Reducing the Optical Gain Threshold in Two-Dimensional CdSe Nanoplatelets by the Giant Oscillator Strength Transition Effect
Reducing the Optical Gain Threshold in Two-Dimensional CdSe Nanoplatelets by the Giant Oscillator Strength Transition Effect
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DOI：
10.1021/acs.jpclett.9b00759
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发表时间：
2019-04-04
影响因子：
5.7
通讯作者：
Lian, Tianquan
中科院分区：
文献类型：
--
作者：
Li, Qiuyang;Liu, Qiliang;Lian, Tianquan
二维CdSe纳米片是一种很有前途的激光材料。它们的大横向面积通过增加振子强度和多激子寿命来降低光学增益阈值，但也通过需要多个带边激子（>2）来达到光学增益来增加增益阈值。我们观察到，在4 K的CdSe纳米片的光增益阈值是类似的4倍，低于在室温下。瞬态吸收光谱测量表明，室温下激子质心相干区小于横向尺寸，在4 K时几乎扩展到整个纳米片。这表明，在低温下的光学增益阈值的减少可以归因于激子相干区域扩展，其减少了带边激子的饱和数以实现双激子增益并增加了辐射衰减速率，这与巨振子强度跃迁效应一致。这项工作为降低纳米材料的光学增益阈值提供了一个新的方向。
Two-dimensional CdSe nanoplatelets are promising lasing materials. Their large lateral areas reduce the optical gain threshold by increasing the oscillator strength and multiexciton lifetimes but also increase the gain threshold by requiring multiple band-edge excitons (>2) to reach the optical gain. We observe that the optical gain threshold of CdSe nanoplatelets at 4 K is similar to 4-fold lower than that at room temperature. Transient absorption spectroscopy measurements indicate that the exciton center-of-mass coherent area is smaller than the lateral size at room temperature and extends to nearly the whole nanoplatelets at 4 K. This suggests that the reduction in the optical gain threshold at a low temperature can be attributed to exciton coherent area extension that reduces the saturation number of band-edge excitons to enable biexciton gain and increases the radiative decay rate, consistent with the giant oscillator strength transition effect. This work demonstrates a new direction for lowering the optical gain threshold of nanomaterials.