Testing the fate of nascent holes in CdSe nanocrystals with sub-10 fs pump–probe spectroscopy

Abstract

The absence of hole state filling effects on CdSe nanocrystal TA is shown not to reflect ultrafast hole trapping using sub 10 fs pump–probe spectroscopy.

Unusually Strong Biexciton Repulsion Detected in Quantum Confined CsPbBr3 Nanocrystals with Two and Three Pulse Femtosecond Spectroscopy

“…The observed behavior is very similar to the case of CdSe NCs where, for reasons which remain debated, BE hole state occupation does not bleach the 1S e 1S h exciton band. 45,46 In MLHP, it is not clear in which band state filling effects are lacking, and this result is inconsistent with a scavenging study by Lian and co-workers which shows that in similarly sized NCs, extraction of electrons or holes by molecular scavengers leads to elimination of 70% and 30% of the BE bleach in TA experiments, respectively. 47 Further study will be required to determine why the expected equivalent effect of valence and conduction state filling is not realized and to understand why the effective integral biexciton bleach is only equal to the initial 1S e 1S h absorption.…”

“…Further study will be required to determine why the expected equivalent effect of valence and conduction state filling is not realized and to understand why the effective integral biexciton bleach is only equal to the initial 1S e 1S h absorption. It is noteworthy that, as in ref , even with the high time resolution 2 and 3 pulse pump–probe employed here, no initial signs of net emission were observed for biexciton, ruling out carrier trapping as a likely explanation for its curious absence.…”

Unusually Strong Bi-Exciton Repulsion Detected in Quantum Confined CsPbBr3 Nanocrystals with Two and Three Pulse Femtosecond Spectroscopy

“…The observed behavior is very similar to the case of CdSe NCs where for reasons which remain debated, BE hole state occupation does not bleach the 1Se1Sh exciton band. 45,46 In MLHP it is not clear in which band state filling effects are lacking, and this result is inconsistent with a scavenging study by Lian and coworkers which shows that in similarly sized NCs extraction of electrons or holes by molecular scavengers leads to elimination of 70 % and 30% of the BE bleach in TA experiments respectively. 47 Further study will be required to determine why the expected equivalent effect of valence and conduction state filling is not realized, and to understand why the effective integral bi-exciton bleach is only equal to the initial 1Se1Sh absorption.…”

Solving Quantum-Dot Excitonic Riddles with Absolute Pump–Probe Spectroscopy

“…The complexity of lead chalcogenide QD electronic structure makes quantitative analysis of these results challenging . In contrast, in the case of CdSe QDs, lower BE state degeneracy and state filling effects only due to conduction band carriers ,,, promise more straightforward interpretation. Figure presents results for a sample of CdSe QDs capped with a thin CdS layer to reduce carrier trapping observed in ligand-passivated core samples .…”

“…The rationale was that the process of photoexcitation in the lowest exciton state would necessarily populate not only electron states but also hole levels involved in this bright transition. Aside from using very short pulses, the method was straightforward low-intensity PP where both pump and probe were derived from the ∼7 fs output of a nonlinear optical parametric amplifier (NOPA) . Any short-lived population of bright hole states would give rise to an initial bleach per exciton exceeding half of the BE cross section (double state degeneracy of the 1Se state).…”