Lead halide perovskite quantum dots (QDs) are a promising material for light amplification devices. In order to improve their optical gain threshold and lifetime, it is essential to understand the underlying gain mechanism. However, there is still debate on the nature of gain in perovskite QDs, which has been attributed to different origins such as biexcitons, trions, and single excitons. Here we study amplified spontaneous emission and optical gain of monodisperse spherical CsPbBr₃ QDs and conclusively assign the gain to biexcitons. This is based on the gain threshold and its spectral position which we study via femtosecond transient absorption spectroscopy. Furthermore, the optical gain vanishes within 30 ps, matching the biexciton lifetime, demonstrating the strong correlation to the biexciton population. By identifying the intrinsic mechanism of optical gain in CsPbBr₃ QDs and its limiting factors, our findings show the direction for future work on optimizing their gain threshold and lifetime.

中文翻译：

---

CsPbBr3 量子点中的双激子光增益


铅卤化物钙钛矿量子点 （QD） 是一种很有前途的光放大器件材料。为了提高其光增益阈值和寿命，必须了解潜在的增益机制。然而，关于钙钛矿 QD 增益的性质仍然存在争议，这归因于不同的来源，例如双激子、trion 和单激子。在这里，我们研究了单分散球形 CsPbBr₃ QD 的放大自发发射和光增益，并最终将增益分配给双激子。这是基于增益阈值及其光谱位置，我们通过飞秒瞬态吸收光谱对其进行研究。此外，光增益在 30 ps 内消失，与双激子寿命相匹配，表明与双激子群具有很强的相关性。通过确定 CsPbBr₃ QD 中光增益的内在机制及其限制因素，我们的研究结果为未来优化其增益阈值和寿命的工作指明了方向。