Stimulated Emission through an Electron-Hole Plasma in Colloidal CdSe Quantum Rings

Carmelita Rodà^a^,^b^,^c, Bastiaan B.V. Salzmann^d, Isabella Wagner^e^,^f, Yera Ussembayev^b^,^g, Kai Chen^f^,^h^,ⁱ, Justin Hodgkiss^e^,^f, Iwan Moreels^a^,^b^,^c, Kristiaan Neyts^b^,^g, Daniel Vanmaekelbergh^d, Pieter Geiregat^a^,^b^,^c

^aPhysics and Chemistry of Nanostructures, Department of Chemistry, Ghent University, Belgium, Krijgslaan 281 - S3, Ghent, Belgium

^bPhotonics Research Group, Ghent University, Belgium, Technologiepark-Zwijnaarde, 126, Gent, Belgium

^cCenter for Nano and Biophotonics, Ghent University, Belgium, Belgium

^dDebye Institute for Nanomaterials Science, Utrecht University, Heidelberglaan, 8, Utrecht, Netherlands

^eSchool of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand, PO Box 600, Wellington, New Zealand

^fMacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand., PO Box 600, Wellington, New Zealand

^gLiquid Crystals and Photonics Research Group, Department of Information Technology, Ghent University, Ghent, Belgium

^hRobinson Research Institute, Victoria University of Wellington, Wellington, New Zealand, PO Box 600, Wellington, New Zealand

ⁱThe Dodd-Walls Centre for Photonic and Quantum Technologies, University of Otago, PO Box 56, Dunedin, New Zealand

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2021 (NFM21)

#NCFun21. Fundamental Processes in Nanocrystals and 2D Materials

Online, Spain, 2021 October 18th - 22nd

Organizers: Brandi Cossairt and Jonathan De Roo

Contributed talk, Carmelita Rodà, presentation 152
DOI: https://doi.org/10.29363/nanoge.nfm.2021.152
Publication date: 23rd September 2021

Colloidal CdSe quantum rings (QRs) are a new class of nanomaterials synthetized via thermo-chemical edge reconfiguration of thinner CdSe nanoplatelets [1],[2]. In the latter, the photo-physics is consistently dominated by strongly bound electron-hole pairs, so-called excitons, that can merge to form excitonic molecules (biexcitons), giving rise to net stimulated emission along the molecule-to-exciton recombination pathway.[3] On the other hand, little is known on the nature of elementary excitations in thicker CdSe QRs - whether they are excitons or free electron-hole pairs- and their behavior at high density regime. Here, we show that charge carriers in QRs condense into a hot uncorrelated electron-plasma at high density opposed to the stable exciton gas found in thinner nanoplatelets. Through strong band gap renormalization, this plasma state is able to produce sizable optical gain with a broadband spectrum. Next, we show that the typical signatures of excitonic transitions are indeed absent in QRs. The gain is limited by a second order radiative recombination process and the buildup is counteracted by a typical charge cooling bottleneck. Overall, our results show that weakly confined QRs are a unique system to study uncorrelated electron-hole dynamics in nanoscale materials.

References:

[1] Fedin, I.; Talapin, D. V. Colloidal CdSe Quantum Rings. J. Am. Chem. Soc. 2016, 138, 9771-9774.

[2] Salzman, B.; Vliem, J.; Maaskant, N.; Post, C.; Li, C.; Bals, S.; Vanmaekelbergh, D. From CdSe nanoplatelets to quantum rings by thermochemical edge reconguration. Chem. Mater. 2021.

[3] Geiregat, P.; Tomar, R.; Chen, K.; Singh, S.; Hodgkiss, J. M.; Hens, Z. Thermodynamic Equilibrium between Excitons and Excitonic Molecules Dictates Optical Gain in Colloidal CdSe Quantum Wells. J. Phys. Chem. Lett 2019, 10, 3637-3644.

Acknowledgements:

P. G. acknowledges support from FWO-Vlaanderen (12K8216N). This project has received
funding from the European Research Council (ERC) under the European Union's Horizon
2020 research and innovation program (grant agreement no. 714876 PHOCONA). B.B.V.S.
and D.V. acknowledge the Dutch NWO for financial support via the TOP-ECHO grant nr.
715.016.002. D.V. acknowledges financial support from the European ERC Council, ERC
Advanced grant 692691 "First Step".

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