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A Model for Optical Gain in Colloidal Nanoplatelets

Abstract

Cadmium chalcogenide nanoplatelets (NPLs) and their heterostructures have been reported to have low gain thresholds and large gain coefficients, showing great potentials for lasing applications. However, further improvement of optical gain properties of NPLs is hindered by a lack of models that can account for their optical gain characteristics and predict its dependence on material properties (such as lateral size, concentration, and/or optical density). Herein, we report a systematic study of optical gain (OG) in 4-monolayer thick CdSe NPLs by both transient absorption spectroscopy study in colloidal solutions and amplified spontaneous emission (ASE) measurement of thin films. We showed that OG threshold is not while the saturation gain amplitude is dependent on the NPL lateral area when comparing samples with the same optical density at the excitation wavelength. Both OG and ASE thresholds increase with the optical density at the excitation wavelength for samples of the same NPL thickness and lateral area. We proposed an OG model for NPLs that can successfully account for the observed lateral area and optical density dependences. The model reveals that OG originates from stimulated emission from bi-exciton states and OG threshold is reached when the average number of excitons per NPL exceeds about half occupation of bandedge exciton states. The model can also rationalize the much lower OG thresholds in NPLs compared to QDs. This work provides a microscopic understanding of the dependence of OG properties on the morphology of colloidal nanocrystals and important guidance for rational optimization lasing performance of NPLs and other low dimensional nanocrystals.

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Publication details

The article was received on 03 Oct 2017, accepted on 13 Nov 2017 and first published on 13 Nov 2017


Article type: Edge Article
DOI: 10.1039/C7SC04294A
Citation: Chem. Sci., 2017, Accepted Manuscript
  • Open access: Creative Commons BY license
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    A Model for Optical Gain in Colloidal Nanoplatelets

    Q. Li and T. Lian, Chem. Sci., 2017, Accepted Manuscript , DOI: 10.1039/C7SC04294A

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