电场对量子阱中激子能级宽度的影响

本文把固体中较大窨范围运动的粒子作为准经典粒子来描述。将已导出的能量测不准公式和激子的经典力学模型应用到电场下GaAs/GaAlAs量子阱中,激子能级宽度的计算结果与测量结果基本吻合,能较清楚、简单地解释纵向电场和横向电场下激子光吸收线宽的很大的差异。     

Splitting and storing excitons in strained coupled self-assembled quantum dots

We present a novel self-assembled quantum dot structure designed to spatially separate and store photo-generated electrons and holes in pairs of strain coupled quantum dots. The spatial separation of electron–hole pairs into quantum dots and strain-induced quantum dots has been investigated and verified by photoluminescence experiments. Results from time-resolved PL demonstrates that at low temperatures (3 K) the electron–hole pair can be stored for several seconds.     

Charged excitons in quantum dots: novel magnetic behavior and Auger processes

We describe theoretically multiply-charged excitons interacting with a continuum of delocalized states. Such excitons exist in relatively shallow quantum dots and have been observed in recent optical experiments on InAs self-assembled dots. The interaction of an exciton and delocalized states occurs via Auger-like processes. To describe the optical spectra, we employ the Anderson-like Hamiltonian by including the interaction between the localized exciton and delocalized states of the wetting layer. In the absence of a magnetic field, the photoluminescence line shapes exhibit interference effects. When a magnetic field is applied, the photoluminescence spectrum demonstrates anticrossings with the Landau levels of the extended states. We show that the magnetic-field behavior of charged excitons is very different to that of diamagnetic excitons in three and two-dimensional systems.     

Interface charge transfer between metal phthalocyanine and fluorinated hexaazatrinaphthylene molecules

A typical donor/accepter (D/A) interface made of fluorinated hexaazatrinaphthylene (HATANA-F6) and metal phthalocyanine (MPc) molecules has been studied by photoelectron spectroscopy. Planar shape copper phthalocyanine (CuPc) and non-planar titanyl phthalocyanine (TiOPc) molecules show contrast behavior of D/A interface charge transfer (CT), though the electron affinity of HATANA-F6 is smaller than the ionization potential (IP) of both MPcs. While the CuPc/HATNA-F6 interface has no clue for the CT, the TiOPc/HATNA-F6 has an indication of interface CT-induced band bending. Not only the difference in IP but also molecular shape and interface geometry at D/A contact largely affect the characteristics of CT state formation.     

Energy migration and transfer between chromophores embedded in Gaussian space

We have used a Monte Carlo method to investigate energy migration and transfer between chromophores embedded in Gaussian space. In using this method we have obtained fluorescence quantum yields, fluorescence depolarization, and the respective decay profiles of donor fluorescence. It was shown that all photophysical observables are dependent upon the number of donor and acceptor chromophores and upon the Förster radii ratio. The latter feature is particularly interesting, and it indicates the existence of correlations between donor and acceptor chromophores. It was shown that the excitation of the donor chromophore at the origin leads to different values of observables, in comparison with an excitation of a randomly selected donor chromophore. The results presented show the importance of the averaging procedures needed to be developed while dealing with specific distribution functions, as, for example, in the case of energy migration and trapping in aromatic polymers and copolymers.     

Study on the chemiluminescence resonance energy transfer between luminol and fluorescent dyes using a linear CCD spectrometer

Chemiluminescence (CL) has been a useful tool for analytical applications. Fluorescein can be used to enhance CL emission of luminol. With three-dimensional (3D) dynamic CL spectrum obtained from a linear CCD (charge-coupled device) flow-injection CL spectrometer, the fluorescein enhanced CL analysis was studied. The enhanced process can be described with chemiluminescence resonance energy transfer (CRET) at certain fluorescein concentrations. In the process of CRET, fluorescein enlarges CL intensity but does not join the CL reaction. Compared with classic luminol-Co²⁺ CL system, the fluorescein-enhanced system exhibits stronger CL signal with the linear range and detection limit for traces of Co²⁺ unchanged.     

Energy transfer and quantum correlation dynamics in FMO light-harvesting complex

The dynamics of energy transfer in Fenna–Matthews–Olson (FMO) light-harvesting complex interacting with a phonon bath is investigated. In this contribution, by considering the phonon bath as a source of stochastic noise, a new approach is proposed. Also, by calculating the global quantum entanglement and global quantum discord, the time evolution of the quantum correlation during the process is evaluated. The effects of temperature and initial excited state on the energy transfer and the quantum correlation are studied. It is shown, in agreement with the previous results, that the increasing of the temperature gives rise to the faster delocalisation of energy transfer and global quantum entanglement in the FMO complex. The proposed model predicts that the global discord is resistance versus the raising temperature. Furthermore, it is demonstrated that the quantum entanglement with respect to the global quantum discord has a significant role in the process of energy transfer in the FMO complex.     

Surface plasmon enhanced quantum transport in a hybrid metal nanoparticle array

Hybrid Pd–Ag nanoparticle arrays composed of randomly distributed Pd nanoparticles in dense packing and a small number of dispersed Ag nanoparticles were fabricated with controlled coverage. Photo-enhanced conductance was observed in the nanoparticle arrays. Largest enhancement, which can be higher than 20 folds, was obtained with 450 nm light illumination. This wavelength was found to correlate with the surface plasmon resonance of the Ag nanoparticles. Electron transport measurements showed there were significant Coulomb blockade in the nanoparticle arrays and the blockade could be overcome with the surface plasmon enhanced local field of Ag nanoparticles induced by light illumination.     

Effect of electric field on the enhanced heat transfer characteristic of an evaporator with multilayered sintered copper mesh

In this paper, it was investigated experimentally that the effect of different kinds of working fluid on the thermal performance of evaporator with capillary wick consisted by multilayered sintered copper mesh under different electric field strengths at the operating pressure of 1.01 × 10⁵ Pa R141b and R123 were used as the working fluids. The electric field strength in this study was in the range of 0kV/m–1600 kV/m, respectively. The experimental results showed that the applied electric field strength has significant effect on heat transfer characteristic. The heat transfer enhancement effects increased with the increase of the electric field. Under the applied electric field strength, the maximum heat transfer enhancement factors could reach as high as 1.5 and 1.32 for the two kinds of working fluids in the experiment.     

Energy transfer studies in dye mixtures in different solvent environments

The energy transfer mechanism in C 540–rhodamine 6G and C 540–rhodamine B donor–acceptor (D–A) pairs is investigated. The good spectral overlap and the proximity of D–A pair molecules, which is around 60 Å, denote the possibility of resonance energy transfer between the D–A pairs. Energy transfer is studied in two solvent environments. C 540–Rh 6G and C 540–RhB D–A pairs behave in quite different manner in different solvent environments.     

Magnetic field effect on transitions between direct and indirect excitons in diluted magnetic semiconductor double quantum wells

Transitions between direct and indirect excitons with change of magnetic field in double quantum well heterostructure Cd_1−xMg_xTe/Cd_1−yMg_yTe/Cd_1−xMg_xTe/Cd_1−zMn_zTe/Cd_1−xMg_xTe in external magnetic field are studied. The structure contains diluted magnetic semiconductor (Cd,Mn)Te layer that forms magnetic quantum well with the depth depending on the magnetic field intensity. Above some magnetic field the indirect exciton becomes the lowest excited state of the system. The indirect exciton lifetime exceeds by several orders of magnitude of the direct exciton one. The range of quantum well widths for which the indirect exciton is the exciton lowest state was estimated for the proposed system.     

Energy transfer and excited state lifetime of some anthracene laser dyes

The lifetimes of some anthrathene derivatives in different solvents have been determined using the phase modulation method. The lifetime of 10-phenyl-2-methyl-9-acetoxyanthracene and 10-(4-acetoxyphenyl)-2-methyl-9-acetoxyanthracene were found to equal 11 and 11 ns in methanol, respectively. Energy transfer from 10-phenyl-2-methyl-9-acetoxyanthracene and 10-(4-acetoxyphenyl)-2-methyl-9-acetoxyanthracene to rhodamine B and rhodamine 110 in different solvents has been studied by using steady-state emission measurements. The large values of the critical transfer distance R₀ and the rate constant of energy transfer k_ET suggest that the mechanism is long-range dipole–dipole energy transfer as described by Förster.     

Enhanced luminescence of rare-earthTb (III) by Tm (III) in bis(benzoylmethyl) sulfoxide complexes and intra-molecular energy transfer

Rare-earth complexes [(Tb_xTm_y)L₅(ClO₄)₂](ClO₄)·3H₂O(x:y=1.000:0.000, 0.999:0.001, 0.995:0.005, 0.990:0.010, 0.950:0.050, 0.900:0.100, 0.800:0.200, 0.700:0.300; L=C₆H₅COCH₂SOCH₂COC₆H₅) were synthesized and characterized with elemental analysis, infrared spectra (IR) and ¹H NMR. The photophysical properties of these complexes were studied in detail with ultraviolet absorption spectra, fluorescent spectra and lifetimes. The fluorescence spectra and decay curves of complexes indicated that the fluorescence emission intensity was enhanced and the fluorescence lifetime was prolonged by Tm (III), which may be due to the intra-molecular energy transfer between inert rare-earth ions and active rare-earth ions. The complexes showed the best properties when the mole ratio of Tb (III) to Tm (III) is 0.995:0.005. The intensity of fluorescence can be increased to 208%. Additionally, the energy-transfer mechanisms between the ligand and the central Tb (III) ions were discussed.     

Energy transfer rate in double-layer graphene systems: Linear regime

We theoretically investigate the energy transfer phenomenon in a double-layer graphene (DLG) system. We use the balance equation approach in linear regime and random phase approximation screening function to obtain energy transfer rates at different electron temperatures, densities and interlayer spacings. We find that the rate of energy transfer in the DLG is qualitatively similar to that obtained in the double-layer two-dimensional electron gas but its values are an order of magnitude greater. Also, at large electron temperature differences between two graphene layers, the electron density dependence of energy transfer is significantly different, particularly in case of unequal electron densities.     

Energy transfer between Sm and Er in orthophosphate YPO4

The energy transfer between Sm³⁺ and Er³⁺ ions in yttrium orthophosphate is studied. This choice of ions is based on the possibility of quantum cutting processes and the host material is selected according to the position of the 5d bands of the Sm³⁺ ion. The Sm³⁺ and Er³⁺ doped and Sm³⁺, Er³⁺ co-doped YPO₄ have been synthesized. Spectroscopic studies were done in the ultraviolet and vacuum ultraviolet ranges. The energy transfer between Sm³⁺ and Er³⁺ is very efficient but it does not lead to Er³⁺ visible emission. Whatever the excitation wavelength, the emission of co-doped samples mainly occurs in the infrared range.     

Energy transfer between two aggregates in light-harvesting complexes

Energy transfer processes between two aggregates in a coupled chromophoric-pigment(protein)system are studied via the standard master equation approach.Each pigment of the two aggregates is modeled as a two-level system.The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate.The model can be used to theoretically simulate many aspects of light-harvesting complexes(LHCs).By applying the real bio-parameters of photosynthesis,we numerically investigate the efficiency of energy transfer(EET)between the two aggregates in terms of some factors,e.g.,the initial coherence of the donor aggregate,the coupling strengthes between the two aggregates and between different pigments,and the effects of noise from the environment.Our results provide evidence for that the actual numbers of pigments in the chromophoric rings of LHCs should be the optimum parameters for a high EET.We also give a detailed analysis of the effects of noise on the EET.     

Charge transfer between sensing and targeted metal nanoparticles in indirect nanoplasmonic sensors

In indirect nanoplasmonic sensors, the plasmonic metal nanoparticles are adjacent to the material of interest, and the material-related changes of their optical properties are used to probe that material. If the latter itself represents another metal in the form of nanoparticles, its deposition is accompanied by charge transfer to or from the plasmonic nanoparticles in order to equalize the Fermi levels. We estimate the value of the transferred charge and show on the two examples, nanoparticle sintering and hydride formation, that the charge transfer has negligible influence on the probed processes, because the effect of charge transfer is less important than that of nanoparticle surface energy. This further corroborates the non-invasive nature of nanoplasmonic sensors.     

Energy transfer dynamics between Alq3 and CdTeS/ZnS core shell nanocrystals

The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum dots (QDs) as the guest and organic small-molecule material Alq₃ as the host, are studied by steady-state and time-resolved PL spectroscopy. Both the relative intensity and the PL lifetime are intensively dependent on the weight ratio of Alq₃ and CdTeS/ZnS QDs. The detailed analysis provides clear evidence for a Förster energy transfer from Alq₃ host to QDs guest, based on the nonradiative resonant transfer mechanism. The results are relevant to the application of hybrid organic/inorganic systems to OLEDs.     

Flow boiling heat transfer enhancement under ultrasound field in minichannel heat sinks

The enhancement of the heat transfer assisted by ultrasound is considered to be an interesting and highly efficient cooling technology, but the investigation and application of ultrasound in minichannel heat sinks to strengthen the flow boiling heat transfer are very limited. Herein, a novel installation of ultrasound transducers in the flow direction of a minichannel heat sink is designed to experimentally study the characteristics of heat transfer in flow boiling and the influence of operation parameters (e.g., heat flux, mass flux rate) and ultrasound parameters (e.g., frequency, power) on the flow boiling heat transfer in a minichannel heat sink with and without ultrasound field. Bubble motion and flow pattern in the minichannel are analyzed by high-speed flow visualization, revealing that the ultrasound field induces more bubbles at the same observation position and a forward shift of the onset of nucleation boiling along the flow direction, as ultrasonic cavitation produces a large number of bubbles. Moreover, bubbles hitting the channel wall on the left and right sides are found, and the motion speed of the bubbles is increased by 31.9% under the ultrasound field. Our results demonstrate that the heat transfer coefficient obtained under the ultrasound field is 53.9% higher than in the absence of the ultrasound field under the same conditions, and the enhancement ratio is decreased in the high heat flux region due to the change of the flow regime with increasing heat flux. This study provides a theoretical basis for the application of an ultrasound field in minichannel heat sinks for the enhancement of flow boiling heat transfer.     

光子晶体中双通道之间能量的转移

从理论和实验上分析了光子晶体中双通道之间能量的转移.在双通道之间引入复合型光子晶体波导,通过调节复合型波导的内部参数，使其满足一定的条件，就可以实现双通道之间能量的完全转移，从而实现了光的定向传输.在实验中，测得了输出端的透过谱. 关键词： 复合型光子晶体波导 能量转移 定向传输