Center for Nanoscale Materials, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, IL 60439, United States of America.
Nanotechnology. 2023 Mar 29;34(24). doi: 10.1088/1361-6528/acc40c.
The optical Stark effect is a universal response of the electronic structure to incident light. In semiconductors, particularly nanomaterials, the optical Stark effect achieved with sub-band gap photons can drive large, narrowband, and potentially ultrafast changes in the absorption or reflection at the band gap through excitation of virtual excitons. Rapid optical modulation using the optical Stark effect is ultimately constrained, however, by the generation of long-lived excitons through multiphoton absorption. This work compares the modulation achievable using the optical Stark effect on CdSe nanoplatelets with several different pump photon energies, from the visible to mid-infrared. Despite expected lower efficiencies for spectrally-remote pump energies, infrared pump pulses can ultimately drive larger sub-picosecond optical Stark shifts of virtual excitons without creation of real excitons. The CdSe nanoplatelets show subpicosecond shifts of the lowest excitonic resonance of up to 22 meV, resulting in change in absorption as large as 0.32 OD (49% increase in transmission), with a long-lived offset from real excitons less than 1% of the peak signal.
光斯塔克效应是电子结构对入射光的普遍响应。在半导体中，特别是纳米材料中，用光的斯塔克效应实现亚带隙光子可以通过激发虚拟激子，在带隙处实现大的、窄带和潜在超快的吸收或反射变化。然而，光斯塔克效应的快速光调制最终受到通过多光子吸收产生长寿命激子的限制。这项工作比较了 CdSe 纳米板在不同泵浦光子能量（从可见光到中红外）下，利用光斯塔克效应实现的调制。尽管对于光谱上较远的泵浦能量的效率预期较低，但红外泵浦脉冲最终可以驱动更大的亚皮秒虚拟激子的光斯塔克位移，而不会产生真实激子。CdSe 纳米板显示出低激子共振的亚皮秒位移，最大可达 22 毫电子伏特，导致吸收的变化高达 0.32 OD（传输增加 49%），与真实激子的长寿命偏移小于峰值信号的 1%。
