Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.203
Publication date: 16th December 2024
Quantum dots (QDs) offer unique physical properties and novel application possibilities like single-photon emitters for quantum technologies. While strongly-confined II-VI and III-V QDs have been studied extensively, their complex valence band structure often limits clear observations of individual transitions. In recently emerged lead-halide perovskites, band-degeneracies are absent around the bandgap reducing the complexity of optical spectra. These QDs exhibit several distinct absorption resonances,[1] which can be assigned to excitons confined with respect to their center-of-mass motion within the weak confinement regime. [2] The well-defined excitonic energy landscape with significant confinement energies of these QDs suggests a high potential for light amplification. However, there is still debate on the nature of gain in perovskite QDs, which has been attributed to different origins such as biexcitons, trions, and single excitons. Here we study amplified spontaneous emission and optical gain of monodisperse spherical CsPbBr3 QDs and conclusively assign the gain to biexcitons.[3] This is based on the gain threshold and its spectral position which we study via femtosecond transient absorption spectroscopy. Furthermore, the optical gain vanishes within 30 ps, matching the biexciton lifetime, demonstrating the strong correlation to the biexciton population. By identifying the intrinsic mechanism of optical gain in CsPbBr3 QDs and its limiting factors, our findings show the direction for future work on optimizing their gain threshold and lifetime.
This work was supported by the Bavarian State Ministry of Science and Arts and by the LMU Munich through the grant “Solar Technologies go Hybrid” (SolTech). Q.A.A. acknowledges the LMUexcellent, funded by the Federal Ministry of Education and Research (BMBF) and the Free State of Bavaria under the Excellence Strategy of the Federal Government and the Länder. We thank local research clusters and centers such as the Center for NanoScience (CeNS) for providing communicative networking structures.
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