Gain roll-off in cadmium selenide colloidal quantum wells under intense optical excitation

Journal Article · 15 May 2022 · Scientific Reports

DOI: https://doi.org/10.1038/s41598-022-11882-6 · OSTI ID:1960731

Diroll, Benjamin T. ^[1]; Brumberg, Alexandra ^[2]; Schaller, Richard D. ^[3]

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1. Argonne National Lab. (ANL), Lemont, IL (United States). Center for Nanoscale Materials
2. Northwestern Univ., Evanston, IL (United States)
3. Argonne National Lab. (ANL), Lemont, IL (United States). Center for Nanoscale Materials; Northwestern Univ., Evanston, IL (United States)

Colloidal quantum wells, or nanoplatelets, show among the lowest thresholds for amplified spontaneous emission and lasing among solution-cast materials and among the highest modal gains of any known materials. Using solution measurements of colloidal quantum wells, this work shows that under photoexcitation, optical gain increases with pump fluence before rolling off due to broad photoinduced absorption at energies lower than the band gap. Despite the common occurrence of gain induced by an electron–hole plasma found in bulk materials and epitaxial quantum wells, under no measurement conditions was the excitonic absorption of the colloidal quantum wells extinguished and gain arising from a plasma observed. Instead, like gain, excitonic absorption reaches a minimum intensity near a photoinduced carrier sheet density of 2 × 10¹³ cm^–2 above which the absorption peak begins to recover. To understand the origins of these saturation and reversal effects, measurements were performed with different excitation energies, which deposit differing amounts of excess energy above the band gap. Across many samples, it was consistently observed that less energetic excitation results in stronger excitonic bleaching and gain for a given carrier density. Transient and static optical measurements at elevated temperatures, as well as transient X-ray diffraction of the samples, suggest that the origin of gain saturation and reversal is a heating and disordering of the colloidal quantum wells which produces sub-gap photoinduced absorption.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: 3M; National Science Foundation (NSF); Northwestern University; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1960731
• Journal Information: Scientific Reports, Journal Name: Scientific Reports Journal Issue: 1 Vol. 12; ISSN 2045-2322
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United States
• Language: English