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Spectroscopic study of micro-crystals of thallium halides

卤化铊微晶的光谱研究

基本信息

批准号：
09640402
负责人：
FUJII Atsuhiro
金额：
$ 1.73万
依托单位：
Kumamoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640402/
关键词：
Micro-crystal Thallium halide Quantum size effect exciton Quantum confinement Exchange interaction Optical absorption

项目摘要

The extrema of the valence band and the conduction band of thallium halides are not at the GAMMA point but at the X point. As the result, the direct exciton has a unique and complex structure due to intervallay exchange and Coulomb interaction. In the present research we intended to study quantum size effects on an exciton state and on exchange interaction of the exciton in a micro-crystal of thallium halides.Quantum size effects on electron states have been extensively studied theoretically in these years. Kayanuma studied an exciton state in a spherical potential well to the full extent both analytically and numerically.We measured optical absorption spectra of the direct exciton of TlCI and TlBr in evaporated thin films at 5K and determined the size R of micro-crystals of TICI and TIBr by an electron microscope. The energy of the exciton was found to increase with decreasing micro-crystal size. The energy shift of the exciton was followed very well to Kayamuna's theoretical value for rather wide range of micro-crystal size R from the regime of individual particle confinement R/alpha<less than or equal>2 in the regime of exciton confinement R/alpha<greater than or equal>4, where a is the effective Bohr radiusIn TICI the absorption spectrum of the lowest exciton state has doublet peaks labeled 1A and 1B.We found that the relative intensity of the absorption bands 1A to 1B decreased with decreasing the micro-crystal size and disappeared in the film where the micro-crystal size was less than lOnm. The experimental results suggest that the exchange interaction play more important role in smaller micro-crystals. It is still open what is the confinement effect on these exchange interactions, and futher experiment and theoretical investigations will be required.

卤化铊的价带和导带的极值不在Gamma点，而在X点。结果表明，由于间隔交换和库仑相互作用，直接激子具有独特而复杂的结构。本文研究了卤化铊微晶中激子态的量子尺寸效应和激子交换相互作用的量子尺寸效应。Kayanuma等人对球势阱中激子态进行了全面的解析和数值研究，我们测量了5 K下TlCl和TlBr在蒸发薄膜中的直接激子的光吸收谱，并用电子显微镜测定了TlCl和TlBr微晶的尺寸R。发现激子的能量随着微晶尺寸的减小而增加。激子的能量位移非常好地遵循Kayamuna的理论值，对于相当宽范围的微晶尺寸R，从<less than or equal>激子限制R/α 4的制度中的单个粒子限制R/α 2<greater than or equal>的制度，在TICI中，最低激子态的吸收谱有双峰1A和1B，发现1A-1B吸收带的相对强度随微区的减小而减小，1A-1B吸收带的相对强度随微区的减小而减小，1B吸收带的相对强度随微区的减小而减小。在微晶尺寸小于10 nm的薄膜中，实验结果表明，交换作用在较小的微晶中起着更重要的作用。限制效应对这些交换作用的影响还有待进一步的实验和理论研究。