Engineering Perovskite Nanocrystals as Versatile Quantum Emitters

Lead halide perovskite nanocrystals (LHP NCs) are of broad interest as classical light sources (LED/LCD displays) and as quantum light sources. The current development in LHP NC surface chemistry, using designer phospholipid capping ligands, allows for their increased stability down to single particle level [1]. The brightness of such a quantum emitter is ultimately described by Fermi’s golden rule, where a radiative rate is proportional to its oscillator strength (intrinsic emitter property) and the local density of photonic states (photonic engineering, i.e., cavity). With perovskite NCs, we demonstrated a record-low sub-100 ps radiative decay time for CsPb(Br/Cl)₃, almost as short as the reported exciton coherence time, by the NC size increase to 30 nm [2]. The formation of giant transition dipoles was reasoned based on effective mass calculations for the case of the giant oscillator strength. Importantly, the fast radiative rate is achieved along with the single-photon emission despite the NC size being ten times larger than the exciton Bohr radius. At room temperature and shifting to hybrid organic-inorganic LHP NCs, we could make use of strongly enhanced structure dynamics to break the size dependence of the single-photon purity observed in conventional semiconductor NCs. In particular, phonon-induced localization of the exciton wavefunction is corroborated by the ab initio molecular dynamics AIMD. Avoiding the trade-off between single-photon purity and optical stability faced by downsizing nanocrystals into the strong confinement regime, we observe bright (10⁶ photons/s), stable (>1h), and pure (>95%) single-photon emission in a widely tuneable spectral range (495-745 nm) in formamidine-based LHP NCs [3].

[1] V. Morad, A. Stelmakh, M. Svyrydenko, L.G. Feld, S.C. Boehme, M. Aebli, J. Affolter, C.J. Kaul, N.J. Schrenker, S. Bals, Y. Sahin, D.N. Dirin, I. Cherniukh, G. Raino, A. Baumketner, M.V. Kovalenko Nature, 2024, 626, 542–548
[2] C. Zhu, S.C. Boehme, L.G. Feld, A. Moskalenko, D.N. Dirin, R.F. Mahrt, T. Stöferle, M.I. Bodnarchuk, A.L. Efros, P.C. Sercel, M.V. Kovalenko, G. Rainò. Nature, 2024, 626, 535–541
[3] L.G. Feld, S.C. Boehme, S. Sabisch, N. Frenkel, N. Yazdani, V. Morad, C. Zhu, M. Svyrydenko, R. Tao, M. Bodnarchuk, G. Lubin, M. Kazes, V. Wood, D. Oron, G. Rainò, M.V. Kovalenko. arrXiv:2404.15920 (24 April 2024)