CdS0.1Se0.9纳米晶体共振电吸收谱的线形分析

采用电调制技术在室温下测量了 Cd S0 .1 Se0 .9纳米晶体的电吸收谱 ,并对电吸收谱线形进行了分析。纳米晶体与第一个吸收峰有关的电吸收谱结构具有吸收系数对能量的二阶微商特征 ,表明第一激发态在电场作用下以吸收谱线的宽化为主 ,而纳米晶体尺寸不单一是吸收谱线宽化的主要因素。共振电光响应信号的峰值位置、过零点位置以及电吸收谱的线形几乎不随外电场强度而变化 ,信号幅度随外电场强度的平方线性增加。 Cd S0 .1 Se0 .9纳米晶体的电光效应是Kerr效应 ,纳米晶体具有三阶非线性光学极化率 Χ( 3 )。     

Co2+:ZnAl2O4晶体电子光谱及其2E态双重谱线结构的Jahn-Teller效应研究

在中间场耦合图象中,利用Racak不可约张量算符法和Wigner－Eckart定理,建立了3d⁷(C_3v)电子组态的完全能量矩阵;利用该矩阵研究了Co²⁺:ZnAl₂O₄晶体的电子光谱,理论与观测十分吻合．首次定量地解释了2E态的双重谱线结构,并从理论上预言了⁴A₂基态2.93cm^-1的零场分裂(ZFS)．研究结果定量地表明,Jahn－Teller效应所致Co²⁺:ZnAl₂O₄晶体Co²⁺中心局域结构的畸变假设是合理的．     

FeSiF66H2O晶体的基态能级和零场分裂参量

由单晶的中子衍射方法得到FeS_iF₆6H₂O的晶体结构,这种晶体结构可以用S_iF^6-和Fe(H₂O)⁺⁺两个离子来描述,而局域三角对称的Fe(H₂O)⁺⁺离子反映了这种晶体的主要光谱性质利用不可约张量的理论,构成了晶体场和自旋轨道相互作用哈密顿完全对角化矩阵因此,由完全对角化的晶体场和自旋轨道相互作用哈密顿矩阵和电子顺磁共振的理论公式来求出晶体FeS_iF₆6H₂O中Fe²⁺离子的电子顺磁共振零场分裂参量D和Fa并研究了低自旋³L态对电子顺磁共振(EPR)零场分裂参量的贡献结果显示低自旋³L态对电子顺磁共振的零场分裂参量的贡献是较强的理论计算的结果与实验值是相符的.     

双横向电光克尔效应

理论分析了克尔(Kerr)介质在两个横向电场作用下的电光调制特性.并由此确定了具有双横向电光克尔效应的光学材料种类.采用折射率椭球方法分析可知,各向同性克尔介质和一些晶体在横向外加电场作用下,其电光相位延迟与外加电场幅值的平方成正比,与电场方向无关;而其电光双折射主轴方位角与外加电场的方向角成正比,与电场幅值无关,称这种电光调制特性为双横向电光克尔效应.理论分析结果表明,排除兼有泡克耳斯(Pockels)效应和电致旋光效应的材料,立方晶系432,m3m点群和六角晶系6/mmm点群的晶体以及所有各向同性光学介质具有双横向电光克尔效应.目前已有克尔常数较大的陶瓷玻璃材料研制成功,将有力地促进双横向电光效应在光学各领域中的广泛应用.     

精确研究NbN分子d1Σ+—b1Σ+电子态跃迁的P线系发射光谱

本文利用最近建立的能精确求解双原子分子P线系发射光谱的物理新公式, 研究了NbN分子从电子态d¹Σ⁺向b¹Σ⁺电子态跃迁中(1,1)跃迁带的P支发射光谱. 获得的计算结果不仅很好地重现了已知低转动态的实验谱线数据, 同时也预言了该跃迁带包含转动量子数J=80在内的高振转激发态的精确P线系发射光谱. 该方法在理论上为实验技术难以精确测量的双原子分子体系提供了一种获得精确的高激发态谱线数据的物理新方法. 从而可以为那些需要NbN分子高激发态跃迁谱线的研究工作提供必要的数据.     

Mg:Fe:LiNbO3晶体的生长及光学性能研究

在Fe:LiNbO₃中掺进MgO和Fe₂O₃以提拉技术生长Mg:Fe:LiNbO₃晶体.对晶体进行极化和还原处理.测试晶体的吸收光谱,Mg:Fe:LiNbO₃晶体吸收边相对Fe:LiNbO₃晶体发生紫移.测试晶体的红外光谱,Mg:(5 mol%)Fe:LiNbO₃晶体OH^-吸收峰由Fe:LiNbO₃晶体的3482 cm^-1移到3534 cm^-1.采用锂空位模型阐述Mg:Fe:LiNbO₃晶体,吸收边和OH-吸收峰移动的机理.测试晶体的抗光致散射能力.Mg:(5 mol%)Fe:LiNbO₃晶体抗光致散射能力比Fe:LiNbO₃晶体提高一个数量级以上.测试晶体的衍射效率和响应时间.Mg:Fe:LiNbO₃晶体响应速度比Fe:LiNbO₃晶体提高四倍.     

稀磁半导体Zn1-xMnxTe吸收光谱压力红移的理论研究

以自由Mn²⁺离子的径向波函数为基础,通过引入电子云延伸效应系数κ来修正这一径向波函数,得到了稀磁半导体Zn_1-xMn_xTe晶体中Mn²⁺离子的径向波函数.以此波函数为基础,研究了Zn1-xMnxTe晶体吸收光谱的高压谱移特性,并且得到了吸收谱中四条谱线随压力的红移规律.     

微通道板空间光调制器中电光调制的传递特性

本文利用折射率椭球和点电荷模型研究了MSLM中偏z轴斛切LiNbO₃晶体的介电,电光传递过程。导出了在纵向,横向电场同时存在时电光效应的表达式及调制区的电荷——电压传递函数解析式。讨论了横向电场和器件结构参数对输出的影响及优化设计问题。指出偏z轴30°～60°切割晶体都可得到较好结果。     

态|ψ3(3)〉q广义电场分量的等幂次N次方H压缩

构造了由多模复共轭相干态|{iZ_j^*}〉_q、多模复共轭虚相干态|{iZ_j^*}〉_q(j=1,2,…q)和多模真空态|{0_j}〉_q线性叠加所组成的第Ⅲ类三态叠加多模叠加态光场|ψ₃⁽³⁾〉_q.利用多模压缩态理论,研究了态|ψ₃⁽³⁾〉_q中广义电场分量(即第二正交相位分量)的广义非线性等幂次N次方H压缩特性.发现:态|ψ₃⁽³⁾〉_q是一种典型的三态叠加多模非经典光场;当腔模总数q与压缩次数N之积q·N为偶数时,在一定条件下,态|ψ₃⁽³⁾〉_q的广义电场分量可分别呈现出周期性变化的广义非线性等幂次奇数模-偶数次、偶数模-奇数次、偶数模-偶数次N次方H压缩效应.     

利用BSO晶体的电控自聚焦效应实现的一种新型电光调制

BSO(硅酸铋)晶体除了具有热自聚焦效应外¹,还具有电控自聚焦效应²,基于电控自聚焦效应,又进一步对高斯光束经BSO晶体自聚焦后的远场光斑中心处的光强与加在晶体通光方向上的电压和入射光功率的关系进行了理论和实验研究,提出一种新的电光调制方法。理论与实验相符,进一步验证了文献1、2的结论.     

玻璃中CdSSe纳米晶体的光谱性能

对掺有镉、硒、硫的玻璃在650—800℃退火4?h，生长了不同尺寸的CdS0.13Se0.87纳米晶体，测量了纳米晶体的吸收光谱、光致发光（PL）谱和电调制光谱，确定了纳米晶体部分电子态的能量，讨论了CdSSe纳米晶体的光学性质与其尺寸之间的依赖关系.随着纳米晶体尺寸的增大，对应激子的吸收峰、PL峰及电吸收信号发生红移，表现出明显的量子尺寸效应.小尺寸纳米晶体的电吸收表现为量子受限的Stark效应，而大尺寸纳米晶体的电吸收线形与体材料的相似；随着纳米晶体尺寸的增大，电吸收信号增强.所有尺寸的纳米晶体都表现 关键词： CdSSe纳米晶体 吸收光谱 光致发光谱 电光响应     

Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron–hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron–hole interactions is observed with increasing external ZnS shell size. The strong electron–hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.     

Third-Order Nonlinear Optical Response near the Plasmon Resonance Band of Cu_(2-x)Se Nanocrystals

The third-order nonlinear optical properties of water-soluble Cu_(2-x)Se nanocrystals are studied in the near infrared range of 700-980 nm using a femtosecond pulsed laser by the Z-scan technique. It is observed that the nonlinear optical response of Cu_(2-x)Se nanocrystals is sensitively dependent on the excitation wavelength and exhibits the enhanced nonlinearity compared with other selenides such as ZnSe and CdSe. The W-shaped Z-scan trace, a mixture of the reversed saturated absorption and saturated absorption, is observed near the plasmon resonance band of Cu_(2-x)Se nanocrystals, which is attributed to the state-filling of free carriers generated by copper vacancies(self-doping effect) of Cu_(2-x)Se nanocrystals as well as the hot carrier thermal effect upon intense femtosecond laser excitation. The large nonlinear optical response and tunable plasmonic band make Cu_(2-x)Se nanocrystals promising materials for applications in ultra-fast all-optical switching devices as well as nonlinear nanosensors.     

Optical properties of cadmium sulfide nanocrystals obtained by the sol-gel method in gelatin

Based on analysis of optical absorption data for CdS nanocrystals obtained by sol-gel technology in gelatin, we have studied the effect of technological factors (reagent concentrations, gelatin concentration) on the growth process and size distribution of the synthesized nanocrystals. Depending on the reagent concentration, we synthesized CdS nanocrystals with mean radii in the range . We have shown that for a low gelatin content (1%), nanocrystals of different sizes are formed (1.7 nm and 2.6 nm). With an increase in the gelatin concentration, the size dispersion decreases and nanocrystals of a single mean radius (2.3 nm) are formed. We have established a correlation between the size dispersion and the shape of the photoluminescence spectrum of the CdS nanocrystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 556–562, July–August, 2008.     

Microemulsion-mediated synthesis of cadmium zinc sulfide nanocrystals with composition-modulated optical properties

Cadmium zinc sulfide nanocrystals were synthesized by a microemulsion-mediated process, which involving two steps: the preparation of CdS (or ZnS) seeds and the succedent hydrothermal growth of ZnS (or CdS) component. The XRD results show that the cadmium zinc sulfide nanocrystals with CdS seeds present a hexagonally homogeneous alloyed structure, while the ones with ZnS seeds mainly take on the characteristic of hexagonal CdS nanocrystals. The intrinsic factors influencing the crystal structures were discussed. The UV-vis and photoluminescence (PL) spectra indicate that the optical properties of the obtained nanocrystals with CdS seeds can be continuously modulated by tuning their compositions, although their sizes and size distributions are not under a strict control. The composition-modulated strategy, along with the hydrothermal microemulsion process, will be an effective route to achieve semiconductor nanocrystals with tunable optical properties under more manageable conditions.     

SELF-ASSEMBLY AND POLARIZABILITY OF CAPPED CdS NANOCRYSTALS ON SILICON SURFACES

The zinc-blende CdS nanocrystals with particle size less than 10nm were prepared in solution with a molecular surfactant. The particle surface was modified with capping molecules, bis(2-ethylhexyl) sulfosuccinate disodium salt (AOT) or hexametaphosphate (HMP). The colloid solution was deposited on silicon wafer and the assembly of these nanocrystals was studied by atomic force microscopy. It was found that the CdS/AOT formed a monolayer by simply dropping the colloid solution on silicon surface, while CdS/HMP exhibited 3D structure with prefered orientation in the similar deposition process. A dynamic electric force microscopy was performed and the polarizability was measured from the resonance of cantilever under applied alternating voltage between tip and substrate. The dielectric constant of CdS nanocrystal was estimated by comparing the different electric capacitance of Au and CdS nanocrystals.     

CdS/HgS/CdS球状纳米系统高能级斯塔克线度效应

研究了在层间作用和电场作用下球状纳米系统的电子能量和波函数.以CdS/HgS/CdS球状纳米系统为例,讨论了层间作用、电场和样品线度对高能级斯塔克效应以及谱线频率和强度的影响.结果表明：CdS/HgS/CdS球状纳米系统在外电场作用下发生斯塔克效应的能级分裂规律与氢原子类似,但能级位移量不同.谱线频移与电场强度的平方成正比,多数谱线的频移随线度增大而减小,少数谱线的频移则相反;而层间作用引起谱线的频移随线度增大而减小.除少数谱线外,多数谱线的相对强度随线度增大而减小,层间作用不会改变相对强度随线度的变化趋 关键词： CdS/HgS/CdS球状纳米系统 斯塔克效应 谱线频率 谱线强度     

Electromodulation spectroscopy of excitons: High field regime

The effects of electric field on excitons have been investigated experimentally by means of electroabsorption (EA). The behavior of excitons with ionization fields F_I of the same order of magnitude as or smaller than typical applied fields is reported. EA spectra associated with excitons in TlBr, PbI₂, BiI₃, trigonal Se, and α-monoclinic Se will illustrate this case. In this situation the EA signal arises principally from the effect on the exciton ground state, and no finer structure could be detected. The exciton ground state undergoes a shift to higher energies with the applied field. Characteristic dependences with field of the sizes, energy position of the peaks, and zero crossing points of the EA signals have been found. Estimates of exciton parameters can be readily obtained from the EA spectra. Unusual features of the exciton EA spectra PbI₂ are discussed. Qualitatively, at least, theoretical predictions are obeyed.     

纳米CdS-磺化聚苯胺（SPAn）多层复合膜的光学特性研究

研究了利用层-层自组织生长法制备的磺化聚苯胺-CdS纳米晶体复合膜的光学特性.研究发现，随样品中CdS 纳米晶体尺寸的减小，量子尺寸效应明显增强；在紫外吸收谱中表现为吸收边出现了明显蓝移；在光致发光谱中，不仅激子直接复合产生的带边发射产生了蓝移，而且陷阱态复合产生的宽带发射也发生了蓝移.还发现样品经低温退火处理后，激子复合产生的带边发射显著增强，发射带宽随纳米尺寸的减小而变窄.这说明退火后CdS 纳米晶粒的有序性和均匀度显著增加. 关键词： CdS 纳米晶体 SPAn 吸收 发光