Perovskite quantum dots (QDs) are promising nanostructures for optoelectronics, especially for the application to light emitting devices or single photon sources. CsPbX3 inorganic QDs or FAPbX3 hybrid QDs (X=I, Br, Cl and FA= formamidinium) are especially attractive. The authors of the present work have directly adressed in a previous paper on FAPbBr3 QDs (Tamarat et al, Nature materials 2019), the controversy on the nature of the exciton ground state, demonstrating that it corresponds to a singlet dark exciton state. The exceptional brillancies and high quantum yields of these nano-objects are attributed to the absence of one-phonon assisted classical relaxations from the exciton bright triplet to the exciton dark state, first revealed on FAPbI3 QDs in Fu et al Nature Comm. 2018. The present work confirms these results on inorganic CsPbI3 QDs and further evidences the cascade emission of correlated photon-pairs from the biexciton state. Photon bunching remains visible up to about 40 K in CsPbI3 QDs, while it vanishes at about 10 K in classical CdSe QDs. This effect is again attributed to the lack of efficiency of the dark exciton singlet as a diversion channel.
 Jacky EVEN
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+33 2 23 23 82 95LP2N (CNRS-Université de Bordeaux, France), EMPA (Dübendorf, Switzerland), ETH Zurich (Switzerland)
The dark exciton ground state promotes photon-pair emission in individual perovskite nanocrystals, P. Tamarat , L. Hou , J.-B. Trebbia , A. Swarnkar , L. Biadala , Y. Louyer , M.I. Bodnarchuk , M.V. Kovalenko , J. Even & B. Lounis Nat. Commun. Vol. 11, 6001, 2020, DOI : 10.1038/s41467-020-19740-7
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