Diroll Benjamin T, Banerjee Tathagata
Center for Nanoscale Materials, Argonne National Laboratory, USA.
Department of Physics, University of Illinois Urbana-Champaign, USA.
Nanoscale. 2022 Jan 27;14(4):1340-1346. doi: 10.1039/d1nr06203d.
Hot electrons, far above the lattice temperature of a material, present opportunities for enhanced solar energy harvesting or performance of otherwise unfavorable chemistry. The spectroscopic signatures and dynamics of hot carrier absorption and emission have been extensively studied in bulk and nanoscopic semiconductors, but the effects on intraband transitions are largely unexplored. Here, the effect of hot electrons on the properties of colloidal quantum wells made of cadmium selenide is examined using ultrafast spectroscopy. Similar to expitaxial quantum wells, these atomically precise materials support intersubband transitions (a class of intraband transitions in 1D and 2D materials) in the near-infrared spectral window. Using energy-dependent photoexcitation, it is shown that electrons reach effective temperatures of 2000 K or greater. This results in a substantial transient shift in the oscillator strength of the instersubband transition to lower energies on a sub-picosecond time-scale. Similar heating of electrons is achieved under mid-infrared re-excitation, which permits ultrafast transmittance modulation throughout the near-infrared.
热电子的温度远高于材料的晶格温度，为增强太阳能收集或实现原本不利的化学反应提供了机会。热载流子吸收和发射的光谱特征及动力学已在体相和纳米半导体中得到广泛研究，但对带内跃迁的影响在很大程度上尚未被探索。在此，利用超快光谱研究了热电子对由硒化镉制成的胶体量子阱性质的影响。与外延量子阱类似，这些原子精确的材料在近红外光谱窗口支持子带间跃迁（一维和二维材料中的一类带内跃迁）。通过能量相关的光激发表明，电子能达到2000 K或更高的有效温度。这导致子带间跃迁的振子强度在亚皮秒时间尺度上大幅瞬态向更低能量偏移。在中红外再激发下也能实现类似的电子加热，从而允许在整个近红外范围内进行超快透射率调制。
