Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.074
Publication date: 7th February 2022
Semiconducting lead halide perovskites are excellent candidates for realizing low threshold light amplification due to their tunable and highly efficient luminescence, ease of processing and strong light-matter interactions. Indeed, several solution processable lasers have been demonstrated, even operating under nanosecond and continuous wave optical pumping. All of these examples use perovskite architectures with little to no confinement, for example using bulk films, nanowires or quantum dots (QDs) with average sizes well above the Bohr diameter. As such, there is no clear picture whether the use of perovskites in the strong 3D confinement regime would be beneficial, nor is there any insight in how optical gain would develop under those conditions. Here, we show through a combination of quantitative transient absorption and femtosecond fluorescence spectroscopy, that optical gain in strongly confined perovskite 0-dimensional QDs develops at remarkably low average exciton numbers per nanocrystal (<N> << 1). The gain magnitude is however smaller compared to bulk-like perovskite systems and the lifetime is capped by rapid Auger recombination. We are able to explain our observations using a 3-level model that takes both the strong exciton-exciton repulsion and Stokes shift due to electron-phonon coupling into account of strongly confined QDs. The enhanced repulsions and shifts act as a double edge sword, reducing the gain threshold but decreasing gain magnitude and lifetime. The concepts shown here provide a rational approach to look for low threshold optical gain materials based on an optimal interplay between electronic and vibrational degrees of freedom.
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