Geiregat Pieter, Houtepen Arjan J, Sagar Laxmi Kishore, Infante Ivan, Zapata Felipe, Grigel Valeriia, Allan Guy, Delerue Christophe, Van Thourhout Dries, Hens Zeger
Physics and Chemistry of Nanostructures group, Ghent University, B-9000 Gent, Belgium.
Photonics Research Group, Ghent University, B-9000 Gent, Belgium.
Nat Mater. 2018 Jan;17(1):35-42. doi: 10.1038/nmat5000. Epub 2017 Oct 9.
Colloidal quantum dots (QDs) raise more and more interest as solution-processable and tunable optical gain materials. However, especially for infrared active QDs, optical gain remains inefficient. Since stimulated emission involves multifold degenerate band-edge states, population inversion can be attained only at high pump power and must compete with efficient multi-exciton recombination. Here, we show that mercury telluride (HgTe) QDs exhibit size-tunable stimulated emission throughout the near-infrared telecom window at thresholds unmatched by any QD studied before. We attribute this unique behaviour to surface-localized states in the bandgap that turn HgTe QDs into 4-level systems. The resulting long-lived population inversion induces amplified spontaneous emission under continuous-wave optical pumping at power levels compatible with solar irradiation and direct current electrical pumping. These results introduce an alternative approach for low-threshold QD-based gain media based on intentional trap states that paves the way for solution-processed infrared QD lasers and amplifiers.
胶体量子点（QDs）作为可溶液处理且可调谐的光学增益材料，越来越受到关注。然而，特别是对于红外活性量子点，光学增益仍然效率低下。由于受激辐射涉及多重简并的带边态，只有在高泵浦功率下才能实现粒子数反转，并且必须与高效的多激子复合竞争。在此，我们表明碲化汞（HgTe）量子点在整个近红外电信窗口表现出尺寸可调的受激辐射，其阈值是之前研究的任何量子点都无法比拟的。我们将这种独特行为归因于带隙中的表面局域态，这些态将HgTe量子点转变为四能级系统。由此产生的长寿命粒子数反转在与太阳辐射和直流电泵浦兼容的功率水平下，通过连续波光泵浦诱导放大的自发辐射。这些结果引入了一种基于有意陷阱态的低阈值量子点增益介质的替代方法，为溶液处理的红外量子点激光器和放大器铺平了道路。
