Photoselection of impurity molecules with respect to the orientation of their stark moments induced by an amorphous matrix

A method of selective (relative to the magnitude of the linear Stark effect in zero-dipole impurity molecules) burning of holes in the spectra of amorphous matrices is studied. It is shown that this method makes it possible not only to select a subensemble of impurity molecules having both preset energy of the 0-0 transition and magnitude of the matrix-induced Stark moment, but also to divide this subensemble into two fractions whose Stark moments are predominantly oriented either along the transition moment or perpendicular to it. The possibility of experimental verification of the most popular hypothesis about the origin of induced Stark moments, which neglects a possible correlation between the direction of the Stark moment and that of the transition dipole moment, is considered. The method described also allows one to study experimentally the correlation of some other photophysical parameters of impurity molecules with the direction of local internal fields relative to the vector of the transition dipole moment.     

Electric dichroism of a multiwell spectral hole as an indicator of anisotropy in the distribution of stark moments of impurity molecules

Burning of multiwell holes in impurity-absorption spectra of glasses and polymers in an alternating electric field was theoretically studied. A case of circularly polarized burning radiation with a spectrum consisting of a series of close equidistant lines that shift synchronously with the variation of the electric field across the sample was considered. It was shown that an electric field applied to the sample after hole burning changes the optical density in the hole center, and that this change depends on the orientation of the plane of polarization of the probing radiation. Centrosymmetric impurity molecules, whose Stark moments (with randomly distributed magnitudes and directions) are governed only by their interaction with matrix molecules, and molecules with small intrinsic permanent Stark moments were considered. It was shown that the measurements of electric dichroism of a multiwell spectral hole make it possible to study both the anisotropy of matrix-induced moments and additional moments that arise, for example, when a metal atom leaves the plane of a metalloporphyrin molecule. It was also shown that the sensitivity and selectivity of the suggested method exceed those of known methods.     

Optical fractionation of an ensemble of impurity molecules over the magnitude of a Stark moment induced by an amorphous matrix

A method of selective (with respect to the Stark effect) burning of a spectral hole in the 0-0 absorption band of zero-dipole impurity molecules is suggested. It is shown that in combination with the Stark modulation of the optical density of a sample, this method makes it possible to determine that contribution to the total absorption and luminescence of the sample that the impurity molecules with a preset magnitude of the matrix-induced Stark moment (provided this magnitude exceeds the mean value for the entire ensemble) make. This allows one to experimentally study both the distribution of impurity molecules over the magnitude of the Stark moment and the correlation of the Stark moment with other parameters of impurity molecules.     

Photoselection of impurity centers in amorphous media over the hole-burning rate and the value of the induced Stark moment

It is shown that probing of the bottom of a multi-well spectral hole by frequency-modulated light allows one to study, in amorphous systems, the subensembles of impurity molecules, whose distribution over the hole-burning quantum yield and the matrix-induced Stark moment is different (narrower) from their initial distribution. This permits the study of correlation relations between these two distributions and between each of these distributions and other distributions.     

Hole burning spectroscopy with preliminary photoselection of impurity molecules

The photoselection of impurity molecules caused by spectral hole burning produces a specific spectral angular distribution of the molecules in low-temperature amorphous matrices: All the molecules, whose zero-phonon absorption lines lie within a selected narrow spectral interval, have a specified distribution of their orientations relative to the laboratory coordinate system. In this paper, the possibility of application of known methods of hole burning in this spectral interval is studied and the outlook for combination of these methods with preliminary photoselection is demonstrated by the example of the Stark effect.     

New manifestation of the statistical nature of orientation ordering in impure nematics

It is found that the splitting of polarized electron absorption bands of impurity dye molecules is inverted with temperature in a nematic liquid-crystal matrix. This effect is caused by the statistical nature of orientation ordering of impurity molecules and by the manifestation of higher order moments of the orientation distribution function.     

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.     

铯原子里德堡态Stark能量及电偶极矩的测量和理论计算

里德堡原子由于具有体积大、寿命长、易极化及在外电场中能级易于操控等特点, 已经成为了目前物理学领域研究的热点之一. 本文在磁光阱中实验测量了铯原子15P_3/2和16P_3/2态的Stark光谱,根据光谱给出了15P_3/2和16P_3/2|m|=1/2 Stark态在0-1400 V/cm场强范围适用的Stark 能量和偶极矩的经验性解析表达式; 用数值方法求解薛定谔方程获得了这些态的Stark能量、偶极矩和电子几率密度分布. 电子几率密度分布定性说明了计算的偶极矩矢量的方向是正确的. 计算的Stark能量、偶极矩与实验结果相一致.     

Electroreflectance vibrational spectroscopy: A new surface analysis technique using diode lasers

A new infrared technique to measure the vibrational spectra of adsorbed molecules is introduced. An Infrared active mode of an oriented molecule has a first order Stark effect. Therefore, infrared absorption by oriented adsorbed molecules is modulated by an alternating electric field. The spectra is obtained by measuring this using a diode laser. The advantages and limitations of Electroreflectance Vibrational Spectroscopy (EVS) are discussed. We calculate the Stark tuning rate and consequent signal amplitude for a number of diatomic molecules. Measurements of diode laser Intensity noise are used to estimate the signal to noise ratio for comparison with other techniques.     

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.     

Probing of the spectral diffusion in doped glasses by fluctuations of dichroism

A method of studying spectral diffusion using temporal fluctuations of the dichroism of an isotropic sample is described. Unlike conventional methods of absorption spectroscopy of single molecules, this method is easier to realize, provides direct information about the distribution of two-level systems over the relaxation rate, and does not require that the absorption lines be Stark modulated in frequency. The latter fact means that this method is applicable to conducting matrices (e.g., for studying current-induced relaxations in polymer materials). In combination with the probing of spectral diffusion using fluorescence intensity fluctuations, this method allows one to determine the degree of correlation between the distributions of impurity centers over the relaxation rate and over the fluorescence quantum yield.     

Dipole moments of molecules solvated in helium nanodroplets

Stark spectra are reported for hydrogen cyanide and cyanoacetylene solvated in helium nanodroplets. The goal of this study is to understand the influence of the helium solvent on measurements of the permanent electric dipole moment of a molecule. We find that the dipole moments of the helium solvated molecules, calculated assuming the electric field is the same as in vacuum, are slightly smaller than the well-known gas-phase dipole moments of HCN and HCCCN. A simple elliptical cavity model quantitatively accounts for this difference, which arises from the dipole-induced polarization of the helium.     

Pressure influence on the Stark effect of impurity states in a strained wurtzite GaN/AlxGa1-xN heterojunction

A variational method is adopted to investigate the properties of shallow impurity states near the interface in a free strained wurtzite GaN/AlxGa1-xN heterojunction under hydrostatic pressure and external electric field by using a simplified coherent potential approximation. Considering the biaxial strain due to lattice mismatch or epitaxial growth and the uniaxial strains effects, we investigated the Stark energy shift led by an external electric field for impurity states as functions of pressure as well as the impurity position, Al component and areal electron density. The numerical result shows that the binding energy near linearly increases with pressure from 0 to 10 GPa. It is also found that the binding energy as a function of the electric field perpendicular to the interface shows an un-linear red shift or a blue shift for different impurity positions. The effect of increasing x on blue shift is more significant than that on the red shift for the impurity in the channel near the interface. The pressure influence on the Stark shift is more obvious with increase of electric field and the distance between an impurity and the interface. The increase of pressure decreases the blue shift but increases the red shift.     

不同微场分布函数对Stark加宽和频移的影响

分别采用Holtsmark,Neutral Point,Nearest-Neighbor和Mayer模型微场分布函数对Stark线型进行了研究,进而得到相应微场函数下的Stark加宽和频移,研究了4种不同的微场分布函数对Stark加宽和频移的影响。研究结果表明,在电子加宽参数不变时,4种微场分布函数对Stark加宽和频移的影响随离子加宽参数的增加而增加;在离子加宽参数不变时,4种微场分布函数对Stark加宽和频移的影响随电子加宽参数的增加而增加;特别是,当离子加宽参数较大时,Mayer模型微场分布函数对Stark加宽和频移的影响异常明显。这说明,微场分布函数对谱线的加宽和频移的影响在离子与离子碰撞剧烈的等离子体环境中尤其显著, 在这样的等离子体环境中,进行等离子体诊断时,选择合适的微场分布函数非常重要。结果对等离子体诊断有一定参考价值。     

Observation of the linear stark effect in a single acceptor in Si

The Stark splitting of a single fourfold degenerate impurity located within the built-in potential of a metal-semiconductor contact is investigated using low temperature transport measurements. A model is developed and used to analyze transport as a function of temperature, bias voltage, and magnetic field. Our data is consistent with a boron impurity. We report g factors of g_{1/2}=1.14 and g_{3/2}=1.72 and a linear Stark splitting 2Delta of 0.1 meV.     

不同微场分布函数下的光谱线型

根据光谱学,总的光谱线型是各种加宽机制的卷积结果。考虑到等离子体中的离子碰撞,Stark加宽本质上是一种非对称的光谱线型, 其中微场分布函数对光谱线型起着非常关键的作用。该文利用不同的微场分布函数研究了微场分布函数对总的光谱线型的影响。研究结果表明,在电子加宽参数和离子加宽参数很小时,不同微场分布函数对整个光谱线型的影响基本相似,但随着离子加宽参数的增加,3种不同的微场分布函数对Stark光谱线型的影响逐渐增加; 随着电子加宽参数的增加,不同的微场分布函数对Stark光谱线型的影响也逐渐增加; 但总体上Holtsmark分布和Nearest-Neighbor场分布下的光谱线型差别较小,但是Mayer模型对光谱线型影响较大。特别是,当离子加宽参数较大时,Mayer模型对光谱线型的影响异常明显,这也正说明离子间碰撞剧烈时对光谱线型的影响很大。该结果对等离子体参数诊断有一定参考价值。     

Density of states of a disordered Hubbard model using the modified moments method

We apply the modified-moments method to compute the density of states of the impurity band of a doped semi-conductor in the intermediate region of impurity concentrations. This method is used to correct the density of states obtained by interpolating between the high and low concentration limit asymptotic expressions. The calculation is based on the Hubbard model in the atomic limit without spin ordering. The overlap integral is assumed to be a Gaussian function of the impurity separation. Use is made of the first seven moments of the exact distribution and of the low and high concentration limit approximations previously calculated. The first six moments are employed to determine the orthogonal polynomial expansion of the density of states while the seventh moment is used as a check on the accuracy of the distribution obtained. The results are similar to the previous ones using a truncated Edgeworth series for the correction term but the present method has the advantage of being a more systematic approach.     

Local magnetization of Co andMn impurities in the reentrant spin glass Au0.82Fe0.18

The low-temperature nuclear orientation technique has been used to study the magnetic behaviour of⁶⁰Co and⁵⁴Mn impurity atoms in the reentrant spin glass Au_0.82Fe_0.18. The results obtained for⁶⁰Co indicate that Co moments follow the distribution of Fe directions. In contrast, Mn moments show a spread directional distribution. These results are the consequence of the different character of Mn-Fe andFe-Fe interactions at short distances.     

Electric dipole moments of lithium atoms in Rydberg states

Recently, the diverse properties of Rydberg atoms, which probably arise from its large electric dipole moment(EDM),have been explored. In this paper, we report electric dipole moments along with Stark energies and charge densities of lithium Rydberg states in the presence of electric fields, calculated by matrix diagonalization. Huge electric dipole moments are discovered. In order to check the validity of the EDMs, we also use these electric dipole moments to calculate the Stark energies by numerical integration. The results agree with those calculated by matrix diagonalization.