Publication date: 3rd July 2020
Lead halide perovskites have emerged as promising new semiconductor materials for high-efficiency photovoltaics, light-emitting applications and quantum optical technologies. Their luminescence properties are governed by the formation and radiative recombination of bound electron-hole pairs known as excitons, whose bright or dark character of the ground state remains debated [1, 2].
Spectroscopically resolved emission from single lead halide perovskite nanocrystals at cryogenic temperatures provides unique insight into physical processes that occur within these materials. At low temperatures the emission spectra collapse to narrow lines revealing a rich spectroscopic landscape and unexpected properties, completely hidden at the ensemble level and in bulk materials.
In this talk, I will discuss how magneto-photoluminescence spectroscopy provides a direct spectroscopic signature of the dark exciton emission of single lead halide perovskite nanocrystals [3]. The dark singlet is located several millielectronvolts below the bright triplet, in fair agreement with an estimation of the long-range electron-hole exchange interaction. Nevertheless, these perovskites display an intense luminescence because of an extremely reduced bright-to-dark phonon-assisted relaxation [4]. Resonant photoluminescence excitation spectroscopy allows the determination of the optical coherence lifetimes in these nanocrystals and to assess their suitability as sources of indistinguishable single photons [5]. Memories in the Photoluminescence Intermittency of Single Cesium Lead Bromide Nanocrystals are observed [6].
References:
[1] M. Fu, P. Tamarat, J. Even, A. L. Rogach, and B. Lounis, “Neutral and Charged Exciton Fine Structure in Single Lead Halide Perovskite Nanocrystals Revealed by Magneto-optical Spectroscopy” Nano Lett., 17, (2017) 2895–2901.
[2] G. Nedelcu, A. Shabaev, T. Stöferle, R. F. Mahrt, M. V. Kovalenko, D. J. Norris, G. Rainò, and A. L. Efros, “Bright triplet excitons in cesium lead halide perovskites” Nature 553 (2018) 189–193.
[3] P. Tamarat, M. I. Bodnarchuk, J.-B. Trebbia, R. Erni, M. V. Kovalenko, J. Even, and B. Lounis, “The ground exciton state of formamidinium lead bromide perovskite nanocrystals is a singlet dark state,” Nat. Mater., 18 (2019) 717-724.
[4] M. Fu, P. Tamarat, J.-B. Trebbia, M. I. Bodnarchuk, M. V. Kovalenko, J. Even, and B. Lounis, “Unraveling exciton-phonon coupling in individual FAPbI3 nanocrystals emitting near-infrared single photons" Nat. Commun. 9 (2018) 3318.
[5] P. Tamarat et al., submitted (2020)
[6] L. Hou, C. Zhao, X. Yuan, J. Zhao, F. Krieg, P. Tamarat, M. V. Kovalenko, C. Guo, B. Lounis, "Memories in the Photoluminescence Intermittency of Single Cesium Lead Bromide Nanocrystals" Nanoscale 12 (2020) 6795-6802
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