Dana Jayanta, Binyamin Tal, Etgar Lioz, Ruhman Sanford
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem-91904, Israel.
ACS Nano. 2021 May 25;15(5):9039-9047. doi: 10.1021/acsnano.1c02123. Epub 2021 May 11.
Transient absorption measurements were conducted on pristine and monoexciton saturated CsPbBr nanocrystals varying in size within the regime of a strong quantum confinement. Once the difference spectra were translated to absolute transient changes in absorption cross section, a single exciton is shown to completely bleach the band edge absorption peak and induce a new absorption roughly two times weaker ∼100 meV to the blue. Difference spectra obtained during Auger recombination of biexciton demonstrate that the addition of a second exciton, rather than double the effect of a first, bleaches the blue-induced absorption band without producing a net stimulated emission at the band edge. Accompanied by high time resolution transient absorption spectra pumping at the lowest exciton band, these results identify the blue-induced absorption as the second transition to 1S1S which is shifted in energy due to unusually strong and promptly rising biexciton repulsion. Possible mechanisms giving rise to this repulsion and prospects for applying it to enhance optical gain applications of these particles are discussed.
在强量子限制区域内，对尺寸不同的原始和单激子饱和CsPbBr纳米晶体进行了瞬态吸收测量。一旦将差分光谱转换为吸收截面的绝对瞬态变化，就会发现单激子会完全漂白带边吸收峰，并在蓝移约100 meV处诱导出一个强度约为其两倍的新吸收峰。在双激子俄歇复合过程中获得的差分光谱表明，添加第二个激子，而不是使第一个激子的效应加倍，会漂白蓝移诱导的吸收带，而不会在带边产生净受激发射。伴随着在最低激子带泵浦的高时间分辨率瞬态吸收光谱，这些结果确定蓝移诱导的吸收是到1S1S的第二个跃迁，由于异常强烈且迅速上升的双激子排斥作用，其能量发生了偏移。讨论了产生这种排斥作用的可能机制以及将其应用于增强这些粒子的光学增益应用的前景。
