High Density Suspension of Semiconductor Nanocrystals in Matrices and Their Coherent Cooperative Phenomena among Electronic Excited States

本项目的目的是研究半导体纳米晶体中激子的光学性质和激子的内部结构，阐明激子之间的相互作用，并从实验和理论上研究纳米晶体之间相干激子的合作现象。1）利用离子束溅射方法，我们已经制备了高密度的纳米颗粒悬浮的CdSe，并且还制备了CdSe，ZnSe和ZnO纳米颗粒薄膜。通过X射线衍射和原子力显微镜形貌测量，得到了薄膜的质量，并通过光学测量得到了晶体缺陷的减少情况。2）受限激子态的光学研究a）在双光子共振激发下进行了皮秒时间分辨发光测量。我们测量了共振发光和共振散射之间的比率的尺寸依赖性，并提出了纳米晶体中固有的光学非马尔可夫过程。B）通过单点测量， ...更多信息 通过对CuCl和ZnCdSe量子点的显微光谱研究，成功地观察到了激子发光的窄化、闪烁和光疲劳现象。我们发现次低受限激子态的能量与简单激子受限模型的预期能量有很大的不同，并提出了偶极自相互作用对p型受限态的影响的可能性。c）在高密度悬浮于聚合物中的CuCl纳米晶中，我们发现了紫外激光照射下发光增强的奇特现象。与多孔硅的情况类似，光致电离或光致表面结构的变化被认为在这一现象中起重要作用。d）用瞬态红外光谱测量了里德伯1S到2P激子态之间的光学跃迁。随着纳米晶体尺寸的减小，2P激子的约束偏离了激子平移运动的约束模型。对1S到2P跃迁的理论计算结果与实验结果定性地吻合，从而在理论和实验上都取得了一定的进展，并为研究相干激子的合作现象提供了可能。少

The aim of this project is to investigate the optical properties of excitons confined in semiconductor nanocrystals together with exciton internal structures, to clarify the mutual interaction among excitons in one nanocrystal, and also to study cooperative phenomena of coherent excitons between nanocrystals both in experiment and theory.1) By means of ion beam sputtering method, we have made CdSe nanocrystals suspended in metrices with high density and also made CdSe, ZnSe and ZnO ultrathin films. We have got the quality of films by X ray diffraction and AFM topography, and the reduction of crystal defects by optical measurement.2) Optical investigation of confined exciton statesa) Picosecond time-resolved luminescence measurement has been perfomed under two-photon resonant excitation. We have measured the size dependence of the ratio between resonant luminescence and resonant scattering and proposed the optical non-Markov processes inherent in nanocrystals.b) By means of single-dot m … More icrospectroscopy of CuCl and ZnCdSe quantum dots, we have succeeded to observe the narrowing, blinking and photofatigue phenomena of exciton luminescence. We have found that the energy of the second lowest confined exciton state is considerably different from that expected for simple exciton confinement model and suggested the possibility of dipole self interaction effect on p-type confined states.c) In CuCl nanocrystals suspended in polymer at high density, we have found a peculiar phenomenon of luminescence enhancement under ultraviolet laser irradiation. Similar to the case of porous Si, photoionization or photo-induced change of surface structure has been considered to play an important role in this phenomenon.d) The optical transition between Rydberg 1S to 2P exciton states has been measured by means of infrared transient spectroscopy. As the size of nanocrystals decreases, the confinement of the 2P exciton deviates from the model of the confinement of exciton translational motion. Theoretical spectra calculated for the 1S to 2P transition is found to coincide qualitatively with the experimental ones.From these results, a progress in the study of confined excitons has been achieved both in experiment and theory and one can expect a possibility of studying the cooperative phenomena of coherent excitons. Less