膜,在室温下测量了不同粒度纳米锗颗粒镶嵌薄膜样品的吸收光谱,观测到在可见光区有较强的光吸收和吸收带边蓝移。研究表明：镶嵌在经缘介质薄膜中的纳米锗颗粒的能量带是量子化的,随着纳米锗粒子平均尺寸的减小,其吸收带隙增加,吸收带边蓝移的程序相应增大。     

高局域性的可调硅基混合表面等离子体光相位调制器

设计和分析了一种可调硅基混合表面等离子体相位调制器.表面等离子体的引入打破了衍射极限的限制,使光场局域在一个纳米尺寸范围.该调制器的实现采用了两种原理:硅材料的等离子体色散效应以及聚合物的电光效应.由于器件结构的电容和寄生电阻较小,RC响应时间为3.77 ps,调制带宽大约100 GHz.当外加2.5V的驱动电压时,该...     

非晶Si/SiO2超晶格结构的交流电致发光

设计并用磁控溅射方法制备了非晶Ｓｉ／ＳｉＯ２超晶格结构,以高纯多晶Ｓｉ为靶材,当以Ａｒ＋Ｏ２为溅射气氛时,得到ＳｉＯ２膜,仅以Ａｒ为气氛时,得到Ｓｉ膜。重复地开和关Ｏ２气,便交替地得到ＳｉＯ２和Ｓｉ膜。衬底在靶前往返平移,改变平移的速度或者改变溅射的功率,可以控制膜的厚度。通过透民镜的照片可以看出ＳｉＯ２和Ｓｉ膜具有均匀的周期结构,用低角Ｘ－射线反射谱表征了超晶格的周期结构和各层的厚度。透射光谱表     

Electronic states and shapes of silicon quantum dots

A curviform surface breaks the symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in the bandgap. The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides localized levels in bandgap and its bonding energy is shallower than that on the facet. The red-shifting ofthe photoluminescence spectrum on smaller silicon quantum dots can be explained by the curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided by the curved surface effect.     

硅量子点的形状及其弯曲表面效应

硅量子点的弯曲表面引起系统的对称性破缺, 致使某些表面键合在能带的带隙中形成局域电子态.计算结果表明:硅量子点的表面曲率不同形成的表面键合结合能和电子态分布明显不同. 例如, Si–O–Si桥键在曲率较大的表面键合能够在带隙中形成局域能级, 而在硅量子点曲率较小的近平台表面上键合不会形成任何局域态, 但此时的键合结合能较低. 用弯曲表面效应(CS)可以解释较小硅量子点的光致荧光光谱的红移现象. CS效应揭示了纳米物理中又一奇妙的特性. 实验证实, CS效应在带隙中形成的局域能级可以激活硅量子点发光.关键词：硅量子点弯曲表面效应表面键合局域能级     

氧分压对磁控溅射制备ZnO薄膜的结构及光学特性的影响

采用射频反应磁控溅射法在玻璃衬底上成功制备出具有c轴高择优取向的ZnO薄膜,利用X射线衍射及紫外-可见吸收和透射光谱研究了氧分压变化对ZnO薄膜的微观结构及光吸收特性的影响。结果表明,当工作气压恒定时,用射频反应磁控溅射制备的ZnO薄膜的生长行为主要取决于成膜空间中氧的密度,合适的氧分压能够提高ZnO薄膜的结晶质量;薄膜在可见光区的平均透过率达到90%以上,且随着氧分压的增大,薄膜的光学带隙发生了一定程度的变化。采用量子限域模型对薄膜的光学带隙作了相应的理论计算,计算结果与对样品吸收谱所作的拟合结果符合较好,二者的变化趋势完全一致,表明ZnO纳米晶粒较小时,薄膜光学带隙的变化与量子限域效应有很大关系。