CaWO4晶体中F型色心电子结构的研究

运用相对论的密度泛函离散变分法(DV-Xa)研究了CaWO4晶体中F型色心的电子结构.计算结果表明,F和F+心在禁带中引入了新的施主能级;分析了晶体内可能存在的光学跃迁模式,并通过过渡态的方法计算了F,F+心跃迁到导带底的能量分别为1.92 eV和2.42 eV.因此,从理论上推断了F和F+心在CaWO4晶体中可能引起650nm和515 nm的吸收,由此说明CaWO4晶体中650 nm和515 nm吸收带起源于晶体中的F和F+心.     

纳米ZnO和ZnO-SiO2复合薄膜的光学性质研究

通过溶胶凝胶(sol-gel)法分别在玻璃衬底上制备了ZnO纳米薄膜和ZnO-SiO₂纳米复合薄膜,并利用紫外-可见光分光光度计对薄膜的光学性能进行了分析.可见光-紫外透射谱显示,随着ZnO溶胶浓度从0.7mol/L降低到0.006mol/L,制备的ZnO薄膜从只出现一个380nm(对应的光学禁带宽度为3.27eV)左右的吸收边到在380和320nm(对应的光学禁带宽度为3.76eV)左右各出现一个吸收边,并且随着ZnO溶胶浓度的降低,在380—320nm波段内的透过率明显提高.而Z 关键词： 纳米ZnO 2复合薄膜')" href="#">ZnO-SiO₂复合薄膜 溶胶凝胶法 透射率     

CdSe/HgSe/CdSe量子点量子阱(QDQW)晶粒的光学性质和电子结构

以CdSe纳米晶体为核,用胶体化学的方法,通过化学替代反应,获得了不同阱层或不同垒层的CdSeHgSeCdSe量子点量子阱(QDQW)晶体.紫外可见光吸收谱研究表明,通过调节QDQW中间HgSe阱层的厚度从0.9nm至0,可以调节QDQW颗粒的带隙从1.8变化至2.1eV,实现QDQW纳米晶体的剪裁.光致荧光(PL)谱研究显示,QDQW形成后,CdSeHgSe纳米颗粒表面态得到钝化,显现出发光强度加强的带边荧光峰.利用有效质量近似模型,对QDQW晶粒内部电子的1s—1s态进行了估算,估算结果总体趋势与实验数据相符 关键词： 量子点量子阱晶体 能带剪裁 加强的带边荧光峰     

纳米ZnO和ZnO-SiO2复合薄膜的光学性质研究

通过溶胶凝胶(sol-gel)法分别在玻璃衬底上制备了ZnO纳米薄膜和ZnO-SiO2纳米复合薄膜,并利用紫外.可见光分光光度计对薄膜的光学性能进行了分析.可见光一紫外透射谱显示,随着Zn0溶胶浓度从0.7 mol/L降低到0.006 mol/L,制备的ZnO薄膜从只出现一个380 nm(对应的光学禁带宽度为3.27 eV)左右的吸收边到在380和320nm(对应的光学禁带宽度为3.76 ev)左右各出现一个吸收边,并且随着ZnO溶胶浓度的降低,在380-320 nm波段内的透过率明显提高.而ZnO-SiO2复合薄膜只在310 nm左右出现一个吸收边.SiOO2的包覆宽化了ZnO的禁带宽度,包覆后的禁带宽度可达到3.87 ev.     

含色心BaMgF4晶体电子结构的研究

运用相对论性的密度泛函离散变分法(DV-X)研究BaMgF4晶体中F型色心的电子结构.计算中采用冻结原子核的H原子模拟F心,在DV-Xα源程序增加H原子2p态,使F心激发态的计算结果在物理上更加合理.计算结果表明,F心的基态和激发态均出现在禁带中;并用过渡态的方法计算得到F心的电子从基态到激发态的光学跃迁能量为5.12eV,对应242nm处的吸收带,计算结果与实验结果吻合得很好,因此,推测F心在BaMgF4晶体中引起236～274 nm的吸收.     

基于黑色层纳米薄膜的可重构可见光滤波器

基于铁电材料的介电可调特性,提出一种新颖的基于黑色层纳米薄膜的可重构可见光滤波器,并比较了它与一维光子晶体滤波器反射光谱的可重构特性.实验结果表明,利用黑色层吸收非相干散射光可显著提高反射颜色对比度.当钛酸钡(BTO)薄膜的厚度从100 nm变为140 nm时,反射光谱的峰值波长由383.7 nm移动至501.2 nm,纳米薄膜的反射颜色从紫色变为蓝绿色.反射光谱的测试结果与有限元的模拟结果一致性良好.计算结果表明,当BTO薄膜的厚度为170 nm时,在21.8V直流驱动电压下,其折射率由2.4变化至2.0,反射峰值波长由595.3 nm移动至513.9 nm.     

纳米硅上的弯曲表面效应及其特征发光

纳米硅结构使能带的带隙展宽,并形成准直接能带带隙结构.弯曲表面上的某些键合可以在带隙中产生局域电子态,计算表明:纳米硅弯曲表面上的Si-N,Si=O和Si-O-Si键合能够分别在带隙中2.02 eV,1.78 eV和2.03 eV附近形成局域态子带,对应了实验光致荧光谱(PL)中605 nm处的LN线、693 nm处的LO1线和604 nm处的LO2线特征发光.特别是,Si-Yb键合在纳米硅弯曲表面上可以将发光波长调控到光通信窗口,在1310 nm到1600 nm范围形成LYb线特征发光.     

锗硅量子阱结构带间吸收边研究

利用光电流谱的方法对锗硅量子阱结构的带间吸收边进行了研究.实验观察到了在不同的偏压和温度下,锗硅量子阱结构的带间吸收边谱线发生了有规律的变化.通过对锗硅量子阱材料的光电流谱的带间跃迁吸收边的拟合,得到了硅导带到锗价带的能带宽度分别为1.043 eV和1.050 eV.随着外加电场的增强,带边的吸收曲线向低能方向移动.通过理论计算得到了带间跃迁吸收边的漂移量与外加电场的关系,并与实验吻合较好.随着温度的降低,带间吸收边向高能方向偏移,对于这一现象给出了定性的解释,并通过拟合得到了禁带宽度随温度的变化率.     

CaWO4晶体中F型色心电子结构的研究

运用相对论的密度泛函离散变分法(DV-Xα)研究了CaWO₄晶体中F型色心的电子结构. 计算结果表明，F和F⁺心在禁带中引入了新的施主能级；分析了晶体内可能存在的光学跃迁模式，并通过过渡态的方法计算了F，F⁺心跃迁到导带底的能量分别为1.92eV和2.42eV. 因此，从理论上推断了F和F⁺心在CaWO₄晶体中可能引起650nm和515nm的吸收，由此说明CaWO₄晶体中650nm和515nm吸收带起源于晶体中的F和F⁺心. 关键词： 4晶体')" href="#">CaWO₄晶体 +心')" href="#">F和F⁺心 DV-Xα     

偏硼酸钡晶体倍频系数和紫外吸收边的计算

偏硼酸钡(β-BaB_2O_4)晶体是我国首创的一种新型非线性光学晶体。实验表明它的透光波段为190～3000nm,宏观倍频系数x_(111)~(2ω)=4.6×10~(-9)e.s.u。CNDO/S计算能得到较好的x_(111)~(2ω)值但紫外吸收边竟达90nm,离实验值太远。本文从芳香环的EHMO理论出发,比较了几种无机芳香环和有机芳香环的单电子能谱,得到β-BaB_2O_4晶体的紫外吸收边和倍频系数值,跟实验值非常符合。针对紫外吸收边的争议,我们还用精度较高的SCF-X_a-SW方法计算了该晶体的电子能谱,结果支持上述的EHMO计算。本文最后简单讨论了影响非线性晶体紫外吸收边和倍频系数的因素。     

GaAs/SiO2纳米晶镶嵌薄膜的拉曼光谱与吸收光谱研究

采用射频磁控共溅射与高真空退火相结合的方法,分别在单晶硅片和光学石英玻璃片上制备了ＧａＡｓ／ＳｉＯ２纳米晶镶嵌薄膜样品。激光拉曼光谱的测量结果表明,退火态样品（４００℃,６０ｍｉｎ）的拉曼光谱特征峰呈现宽化和红移,红移量为９．５ｃｍ＾－１,对应薄膜中ＧａＡｓ纳米晶粒平均粒径约为３ｎｍ。样品的室浊吸收光谱测量结果表明,由于受量子限域效应的主导作用,与ＧａＡｓ块状单晶相比,样品光学吸收边呈现出明显的蓝     

X‐ray absorption near‐edge structure anomalous behaviour in structures with buried layers containing silicon nanocrystals

Substructure and phase composition of silicon suboxide films containing silicon nanocrystals and implanted with carbon have been investigated by means of the X‐ray absorption near‐edge structure technique with the use of synchrotron radiation. It is shown that formation of silicon nanocrystals in the films' depth (more than 60 nm) and their following transformation into silicon carbide nanocrystals leads to abnormal behaviour of the X‐ray absorption spectra in the elementary silicon absorption‐edge energy region (100–104 eV) or in the silicon oxide absorption‐edge energy region (104–110 eV). This abnormal behaviour is connected to X‐ray elastic backscattering on silicon or silicon carbide nanocrystals located in the silicon oxide films depth.     

Quantum confinement in germanium nanocrystal thin films

Thin films of semiconductor nanocrystals with tunable optical properties are promising materials for new device applications, but progress has been slow for group IV materials. We report absorption measurements near the absorption edge of thin films of germanium nanocrystals synthesized in a plasma and impacted onto substrates. Band gaps extracted from the absorption data vary from the near‐bulk value of 0.73 eV for 9.0 nm nanocrystals to over 1.0 eV for 4.7 nm nanocrystals. These values are comparable to those reported for isolated, non‐interacting germanium nanocrystals, indicating minimal loss of quantum confinement upon dense film formation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CdSe/CdS核/壳型纳米晶的光谱特性

以巯基乙酸为稳定剂制备了CdSe/CdS核／壳型纳米晶。用光吸收谱（Abs)、光致发光谱（PL）及光致发光激发谱（PLE）研究了CdS壳层对CdSe纳米晶电子结构，从而对其吸收和发光性能的影响。根据PL和PLE的结果以及带边激子精细结构的计算结果，我们用尺寸很小的纳米晶中所形成的基激缔合物解释了PL光谱与吸收边之间较大的Stokes位移。     

CdTe aggregates in KBr crystalline matrix

In this work, we report the experimental results on the fabrication and optical characterization of Czochralski (Cz) grown KBr single crystals doped with CdTe crystallites. The results of the optical absorption have shown two bands, the first one located at 250 nm demonstrates the incorporation of cadmium atoms in the KBr host followed by a partial chemical decomposition of CdTe, the second band located at 585 nm shows an optical response of CdTe aggregates. Photoluminescence spectra at room temperature before annealing showed a band located at 520 nm (2.38 eV), with a blue shift from the bulk gap of 0.82 eV (E_g (CdTe)=1.56 eV). While the photoluminescence spectra after annealing at 600 °C showed a band situated at 640 nm (1.93 eV), these bands are due to band-to-band transitions of CdTe nanocrystals with a blue shift from the bulk gap at 0.38 eV. Blue shift in optical absorption and photoluminescence spectra confirm nanometric size of dopant. X-ray diffraction (XRD) spectra have shown the incorporation of CdTe aggregates in KBr.     

Energy-filtered TEM imaging and EELS study of ODS particles and argon-filled cavities in ferritic-martensitic steels

Oxide-dispersion-strengthened (ODS) ferritic-martensitic steels with yttrium oxide (Y(2)O(3)) have been produced by mechanical alloying and hot isostatic pressing for use as advanced material in fusion power reactors. Argon gas, usually widely used as inert gas during mechanical alloying, was surprisingly detected in the nanodispersion-strengthened materials. Energy-filtered transmission electron microscopy (EFTEM) and electron energy loss spectroscopy (EELS) led to the following results: (i) chemical composition of ODS particles, (ii) voids with typical diameters of 1-6 nm are formed in the matrix, (iii) these voids are filled with Ar gas, and (iv) the high-density nanosized ODS particles serve as trapping centers for the Ar bubbles. The Ar L(3,2) energy loss edge at 245 eV as well as the absorption features of the ODS particle elements were identified in the EELS spectrum. The energy resolution in the EEL spectrum of about 1.0 eV allows to identify the electronic structure of the ODS particles.     

Growth and characteristics of lead sulfide nanocrystals produced by the porous alumina membrane

Lead sulfide (PbS) nanocrystals were formed by using Pb nanowires reacted with hydrogen sulfide (H₂S) gas. The structure and composition of the as-prepared nanocrystals were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscope and energy dispersive X-ray spectroscopy. According to the differential scanning calorimeter analysis, the PbS nanocrystals in a cubic structure owned excellent thermal stability. Furthermore, the optical properties including photoluminescence (PL) and Raman scatting spectrum were also measured. The PL emission measurement of the PbS nanocrystal showed that there was an orange-red emission peak located around 655 nm. A significant quantum confinement effect made the energy gap of PbS produce a blue shift from 0.41 eV to 1.9 eV.     

Electronic and optical properties of CdS/CdZnS nanocrystals

Cd1-x ZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn.The texture,structural transformation and optical properties with increasing x value in Cd1-x ZnxS are studied with scanning electron microscopy,electron diffraction patterning,and absorption spectra respectively.Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically.Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed,with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations,and thereby the interband emission energy is calculated as a function of the dot radius.The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically.Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm.The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content.The lattice constant gradually decreases as the Zn content increases.The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases.The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film.Our numerical results are in good agreement with the experimental results.     

Y2O2S:Eu nanocrystals, a strong quantum-confined luminescent system

Trivalent europium-doped yttrium oxysulfide nanocrystals synthesized using sol-gel thermolysis show significant blue shifts in the excitation bands corresponding to fundamental absorption, charge-transfer absorption. A significant blue shift observed in the fundamental absorption edge for the nanocrystals having an average crystallite size (φ) in the range 9-15 nm indicates a strong quantum confinement with a Bohr exciton radius of 5-13 nm. Also, the diffuse reflectance spectra and the corresponding Kubelka-Munk plot indicate the possibility of profound decrease in the absorption coefficient of Eu³⁺-ligand charge-transfer species necessitating further studies in this wide-gap semiconductor nanocrystalline system.