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基于飞秒时间分辨瞬态吸收和多元瞬态光栅光谱技术对全反式Astaxanthin(AXT)在DMSO溶剂中的超快激发态弛豫动力学进行了观测.结果表明,光激发后AXT/DMSO体系直接发生S_0→S_2跃迁,基态漂白对应光谱范围为420~550nm.由S_2→S_1的内转换过程发生的时间常数为120~160fs.S_1态激发态吸收对应的光谱范围为550~740nm,基态漂白恢复过程对应的是S_1→S_0的内转换过程,其时间尺度为4.50~5.50ps. 相似文献
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本文以三个不同粒径(1#:2.3 nm, 2#:2.8 nm和3#:3.5 nm)的巯基乙酸包覆的CdTe量子点(thioglycolic acid capped CdTe quantum dots, TGA-CdTe QDs)样品为研究对象, 其时间相关单光子计数(time-correlated single photon counting, TCSPC)实验得到的时间分辨光谱显示, 三个量子点的荧光平均寿命依次是~6 ns, ~10 ns和~12 ns, 其动力学过程包括慢过程和快过程两部分. 随其粒径尺寸的增加, 其慢过程延长, 快过程在变短. 然后, 通过瞬态吸收和荧光上转换两种基于飞秒的时间分辨光谱技术, 对TGA-CdTe量子点的带间弛豫过程做了探究. 实验结果显示, 三个TGA-CdTe量子点样品, 随其粒径增大, 最高激发态和最低激发态填充速率减慢, 其中, 最高激发态从0.33 ps增加至0.79 ps; 最低激发态从0.53 ps增至~1 ps. 另外, 由瞬态吸收和荧光上转换两种时间分辨手段相结合, 可得到CdTe量子点带间弛豫的完整图像, 结果显示了TGA-CdTe 量子点的一个本征特征:即在基态漂白恢复过程中的初始上升阶段, 荧光上转换信号要慢于瞬态吸收信号. 这可以为量子点在光电转换应用上提供帮助. 相似文献
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用分子束外延在GaAs衬底上生长了CdSe/CdMnSe多量子阱结构.利用X射线衍射(XRD)、变密度激发的PL光谱、变温度PL光谱和变密度激发的ps时间分辨光谱研究了CdSe/CdMnSe多量子阱结构和激子复合特性.讨论了随温度升高辐射线宽展宽和辐射复合效率降低的机理.发现不同激发密度下发光衰减时间不同,认为它的机理可能是无辐射复合引起的.在该材料中观测到激子激子散射发射峰,它被变密度激发和变温度PL光谱所证实.
关键词:
CdSe/CdMnSe
量子阱
光学性质 相似文献
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测定了亚单层InGaAs/GaAs量子点-量子阱异质结构在5K下的时间分辨光致发光谱.亚单层量 子点的辐射寿命在500 ps 至 800 ps之间,随量子点尺寸的增大而增大,与量子点中激子的 较小的横向限制能以及激子从小量子点向大量子点的隧穿转移有关.光致发光上升时间强烈 依赖于激发强度密度.在弱激发强度密度下,上升时间为 35 ps,纵光学声子发射为主要的 载流子俘获机理.在强激发强度密度下,上升时间随激发强度密度的增加而减小,俄歇过程 为主要的载流子俘获机理.该结果对理解亚单层量子点器件的工作特性非常有用.
关键词:
亚单层
量子点-量子阱
时间分辨光致发光谱 相似文献
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Magnetooptics and dynamics of a magnetic polaron in semimagnetic CdSe/ZnMnSe quantum dots 总被引:1,自引:0,他引:1
The magnetooptics and picosecond dynamics of the radiative recombination of excitons in self-assembled semimagnetic CdSe/ZnMnSe quantum dots is studied at low temperatures. The behavior of individual quantum dots in a magnetic field and with an increase in temperature is indicative of a strong exchange interaction of excitons and magnetic Mn ions giving rise to a quasi-zero-dimensional exciton magnetic polaron. When the exciton energy exceeds the intracenter transition energy in Mn, the energy is rapidly transferred from excitons to Mn ions (faster than 20 ps). In the opposite case, a substantial red shift (~15 meV) of the emission line maximum is observed during the exciton lifetime ~500 ps, presenting the dynamics of the formation of a magnetic polaron with a characteristic time of ~110 ps. 相似文献
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S. Corni M. Braskn M. Lindberg J. Olsen D. Sundholm 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):436-442
Recombination and stabilization energies of multiexcitons confined in positively and negatively charged semiconductor InGaAs/GaAs quantum dot (QD) samples have been studied by employing large-scale configuration interaction (CI) calculations. The CI calculations show that at most six electrons or two holes can be confined in the QD. Multiply charged multiexciton complexes with up to five excess electrons or two excess holes are also found to be stable, even when a few electron–hole pairs are present in the QD. The chemical potential functions for charged QD samples do not possess the pronounced stepped form as obtained for the corresponding neutral multiexciton complexes. The negatively and the positively charged excitons (negative and positive trions) lie lower in energy as compared to a neutral exciton and a single non-interacting charge carrier in the lowest single-particle state of another quantum dot. The other charged multiexciton complexes studied are not confined with respect to the corresponding neutral multiexciton and a non-interacting charge carrier. To include the contributions from the heavy-hole light-hole (HH–LH) coupling, a perturbative treatment of the band-mixing effects was implemented. The perturbation-theory calculations show that the HH–LH coupling does not shift the energies in the present InGaAs/GaAs QD sample. 相似文献
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单层过渡金属硫化物由于其特有的激子效应以及强自旋-谷耦合性质,在光电子学及谷电子学等方面有着很广阔的应用前景.利用超快时间分辨光谱,本文系统地比较了两类钨基单层硫化物(WS_2和WSe_2)的A-激子动力学和谷自旋弛豫特性.实验结果表明, WS_2单层膜的A-激子弛豫表现为双指数过程,而对于WSe_2,其A-激子衰减表现为三指数过程,且激子的寿命远长于前者. WS_2谷自旋极化弛豫表现为单指数衰减,其寿命约0.35 ps,主要由电子-空穴交换作用所主导.而对于WSe_2,谷自旋弛豫表现出双指数弛豫特性:一个寿命为0.5 ps的快过程和一个寿命为28 ps的慢过程.快过程的弛豫来源于电子-空穴交换作用,而慢过程则由于自旋晶格散射形成暗激子的过程.通过调谐抽运光波长,进一步证实WSe_2较WS_2更容易形成暗激子. 相似文献
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T. S. Shamirzaev 《Physics of the Solid State》2018,60(8):1554-1567
The behavior of excitons in heterostructures with indirect-gap GaAs/AlAs quantum wells and (In, Al)As/AlAs quantum dots is discussed. The possibilities of controlled change of the exciton radiative recombination time in the range from dozens of nanoseconds to dozens of microseconds, experimental study of the spin dynamics of long-lived localized excitons, and use of the optical resonant methods for exciting the indirect-band exciton states are demonstrated. 相似文献
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Ultrafast proton transfer dynamics of 2-(2'-hydroxyphenyl)benzoxazole dye in different solvents 下载免费PDF全文
The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy. 相似文献
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《Physica E: Low-dimensional Systems and Nanostructures》2011,43(10):2493-2496
Coherent spin precession of electrons and excitons is observed in charge tunable InP quantum dots under the transverse magnetic field by means of time-resolved Kerr rotation. In a quantum dot doped by one electron, spin precession of the doped electron in the quantum dot starts out of phase with spin precession of the doped electrons in a GaAs substrate just after a trion is formed and persists for more than 2 ns even after the trion recombines. Simultaneously spin precession of a trion (hole) starts. Observation of spin precession of both a doped electron and a trion (hole) confirms creating coherent superposition of an electron and a trion as the initialization process of spin of doped electrons in quantum dots. In a neutral quantum dot, the exciton spin precession starts out of phase with spin precession of the doped electrons in a GaAs substrate and the precession frequency does not converge to 0 at the zero field limit. It contains the electron–hole exchange interaction and corresponds to the splitting between bright and dark excitons under the transverse magnetic field. 相似文献
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Radiative lifetimes of free-atom transitions, scaled by ω3 for comparison at 368 nm, are not faster than about 6.9 ns. BaF2 core-valence luminescence, scaled in the same way from 220 to 368 nm, corresponds to 4.1 ns. In contrast, excitonic transitions in wide-gap semiconductors display subnanosecond radiative lifetimes, and in particular ZnO has radiative lifetimes measured at 50–300 ps for Do,X and 400–900 ps for free excitons. The “giant oscillator strength” corresponding to these lifetimes can be explained by theories developed initially for defect-bound excitons, then quantum wells, and nanoparticles. An exciton is a coherent array of N dipoles, where N is the number of sites covered by coherent translational motion of the exciton. This is not essentially a phenomenon of multiple excitons, but applies as well to single-exciton decay. It differs in that regard from the more familiar Dicke giant dipole of N coherently excited atoms lacking translational periodicity. The phenomenon suggests possibilities for achieving ultrafast scintillators and high light yield. 相似文献
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Auger processes are investigated for CdS/ZnS core-shell quantum dots. Auger recombination (AR) lifetime and electron relaxation inside the core are computed. Using the effective-mass theory and by solving a three-dimension Schrödinger equation we predict the dependence of Auger relaxation on size of core-shell nanocrystals. We considered in this work different AR processes: the excited electron (EE), excited hole (EH), multiexciton AR type. Likewise, Auger multiexciton recombination rates are predicted for biexciton. Our results show that biexciton AR type is more efficient than the other AR process (excited electron (EE) and excited hole (EH)). We also found that electron Auger relaxation P→S is very efficient in core-shell nanostructures. 相似文献
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Auger rates are calculated for CdSe colloidal quantum dots using atomistic empirical pseudopotential wave functions. We predict the dependence of Auger electron cooling on size, on correlation effects (included via configuration interaction), and on the presence of a spectator exciton. Auger multiexciton recombination rates are predicted for biexcitons as well as for triexcitons. The results agree quantitatively with recent measurements and offer new predictions. 相似文献
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R.J. Warburton B. Urbaszek E.J. McGhee C. Schulhauser A. Hgele K. Karrai B.D. Gerardot P.M. Petroff 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):45
By embedding a layer of self-assembled quantum dots into a field-effect structure, we are able to control the exciton charge in a single dot. We present the results of photoluminescence experiments as a function of both charge and magnetic field. The results demonstrate a hierarchy of energy scales determined by quantization, the direct Coulomb interaction, the electron–electron exchange interaction, and the electron–hole exchange interaction. For excitons up to the triply charged exciton, the behavior can be understood from a model assuming discrete levels within the quantum dot. For the triply charged exciton, this is no longer the case. In a magnetic field, we discover a coherent interaction with the continuum states, the Landau levels associated with the wetting layer. 相似文献