With the progress in the synthesis of CsPbX3 quantum dots (QDs) in strongly confined regime with high ensemble uniformity, quantum-confined exciton transitions at various levels can now be clearly resolved. Taking advantage of the clearer exciton absorption peaks in the linear optical spectra in these QDs, we revealed the unusual effect of bandedge exciton on the forbidden exciton transitions in CsPbBr3 QDs. Pump-probe transient absorption spectra of the QDs show a narrow and intense pump-induced absorption between the first two allowed exciton transition peaks, which is distrinctly different from the behavior of unconfined counterpart. The pump-induced absorption exhibits the identical dynamics as the bandedge exciton relaxation, while it cannot be explained by the usual excited state absorption. This feature is attributed to the formally dipole-forbidden exciton transition that turns on in the presence of the bandedge exciton that may have modified the selection rule by breaking the symmetry. The confined space of the QDs and possible formation of the localized bandedge exciton with large dipole may be responsible for this unique biexcitonic phenomenon in CsPbBr3 QDs enabling the access to the previously inaccessible state.

Turning on forbidden exciton transition in strongly confined CsPbBr3 quantum dots by photoexcitation of bandedge exciton

256th National Meeting (2018)

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