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Photoluminescence Enhancement through Symmetry Breaking Induced by Defects in Nanocrystals
Nano Letters ( IF 9.6 ) Pub Date : 2017-07-21 00:00:00 , DOI: 10.1021/acs.nanolett.7b01662 Peter C. Sercel 1 , A. Shabaev 2 , Al. L. Efros 3
Nano Letters ( IF 9.6 ) Pub Date : 2017-07-21 00:00:00 , DOI: 10.1021/acs.nanolett.7b01662 Peter C. Sercel 1 , A. Shabaev 2 , Al. L. Efros 3
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We present a theoretical model for the effect of symmetry breaking introduced by the doping of semiconductor nanocrystals with Coulomb impurities. The presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through the mixing of the hole spin and parity sublevels, breaking the selection rules responsible for the exciton dark state in undoped nanocrystals. After reviewing the effects on the exciton fine structure and optical selection rules using symmetry theory, we present a perturbative model to quantify the effects. We find that the symmetry breaking proceeds by two mechanisms: First, mixing by even parity terms in the Coulomb multipole expansion results in an exciton fine structure consisting of three optically active doublets which are polarized along x, y, and z axes with a ground optically passive dark exciton state, and second, odd parity terms which break inversion symmetry significantly activate optical transitions which are optically forbidden in the unperturbed nanocrystal due to both spin and parity selection rules. In the case of small sized “quasi-spherical” nanocrystals, the introduction of a single positively charged Coulomb center is shown here to result in significant enhancement of the radiative decay rate at room temperatures by up to a factor of 10.
中文翻译：
通过纳米晶体中的缺陷引起的对称性破坏来增强光致发光。
我们提出了一种对称模型的影响的理论模型，该模型是通过用库仑杂质掺杂半导体纳米晶体而引入的。库仑中心的存在破坏了纳米晶体的对称性，并通过空穴自旋和奇偶校验子级的混合影响了其光学性能，打破了导致未掺杂纳米晶体中激子暗态的选择规则。在使用对称理论回顾了对激子精细结构和光学选择规则的影响之后，我们提出了一种微扰模型来量化影响。我们发现对称性破坏是通过两种机制进行的：首先，在库仑多极扩展中按偶数奇偶项进行混合会产生由三个沿x偏振的旋光双峰组成的激子精细结构，y和z轴具有光学被动暗激子态，以及打破反演对称性的第二奇数奇偶校验项会显着激活由于自旋和奇偶选择规则而在不受干扰的纳米晶体中被光学禁止的光学跃迁。对于小尺寸的“准球形”纳米晶体，此处所示的单个带正电的库仑中心的引入可导致室温下的辐射衰减率显着提高多达10倍。
更新日期：2017-07-22
中文翻译：
通过纳米晶体中的缺陷引起的对称性破坏来增强光致发光。
我们提出了一种对称模型的影响的理论模型，该模型是通过用库仑杂质掺杂半导体纳米晶体而引入的。库仑中心的存在破坏了纳米晶体的对称性，并通过空穴自旋和奇偶校验子级的混合影响了其光学性能，打破了导致未掺杂纳米晶体中激子暗态的选择规则。在使用对称理论回顾了对激子精细结构和光学选择规则的影响之后，我们提出了一种微扰模型来量化影响。我们发现对称性破坏是通过两种机制进行的：首先，在库仑多极扩展中按偶数奇偶项进行混合会产生由三个沿x偏振的旋光双峰组成的激子精细结构，y和z轴具有光学被动暗激子态，以及打破反演对称性的第二奇数奇偶校验项会显着激活由于自旋和奇偶选择规则而在不受干扰的纳米晶体中被光学禁止的光学跃迁。对于小尺寸的“准球形”纳米晶体，此处所示的单个带正电的库仑中心的引入可导致室温下的辐射衰减率显着提高多达10倍。
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