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（QD）作为可溶液处理和可调光增益材料引起了越来越多的关注。但是，特别是对于红外有源QD，光学增益仍然很低。由于受激发射涉及多个简并的带边缘状态，因此只能在高泵浦功率下才能实现种群反转，并且必须与有效的多激子复合竞争。在这里，我们显示出碲化汞（HgTe）量子点在整个近红外电信窗口中显示出大小可调的受激发射，其阈值是之前研究的任何量子点所无法比拟的。我们将此独特行为归因于带隙中的表面局部状态，这些状态将HgTe QD转变为4级系统。在连续波光泵浦下，在与太阳辐射和直流电泵浦兼容的功率水平下，由此产生的寿命长的种群倒置会引发放大的自发发射。这些结果介绍了一种基于故意陷波状态的基于低阈值QD的增益介质的替代方法，为溶液处理的红外QD激光器和放大器铺平了道路。