γ-LiAlO2上a面ZnO薄膜的光谱特性研究

利用激光脉冲沉积(PLD)技术在(302)γ-LiAlO₂衬底上成功生长了非极性的a面(1120)ZnO薄膜,光致发光谱(PL)带边发射峰半峰宽仅为115meV.研究了非极性ZnO薄膜光谱特性的面内各向异性,发现随着入射光偏振方向改变,在偏振透射光谱上,吸收边移动了20meV,这与A、B激子和C激子的能量差一致;而在拉曼光谱上,激发光偏振方向的改变导致E₂模式的强度发生明显改变. 关键词： 非极性ZnO 2')" href="#">γ-LiAlO₂ PLD     

Yb:CaF2-SrF2激光晶体光谱性能以及热学性能的研究

采用坩埚下降法生长了Yb: CaF₂-SrF₂晶体,测试了该晶体的吸收和荧光光谱 以及在不同温度下晶体的热扩散系数和热膨胀系数,并且计算了晶体的热膨胀系数以及在常温下的热导率. 采用对比的方法,对晶体的吸收光谱,荧光光谱,热学性能进行了分析.从吸收和荧光光谱结果表明: 在掺杂相对较高浓度的SrF₂的混晶中, Yb³⁺吸收截面和发射截面比较大. Yb: CaF₂-SrF₂ (19%)晶体在1040 nm附近的发射截面比较大,光谱也比较宽. 这说明在掺杂相同浓度Yb时,混晶中CaF₂, SrF₂的比例不同,晶体的光谱性质不同, 主要原因是在混晶中晶体的无序度不同,晶体对称性降低,形成低对称光学中心. 从热扩散系数计算的热导率结果看出晶体具有比较好的热导率.     

Fluorescence anisotropy of cyanobacterial phycobilisomes oriented in polyvinyl alcohol (PVA) films

Polarized absorption (at 296 and 85 K), fluorescence, and photoacoustic (at 296 and 85 K) spectra of antenna complexes—phycobilisomes isolated from cyanobacteriaTolypothrix tenuis andOscillatoria and embedded in isotropic and anisotropic polyvinyl alcohol films—were measured. From the sets of polarized components of emission, the anisotropy of fluorescence for the pools of differently oriented molecules was calculated. On the basis of polarized photoacoustic and emission spectra, the competition between the process of thermal deactivation of excitation and excitation energy transfer in a chain of excitation donor and acceptor chromophores of phycobilisomes is discussed.     

Intraband absorption and emission of light in quantum wells and quantum dots

High-resolution spectroscopy in the mid-infrared spectral range is used to study electronic transitions between size-quantization subbands in stepped quantum wells under picosecond interband excitation. The contributions from intersubband and intrasubband absorption of light are separated by using the difference in time profiles of the absorption coefficient for these cases. For stepped quantum wells, spontaneous interband luminescence and superluminescence are studied for different excitation levels. For structures with quantum dots, the intraband absorption spectra for n-and p-type structures and the spectra of photoinduced intraband absorption and emission (for polarized radiation) for undoped structures are studied.     

Two-dimensional dye crystals with controllable optical properties

The structure, molecular ordering and optical properties of single crystals of cyanine dyes grown by adsorption from a water subphase to a positively charged lipid monolayer are discussed. These crystals are one monolayer thick, of uniform dimensions between 10 and 100μm (depending on nucleation conditions) and of rectangular shape. Single crystals were studied by transmission electron diffraction and by polarized absorption and emission spectroscopy.

We show that the crystals consist of two rows of densely stacked molecules with two different orientations of the long molecular axes. This leads to two perpendicularly polarized absorption bands. The measured splitting is in accordance with results of extended dipole calculations. The latter were performed for crystals of three slightly different molecules where the angles between the long axes varied between 70° and 100°. The aliphatic tails form a lattice which is epitaxially related to the centered rectangular one of the dyes. It is incommensurate, and the tails are tilted with tilt azimuth either parallel to the a or to the b axis (depending on the type of dye) of the dye lattice.

The procedure allows formation of mixed crystals with structural parameters, depending on composition, between those of the pure compounds. Hence also the optical spectra can be tuned via composition maintaining sharp band edges and emission bands.     

基于密度泛函的甲醇和乙醇荧光特性研究

使用英国爱丁堡FLS920P荧光光谱仪,对甲醇、乙醇的紫外吸收光谱和荧光光谱进行实验检测,得到二者的光谱特征参数。分别采用密度泛函理论(DFT)和单激发组态相互作用(CIS)对二者分子的基态和激发态结构进行优化,并比较两种分子在不同能态下的差异。应用含时密度泛函理论(TD-DFT)的不同泛函结合极化连续介质模型(PCM)在6-31++G(d, p)水平上分别计算了二者的紫外吸收光谱和荧光光谱,与实验结果吻合。分析了甲醇、乙醇荧光产生机理,同时分析了不同泛函对于计算光谱的影响。结果表明：甲醇、乙醇在紫外波段有微弱吸收,在紫外激发下能产生拉曼峰和微弱的荧光峰。甲醇、乙醇的吸收光谱是由里德堡激发产生,产生荧光的轨道跃迁为σ*→π*。泛函OLYP能够较好地重现实验吸收能,而泛函MPWK能够较好地重现实验发射能,并且发现不同的纯泛函计算跃迁能也具有差异性。结果可为醇类分子的分子特性研究提供参考。     

Photo-physical properties and quantum yield of some laser dyes in new polymer host

The field of laser dyes-active solid polymer materials is a promising field and quite competitive with liquid dye lasers. This paper investigates some photo-physical parameters of pyromethene (PM-567, PM-597) and Rhodamine B dyes incorporated into glycidyl methacrylate (GMA) promising polymeric host matrix. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to FT-Raman spectra as an indication for binding the dye molecules with the backbones of GMA polymeric chain.     

Growth studies of m-GaN layers on LiAlO2 by MOCVD

This paper reports that the m-plane GaN layer is grown on （200）-plane LiAlO2 substrate by metal-organic chemical wpour deposition （MOCVD） method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer＇s thickness. The high transmittance （80%）, sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate.     

Spectroscopic study of a representative polar cap of buckminsterfullerene: Cyclopentacorannulene

The spectroscopic properties of corannulene and cyclopentacorannulene are examined by use of absorption and steady-state fluorescence measurements. A red shift in the emission maxima of cyclopentacorannulene is noted with respect to the emission maxima in the corannulene spectrum. Similar differences in the absorption spectra of both molecules are also observed. Reasons for the dissimilarities in the absorption and emission spectra of these molecules are discussed. The fluorescence quantum yields and lifetimes of the molecules measured in organic solvents are reported. The fluorescence quantum yield and lifetime of cyclopentacorannulene are lower than those of corannulene. This difference is attributed to the highly strained and nonplanar structure of cyclopentacorannulene. The effectiveness of nitromethane as a quencher of corannulene and cyclopentacorannulene fluorescence is examined. In contrast to previously reported results, the fluorescence of these molecules is quenched by nitromethane. Fluorescence quenching of the molecules has been attributed to complex formation in the ground state, i.e., static quenching.     

Spectral features of impurity luminescence in uniaxial polymer films and nematic glasses

A study is conducted of the static shift and the splitting of the photoluminescence and electroluminescence polarized bands of uniaxial impurity molecules, embedded into uniaxial polymer films with axial or in-plane orientation of the impurity subsystem or into the vitreous phase of a nematic liquid crystal. Dependences of the band shift and the splitting on the type of alignment of impurity molecules, the polarization of transition moments in absorption and emission, and the host-impurity anisotropic interactions of different ranks are established. For both types of host matrices, characteristic features of orientational statistics of impurity molecules at a high degree of orientation ordering are studied. These features are revealed in a qualitative difference between the dependences of positions and splittings of polarized impurity fluorescence bands on the order parameter of the impurity molecules axially ordered in stretched polymer films and relevant dependences in nematic glasses. Specific features of the polarized impurity-related photoluminescence and electroluminescence in the matrices under study, observed experimentally, are interpreted.     

不同初始振动态下D2O在B带的态-态光解动力学

利用高精度的非绝热从头算势能面,采用量子实波包方法研究了D₂O在3个不同初始振动态(0,1,0)、(1,0,0)和(0,0,1)下光激发到~B态解离过程的态-态量子动力学．结果表明,由于初始振动波函数的形状不同,从不同振动态产生的吸收光谱、产物分布和产物分支比具有不同的动力学特性．弯曲振动态(010)的吸收谱呈现出两波瓣的形状且中间具有较浅的极小值,其基态产物OD( ~X)在高能量区域会出现轻微的振动态反转现象．所有初始振动态得到的激发态产物OD(_?)的振-转态分布都随能量的变化出现强烈的震荡,这是由于受到了激发态势能面上长寿命共振态的影响．反对称伸缩振动态(0,0,1)在高能量区域具有较大的产物分支比OD(_?)/OD( ~X),表明绝热通道在某些情形下是主要的解离通道．     

等离子体X射线吸收谱及发射谱研究

 报道计算高温高密等离子体吸收谱和发射谱（光学薄）的理论方法；该方法基于相对论原子理论，可以计算任何单元素以及多元素等离子体的谱分辨X射线吸收谱和发射谱（光学薄）；应用了量子亏损理论，可以减少计算量。利用该方法计算金等离子体LTE吸收谱，计算结果与实验符合良好。本文还对金等离子体LTE的光学薄发射谱进行了研究, 这将有利于对实验进行进一步的诊断分析。该理论计算方法还可提供等离子体内各电离度能级布居等重要物理参数。因此经“标准实验”检验的该理论计算方法将是提供ICF“精密”物理辐射参数的重要基础。     

钨酸铅晶体中与铅空位有关的电子结构和色心模型研究

根据密度泛函理论对钨酸铅晶体中铅空位周围的晶格进行了结构优化，计算得到铅空位周围的晶格结构、电子态密度分布和偏振吸收光谱；计算结果表明钨酸铅晶体中铅空位的两价负电性是通过铅空位周围的氧共同抓获两个空穴来维持局部电中性的，即铅空位周围形成的色心模型为［O₂^3--V_Pb^2--O₂^3-］，不同的氧离子抓获空穴方式不同形成不同的色心，对应不同的吸收带；根据吸收带的偏振性质，提出了各个 关键词： 钨酸铅晶体 色心模型 电子结构 偏振特性     

Optical properties of Pr3+-doped SrWO4 crystal

The polarized absorption and emission spectra of Pr³⁺ ions in SrWO₄ single crystals were investigated at room temperature. The standard and modified Judd–Ofelt theories have been applied to analyze the polarized absorption spectra to determine the spectroscopic parameters, including the Judd–Ofelt intensity parameters Ω_t (t=2,4,6), radiative transition probabilities, radiative lifetimes and branching ratios. The stimulated emission cross sections and fluorescence lifetimes of the promising laser level were obtained. PACS 78.55.Hx; 42.70.Hj; 78.20.-e     

Photophysical characterization of pyrromethene 597 laser dye in silicon-containing organic matrices

Samples of dipyrromethene-BF₂ dye PM597 incorporated in copolymers of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) with methyl methacrylate (MMA) and 2-hydroxyethylmethacrylate (HEMA), and in terpolymers of MMA, HEMA and TMSPMA are characterized. The absorption cross-section spectra, stimulated emission cross-section spectra, and the excited-state absorption cross-section at 527 nm are determined. The fluorescence quantum distributions and fluorescence lifetimes are measured. The photo-degradation is studied under cw laser excitation conditions and quantum yields of photo-degradation are extracted. PM597 solid state samples are compared with PM597 in liquid ethyl acetate solution. The fluorescence quantum yield of PM597 is higher in doped samples (around 70%) compared to PM597 in ethyl acetate (43%). The excited-state absorption cross-section was found to be negligibly small. The photo-stability is considerably larger in the polymeric samples compared to the liquid solutions. PACS 42.55.-f; 78.45.+h; 78.55.-m; 78.40.Me     

凝聚相中叶绿素A荧光偏振光谱线型分析

本文报导了用氩离子激光器488nm线偏振光激发时叶绿素A(Chla)己烷溶液在12.5K下偏振荧光的实验结果。在波数为11200～20000cm-1范围内得到了完整的偏振荧光数据,并用计算机对仪器响应进行了校正。若把Chla单体、二聚体和齐聚体均视为荧光性杂质中心,则多中心荧光偏振度公式可写成:P(λ)= 。用该公式进行了数值模拟计算,得到几种典型的P(λ)谱图,发现每一个高斯分量Ii同P(λ)函数的一个峰,谷或肩呈现明显的对应关系。据此对chla的荧光偏振光谱的线型进行了分析和讨论。Chla单体、二聚体和齐聚体的不同激发态的荧光发射分量,均表现为Pλ曲线上的峰、谷或肩。实验结果与数值模拟计算预期的线型完全一致。     

Manifestations of the higher moments of the orientation distribution function of molecules in the spectral properties of an impurity nematic

The polarized electronic absorption spectra, orientation ordering, and the special local field features were studied for push-pull linear dye molecules with strong donor-acceptor electronic conjugation of terminal fragments in the matrix of a nematic liquid crystal. The temperature-induced inversion of the sign of the splitting of polarized impurity absorption bands was observed. This effect was shown to be caused by the statistical character of orientation ordering of impurity molecules and manifestation of the higher moments of the orientation distribution function. The dependence of local field parameters (Lorentz tensor components) of impurity molecules on their orientation ordering was established. This dependence was used to reproduce the temperature dependence of the orientation order parameter of the matrix.     

Ultrafast photoionization of ions and molecules by orthogonally polarized intense laser pulses: Effects of the time delay

We present the photoelectron momentum distributions(PMDs) and the photoelectron angular distributions(PADs) of He+ ions, aligned H2+ molecules and N2 molecules by intense orthogonally polarized laser pulses. Simulations are performed by numerically solving the corresponding two-dimensional time-dependent Schr?dinger equations(TDSEs) within the single-electron approximation frame. Photoelectron momentum distributions and photoelectron angular distributions present different patterns with the time delays Td, illustrating the dependences of the PMDs and PADs on the time delays by orthogonally polarized laser pulses. The evolution of the electron wavepackets can be employed to describe the intensity of the PADs from the TDSE simulations for N2 molecules.     

Blue luminescence in Tm-doped KGd(WO4)2 single crystals

Up-conversion blue emissions of trivalent thulium ions in monoclinic KGd(WO₄)₂ single crystals at 454 and 479 nm are reported for a single pump laser source at 688 nm. We grew thulium-doped KGd(WO₄)₂ single crystals at several concentrations from 0.1% to 10%. We recorded a polarized optical absorption spectrum for the ³F₂+³F₃ energy levels of thulium at room temperature and low temperature (6 K). From the low temperature emission spectra we determined the splitting of the ³H₆ ground state. The blue emissions are characterized as a function of the dopant concentration and temperature from 10 K to room temperature. To our knowledge, this is the first time that sequential two-photon excitation process (STEP) generated blue emissions in thulium-doped single crystals with a single excitation wavelength.     

Efficient two-dimensional atom localization in a five-level conductive chiral atomic medium via birefringence beam absorption spectrum

We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging.