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

半导体纳米晶在基质中的高密度悬浮及其电子激发态的相干协同现象

基本信息

批准号：
07404014
负责人：
ITOH Tadashi
金额：
$ 23.55万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

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

该项目的目的是研究限制在半导体纳米晶中激子的光学性质以及激子内部结构，阐明单个纳米晶中激子之间的相互作用，并从实验和理论上研究纳米晶之间相干激子的协同现象。 .1）通过离子束溅射方法，我们制备了高密度悬浮在金属中的CdSe纳米晶，并制备了CdSe、ZnSe和我们通过X射线衍射和AFM形貌测量了薄膜的质量，并通过光学测量减少了晶体缺陷。2）限制激子态的光学研究a）在双光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，并提出了光子共振激发中固有的光学非马尔可夫过程。 b) 通过CuCl和ZnCdSe量子点的单点显微光谱，我们成功地观察到了激子发光的窄化、闪烁和光疲劳现象，我们发现第二低限制激子态的能量。与简单激子限制模型的预期有很大不同，并提出了 p 型限制态上偶极子自相互作用效应的可能性。c) 在 CuCl 中纳米晶体以高密度悬浮在聚合物中，我们发现在紫外激光照射下有一种特殊的发光增强现象，与多孔硅的情况类似，光电离或光诱导的表面结构变化被认为在这种现象中发挥了重要作用。 .d) Rydberg 1S 到 2P 激子态之间的光学跃迁已通过红外瞬态光谱测量。 2P激子偏离了激子平移运动的限制模型。计算出的1S到2P跃迁的理论光谱与实验结果在质量上一致。从这些结果来看，限制激子的研究在这两个方面都取得了进展。实验和理论，人们可以期待研究相干激子的协同现象的可能性。