非掺杂GaN的黄光发射模型确定

提出了一种新的光谱———吸收归一化光致发光激发谱,并用这种光谱研究了非掺杂GaN的黄光发射.实验上首次直接测量出了黄光发射的初始态的共振吸收峰位,从而解决了长期争论的有关黄光发射的发光模型问题 关键词： GaN薄膜 黄光发射 吸收归一化光致发光激发谱     

GaP中1.71eV发光带的研究

本文研究了GaP中普遍出现的1.71eV光致发光(PL)宽带。这是一个与多个杂质能级有关的发光带,由吸收谱和光致发光激发谱(PLE)检测到在价带上方0.37—0.089eV范围内与该发光带有关的深能级。时间分辨谱测量表明。随着衰减过程的延续,谱峰移向低能方向,说明该带起源于D—A对复合。讨论了该发光带与背景Cu杂质有关的可能性及其发光机制和激发途径。     

GaN薄膜的蓝光和红光发射机理研究

由于生长工艺的不完善，非掺杂GaN薄膜中通常存在未知的杂质和缺陷，产生与这些未知杂质和缺陷能级相关的发光。报道了非掺杂GaN薄膜的692nm红色发光．并研究了非掺杂GaN薄膜的蓝、红色发光的发射机理；利用作者提出的吸收归一化光致发光激发光谱，直接测量出了非掺杂GaN薄膜的蓝、红色发光的初始态能级，确定蓝色发光为施主-价带跃迁复合，而红色发光为施主-受主跃迁复合；给出了黄、蓝、红光的发射模型。所取得的结果对于确定未知杂质和缺陷的种类具有重要的参考价值。     

玻璃中CdSeS纳米晶体的室温光致发光谱

对掺有过饱和的镉、硒和少量硫的玻璃在500～800℃分别退火4h,生长了不同尺寸的CdSe_1-xS_x纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300～800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600～650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。     

二氧化钛胶体及其自组装薄膜的光谱分析

水解钛酸四丁酯制备了二氧化钛胶体;采用静电自组装技术制备了聚电解质与二氧化钛胶体的复合薄膜;采用吸收光谱和荧光光谱对二氧化钛胶体及其复合薄膜进行了表征。吸收光谱显示,胶体的吸收带边蓝移,显示出量子尺寸效应,胶体的荧光光谱出现了多个发光带,最短发光波长位于371nm,发光主要集中在蓝光区域内;在252nm光源激发下。复合薄膜的发射谱带具有二氧化钛水溶胶的发射谱带的特征,荧光发射主要来源于二氧化钛,聚电解质的引入对复合薄膜的光致发光特性有一定影响。     

蓝宝石表面处理对氮化镓光学性质的影响

采用化学方法腐蚀部分c面蓝宝石衬底,在腐蚀区域形成一定的图案,利用LP-MOCVD在经过表面处理的蓝宝石衬底上外延生长GaN薄膜.利用GaN薄膜光学透射谱,结合椭偏测量得到的折射率色散公式,计算得到GaN薄膜厚度,与椭偏光谱结果几乎一致;在经过表面处理的蓝宝石衬底上外延生长的GaN薄膜表现出更优异的光学质量和结晶质量,其透射谱具有更高的透射率和更大的调制深度,而且其光致发光谱中的黄光带几乎可以忽略.     

纳米ZnO薄膜可见发射机制研究

利用溶胶－凝胶法 （Sol-Gel）制备了纳米ZnO薄膜，获得了高强的近紫外发射室温下测量了样品的光致发光谱(PL )、吸收谱(ABS)、X射线衍射谱(XRD).X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶态，具有六角纤锌矿结构和良好的C轴取向；发现随退火温度升高，（002）衍射峰强度显著增强，衍射峰的半高宽（FWHM）减小、纳米颗粒的粒径增大.由吸收谱(ABS)给出了样品室温下带隙宽度为3.30 eV.在PL谱中观察到二个荧光发射带，一个是中心波长位于392 nm附近强而尖的紫带，另一个是519 nm附近弱而宽的绿带研究了不同退火温度样品的光致发光峰值强度的变化关系，发现随退火温度升高，紫带峰值强度增强、绿带峰值强度减弱，均近似呈线性变化.证实了纳米ZnO薄膜绿光发射主要来自氧空位(Vo)形成的浅施主能级与锌空位(VZn)形成的浅受主能级之间的复合，或氧空位(Vo)形成的深施主能级上的电子至价带顶的跃迁；紫带来自于导带中的电子与价带中的空位形成的激子复合.     

热退火对Mn离子注入非故意掺杂GaN微结构、光学及磁学特性的影响

通过Mn离子注入非故意掺杂GaN外延层制备了GaN:Mn薄膜,并研究了退火温度对GaN:Mn薄膜的微结构、光学及磁学特性的影响.对不同退火温度处理后的GaN:Mn薄膜的拉曼谱测试显示,出现了由与离子注入相关的缺陷的局域振动(LV)和(Ga,Mn)N中Mn离子的LV引起的新的声子模.在GaN:Mn薄膜的光致发光谱中观察到位于2.16,2.53和2.92 eV处的三个新发光峰(带),其中位于2.16 eV处的新发光带不能排除来自Mn相关辐射复合的贡献.对GaN:Mn薄膜的霍尔测试显示,退火处理后样品表现出n型体材料特征.对GaN:Mn薄膜的振动样品磁强计测试显示,GaN:Mn薄膜具有室温铁磁性,其强弱受Mn相关杂质带中参与调节磁相互作用的空穴浓度的影响.     

溶胶-凝胶法制备ZnO薄膜及其光致发光性质

利用溶胶-凝胶法在石英衬底上制备了ZnO薄膜,通过测量样品的透射谱、X射线衍射谱、扫描电子显微镜(SEM)图像和光致发光谱研究了其结构特征和发光性质.结果表明:在衍射角2θ=34.32°处出现了对应(002)晶面的强衍射峰,ZnO膜呈多晶状态,具有六角纤矿晶体结构和良好的C轴择优取向,薄膜中颗粒的平均粒径为56nm;光致发光呈多发光峰状,有中心波长为378nm的紫带,520nm绿带,446nm附近的蓝带以及发现未见报道过的绿带以后中心波长为586nm和570nm两个弱发射峰.实验结果表明,制备的ZnO薄膜具有发光特性,但内部与深能级发射相关的结构缺陷浓度还是较高,样品中两个低能量光致发光应来源于晶粒间界的缺陷能级,多缺陷能级导致了多发射峰的光致发光谱.     

掺铜及掺铝多孔硅的光致发光及其发光机理

分别将特定杂质铜和铝引入多孔硅后，观察到了杂质铜和铝所引起的附加发光带：对于没有掺铜的多孔硅，其光致发光谱只有一个发光带；而掺过铜的多孔硅，其光致发光谱出现两个发光带，其中能量较低的发光带随主发光带而变化。在掺铝多孔硅的光致发光谱中，则出现4个与铝杂质能级有关发光带。我们认为上述与杂质有关的发光带是由截流子在杂质深能级上复合所致。     

Soft X-ray transition matrix elements: The role of approximation of the valence states

The coordinate, momentum and potential forms of the interband transitions matrix elements are equivalent when the initial and the final states are exactly known. For the soft X-ray transitions we assume exact core states, and approximate valence states. Then the three different forms of the matrix elements are no longer equivalent and are related by new, more general expressions. From these the qualitative conclusions regarding the appropriate form of the approximated valence states are derived. It turns out, that the orthogonalization of the approximate valence wave function to the core states is very important for the correct behaviour of the photon energy dependence of the soft X-ray emission. These results are illustrated by simple numerical examples.     

Polarization dependence of emission spectra of multiexcitons in self-assembled quantum dots

We have investigated the polarization dependence of the emission spectra of p-shell multiexcitons of a quantum dot when the single particle level spacing is larger than the characteristic energy of the Coulomb interactions. We find that there are many degenerate multiexciton states. The emission intensities depend on the number of degenerate initial and final states of the optical transitions. However, unlike the transition energies, they are essentially independent of the strength of the Coulomb interactions. In the presence of electron-hole symmetry the independence is exact.     

The origins of satellite lines in the LMM auger spectrum of copper

The vacancy satellite lines in the Cu LMM spectrum which originate from transitions between two hole initial states and three hole final states have been experimentally identified by changing the energy of the exciting x-rays from 1254eV to 950eV and so reducing the number of two hole initial states populated by L₁L₃M and L₂L₃M_4,5 Coster-Kronig transitions relative to the number of single L₃ holes.     

Theoretical investigation of electronic and optical properties of andalusite within density functional theory

The electronic and optical properties of andalusite were studied by using quantum-mechanical calculations based on the density functional theory (DFT). The electronic structure shows that andalusite has a direct band gap of 5.01 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of andalusite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s states play a major role in optical transitions as initial and final states, respectively.     

Xe原子离子4d→f跃迁光电离截面延迟峰的研究

根据独立电子近似,本文研究了Xe原子离子4d→f跃迁光电离截面延迟峰。阐明了光电离截面延迟峰与对应末态光电子与原子离子实散射增强的关系,以及第二延迟峰与初、末通道量子数亏损差的关系。结果表明:(1)随着电离度的增加,光电离截面延迟峰向低能方向移动,最终消失而呈类氢结构;(2)对Xe离子,初、末通道量子数亏损差的绝对值越小,Cooper极小点的能量越低。 关键词：     

非整数量子跃迁

证明频率为v的辐射引起的量子跃迁中,跃迁系统始末两态能量差不必是hv的整数倍。跃迁的玻尔条件和光电效应的爱因斯坦定律都是微扰近似的结果,在强激光引起的跃迁中不成立。We prove that in the quantum transition of a system induced by the radiation of frequency v, the energy difference between the initial and the final states of the system is not necessarily being an integer multiple of hv. The Bohr condition for quantum transitions and the Einstein law for photo-electric effects are approximate results of perturbation. They are violated in the transitions induced by intense lasers.     

Xenon 5p–4d cascade emission upon 3d-photoionization

We investigated the photon-emission spectrum of Xe atoms upon photoionization of the Xe 3d-subshell. The 5p-4d spectrum is emitted in the process of the cascading decay of the 3d-vacancy and has a complex multi-component structure reflecting a great number of transitions from various ionic configurations produced during the cascade development. The spectrum is assigned by the direct construction of the cascade de-excitation tree. 21 different transitions between configurations of multiply charged Xe ions (+2 to +6) are found to be contributing to the spectrum. The 5p-4d partial fluorescence yield is found to be six times greater for the 3d-ionization than for the 4d-ionization. The effect of the multiplet splitting in the initial and final states of the emitting transitions is studied.     

The probabilistic symmetry breaking of periodic regimes rapidly passing through a zone of chaos into the transparency window

The problem of transition of a noisy dynamical system to a periodic oscillatory regime through a zone of chaos is considered. Using the noisy logistics map as an example, domains of attraction of energetically equivalent regimes of period three are found for various transition rates and various noise levels. The fine structure of the domains of attraction under the condition of fast transitions is revealed. It is discovered that the settling time of the stable cycle of period three heavily depends on the initial conditions, i.e., on the structure of the domains of attraction. The critical transition rate that separates the region of the probabilistic symmetry of final states from the region of the dynamic behavior of trajectories is estimated.     

Mean field methods for atomic and nuclear reactions: The link between time–dependent and time–independent approaches

Abstact: Three variants of mean field methods for atomic and nuclear reactions are compared with respect to both conception and applicability: The time–dependent Hartree–Fock method solves the equation of motion for a Hermitian density operator as initial value problem, with the colliding fragments in a continuum state of relative motion. With no specification of the final state, the method is restricted to inclusive reactions. The time–dependent mean field method, as developed by Kerman, Levit and Negele as well as by Reinhardt, calculates the density for specific transitions and thus applies to exclusive reactions. It uses the Hubbard–Stratonovich transformation to express the full time-development operator with two–body interactions as functional integral over one–body densities. In stationary phase approximation and with Slater determinants as initial and final states, it defines non–Hermitian, time–dependent mean field equations to be solved self–consistently as boundary value problem in time. The time–independent mean field method of Giraud and Nagarajan is based on a Schwinger–type variational principle for the resolvent. It leads to a set of inhomogeneous, non-Hermitian equations of Hartree–Fock type to be solved for given total energy. All information about initial and final channels is contained in the inhomogeneities, hence the method is designed for exclusive reactions. A direct link is established between the time–dependent and time–independent versions. Their relation is non–trivial due to the non–linear nature of mean field methods. Received: 7 January 1998 / Revised version: 20 April 1998